# Percentage difference between images

Percentage difference between images
You are encouraged to solve this task according to the task description, using any language you may know.
Compute the percentage of difference between 2 JPEG images of the same size. Alternatively, compare two bitmaps as defined in basic bitmap storage.

Useful for comparing two JPEG images saved with a different compression ratios.

You can use these pictures for testing (use the full-size version of each):

50% quality JPEG 100% quality JPEG
link to full size 50% image link to full size 100% image

The expected difference for these two images is 1.62125%

`type Count is mod 2**64;`

1-norm distance in the luminance space:

`function "-" (Left, Right : Luminance) return Count isbegin   if Left > Right then      return Count (Left) - Count (Right);   else      return Count (Right) - Count (Left);   end if;end "-";`

1-norm distance in the color space multiplied to 3:

`function "-" (Left, Right : Pixel) return Count isbegin   return (Left.R - Right.R) + (Left.G - Left.G) + (Left.B - Right.B);end "-";`

Mean of 1-norm distances. Constraint_Error is propagated when images have different size.

`function Diff (Left, Right : Image) return Float is   Offs_I : constant Integer := Right'First (1) - Left'First (1);   Offs_J : constant Integer := Right'First (2) - Left'First (2);   Sum : Count := 0;begin   if Left'Length (1) /= Right'Length (1) or else Left'Length (2) /= Right'Length (2) then      raise Constraint_Error;   end if;   for I in Left'Range (1) loop      for J in Left'Range (2) loop         Sum := Sum + (Left (I, J) - Right (I + Offs_I, J + Offs_J));      end loop;   end loop;   return Float (Sum) / (3.0 * Float (Left'Length (1) * Left'Length (2)));end Diff;`

Example of use:

`   F1, F2 : File_Type;begin   Open (F1, In_File, "city.ppm");   Open (F2, In_File, "city_emboss.ppm");   Ada.Text_IO.Put_Line ("Diff" & Float'Image (Diff (Get_PPM (F1), Get_PPM (F2))));   Close (F1);   Close (F2);`

## AutoHotkey

Works with: AutoHotkey_L

uses gdip.ahk

`startup()dibSection := getPixels("lenna100.jpg")dibSection2 := getPixels("lenna50.jpg") ; ("File-Lenna100.jpg")pixels := dibSection.pBitspixels2 := dibSection2.pBitsz := 0loop % dibSection.width * dibSection.height * 4{x := numget(pixels - 1, A_Index, "uchar") y := numget(pixels2 - 1, A_Index, "uchar")z += abs(y - x)}msgbox % z / (dibSection.width * dibSection.height * 3 * 255 / 100 ) ; 1.626return CreateDIBSection2(hDC, nW, nH, bpp = 32, ByRef pBits = ""){dib := object()	NumPut(VarSetCapacity(bi, 40, 0), bi)	NumPut(nW, bi, 4)	NumPut(nH, bi, 8)	NumPut(bpp, NumPut(1, bi, 12, "UShort"), 0, "Ushort")	NumPut(0,  bi,16)hbm := DllCall("gdi32\CreateDIBSection", "Uint", hDC, "Uint", &bi, "Uint", 0, "UintP", pBits, "Uint", 0, "Uint", 0) dib.hbm := hbmdib.pBits := pBitsdib.width := nWdib.height := nHdib.bpp := bppdib.header := header	Return	dib}   startup(){global disposablesdisposables := object()disposables.pBitmaps := object()disposables.hBitmaps := object() If !(disposables.pToken := Gdip_Startup()){	MsgBox, 48, gdiplus error!, Gdiplus failed to start. Please ensure you have gdiplus on your system	ExitApp}  OnExit, gdipExit}  gdipExit:loop % disposables.hBitmaps._maxindex()DllCall("DeleteObject", "Uint", disposables.hBitmaps[A_Index])Gdip_Shutdown(disposables.pToken)ExitApp getPixels(imageFile){global disposables ; hBitmap will be disposed laterpBitmapFile1 := Gdip_CreateBitmapFromFile(imageFile)hbmi := Gdip_CreateHBITMAPFromBitmap(pBitmapFile1)width := Gdip_GetImageWidth(pBitmapFile1)height := Gdip_GetImageHeight(pBitmapFile1) 	mDCo := DllCall("CreateCompatibleDC", "Uint", 0)	mDCi := DllCall("CreateCompatibleDC", "Uint", 0)	dibSection := CreateDIBSection2(mDCo, width, height)	hBMo := dibSection.hbm 	oBM := DllCall("SelectObject", "Uint", mDCo, "Uint", hBMo)	iBM := DllCall("SelectObject", "Uint", mDCi, "Uint", hbmi) 	DllCall("BitBlt", "Uint", mDCo, "int", 0, "int", 0, "int", width, "int", height, "Uint", mDCi, "int", 0, "int", 0, "Uint", 0x40000000 | 0x00CC0020) 	DllCall("SelectObject", "Uint", mDCo, "Uint", oBM)DllCall("DeleteDC", "Uint", 0, "Uint", mDCi)DllCall("DeleteDC", "Uint", 0, "Uint", mDCo)Gdip_DisposeImage(pBitmapFile1)DllCall("DeleteObject", "Uint", hBMi)disposables.hBitmaps._insert(hBMo)return dibSection}#Include Gdip.ahk  ; Thanks to tic (Tariq Porter) for his GDI+ Library `

## BBC BASIC

I would have preferred to calculate the RMS difference but it would be inconsistent with other results.

`      hbm1% = FNloadimage("C:lenna50.jpg")      hbm2% = FNloadimage("C:lenna100.jpg")       SYS "CreateCompatibleDC", @memhdc% TO hdc1%      SYS "CreateCompatibleDC", @memhdc% TO hdc2%       SYS "SelectObject", hdc1%, hbm1%      SYS "SelectObject", hdc2%, hbm2%       diff% = 0      FOR y% = 0 TO 511        FOR x% = 0 TO 511          SYS "GetPixel", hdc1%, x%, y% TO rgb1%          SYS "GetPixel", hdc2%, x%, y% TO rgb2%          diff% += ABS((rgb1% AND &FF) - (rgb2% AND &FF))          diff% += ABS((rgb1% >> 8 AND &FF) - (rgb2% >> 8 AND &FF))          diff% += ABS((rgb1% >> 16) - (rgb2% >> 16))        NEXT      NEXT y%      PRINT "Image difference = "; 100 * diff% / 512^2 / 3 / 255 " %"       SYS "DeleteDC", hdc1%      SYS "DeleteDC", hdc2%      SYS "DeleteObject", hbm1%      SYS "DeleteObject", hbm2%      END       DEF FNloadimage(file\$)      LOCAL iid{}, hbm%, pic%, ole%, olpp%, text%      DIM iid{a%,b%,c%,d%}, text% LOCAL 513       iid.a% = &7BF80980 : REM. 128-bit iid      iid.b% = &101ABF32      iid.c% = &AA00BB8B      iid.d% = &AB0C3000       SYS "MultiByteToWideChar", 0, 0, file\$, -1, text%, 256       SYS "LoadLibrary", "OLEAUT32.DLL" TO ole%      SYS "GetProcAddress", ole%, "OleLoadPicturePath" TO olpp%      IF olpp%=0 THEN = 0       SYS olpp%, text%, 0, 0, 0, iid{}, ^pic% : REM. OleLoadPicturePath      IF pic%=0 THEN = 0       SYS !(!pic%+12), pic%, ^hbm% : REM. IPicture::get_Handle      SYS "FreeLibrary", ole%      = hbm%`

Output:

```Image difference = 1.6255931 %
```

## C

The read_image function is from here.

`#include <stdio.h>#include <stdlib.h>#include <math.h>/* #include "imglib.h" */ #define RED_C 0#define GREEN_C 1#define BLUE_C 2#define GET_PIXEL(IMG, X, Y) ((IMG)->buf[ (Y) * (IMG)->width + (X) ]) int main(int argc, char **argv){   image im1, im2;   double totalDiff = 0.0;   unsigned int x, y;    if ( argc < 3 )   {      fprintf(stderr, "usage:\n%s FILE1 FILE2\n", argv[0]);      exit(1);   }   im1 = read_image(argv[1]);   if ( im1 == NULL ) exit(1);   im2 = read_image(argv[2]);   if ( im2 == NULL ) { free_img(im1); exit(1); }   if ( (im1->width != im2->width) || (im1->height != im2->height) )   {      fprintf(stderr, "width/height of the images must match!\n");   } else {   /* BODY: the "real" part! */      for(x=0; x < im1->width; x++)      {         for(y=0; y < im1->width; y++)         {           totalDiff += fabs( GET_PIXEL(im1, x, y)[RED_C] - GET_PIXEL(im2, x, y)[RED_C] ) / 255.0;           totalDiff += fabs( GET_PIXEL(im1, x, y)[GREEN_C] - GET_PIXEL(im2, x, y)[GREEN_C] ) / 255.0;           totalDiff += fabs( GET_PIXEL(im1, x, y)[BLUE_C] - GET_PIXEL(im2, x, y)[BLUE_C] ) / 255.0;         }      }      printf("%lf\n", 100.0 * totalDiff / (double)(im1->width * im1->height * 3) );   /* BODY ends */   }   free_img(im1);   free_img(im2);}`

The output on Lenna is:

```1.625587
```

## C++

based upon C version, using Qt 4.4

`#include <QImage>#include <cstdlib>#include <QColor>#include <iostream> int main( int argc , char *argv[ ] ) {   if ( argc != 3 ) {      std::cout << "Call this with imagecompare <file of image 1>" 	 << " <file of image 2>\n" ;      return 1 ;   }   QImage firstImage ( argv[ 1 ] ) ;   QImage secondImage ( argv[ 2 ] ) ;   double totaldiff = 0.0 ; //holds the number of different pixels   int h = firstImage.height( ) ;   int w = firstImage.width( ) ;   int hsecond = secondImage.height( ) ;   int wsecond = secondImage.width( ) ;   if ( w != wsecond || h != hsecond ) {      std::cerr << "Error, pictures must have identical dimensions!\n" ;      return 2 ;   }    for ( int y = 0 ; y < h ; y++ ) {      uint *firstLine = ( uint* )firstImage.scanLine( y ) ;      uint *secondLine = ( uint* )secondImage.scanLine( y ) ;      for ( int x = 0 ; x < w ; x++ ) {	 uint pixelFirst = firstLine[ x ] ;	 int rFirst = qRed( pixelFirst ) ;	 int gFirst = qGreen( pixelFirst ) ;	 int bFirst = qBlue( pixelFirst ) ;	 uint pixelSecond = secondLine[ x ] ;	 int rSecond = qRed( pixelSecond ) ;	 int gSecond = qGreen( pixelSecond ) ;	 int bSecond = qBlue( pixelSecond ) ;	 totaldiff += std::abs( rFirst - rSecond ) / 255.0 ;	 totaldiff += std::abs( gFirst - gSecond ) / 255.0 ;	 totaldiff += std::abs( bFirst -bSecond ) / 255.0 ;      }   }   std::cout << "The difference of the two pictures is " <<      (totaldiff * 100)  / (w * h * 3)  << " % !\n" ;   return 0 ;}`

output on pictures given;

```The difference of the two pictures is 1.62559 % !
```

## C#

`using System;using System.Drawing; class Program{    static void Main()    {        Bitmap img1 = new Bitmap("Lenna50.jpg");        Bitmap img2 = new Bitmap("Lenna100.jpg");         if (img1.Size != img2.Size)        {            Console.Error.WriteLine("Images are of different sizes");            return;        }         float diff = 0;         for (int y = 0; y < img1.Height; y++)        {            for (int x = 0; x < img1.Width; x++)            {                Color pixel1 = img1.GetPixel(x, y);                Color pixel2 = img2.GetPixel(x, y);                 diff += Math.Abs(pixel1.R - pixel2.R);                diff += Math.Abs(pixel1.G - pixel2.G);                diff += Math.Abs(pixel1.B - pixel2.B);            }        }         Console.WriteLine("diff: {0} %", 100 * (diff / 255) / (img1.Width * img1.Height * 3));    }}`

## Common Lisp

This is based upon the C version. Strangely enough, the percentage is 1.77% which is off by about a tenth of a percent.

`(require 'cl-jpeg);;; the JPEG library uses simple-vectors to store data. this is insane!(defun compare-images (file1 file2)  (declare (optimize (speed 3) (safety 0) (debug 0)))  (multiple-value-bind (image1 height width) (jpeg:decode-image file1)    (let ((image2 (jpeg:decode-image file2)))       (loop for i of-type (unsigned-byte 8) across (the simple-vector image1)            for j of-type (unsigned-byte 8) across (the simple-vector image2)            sum (the fixnum (abs (- i j))) into difference of-type fixnum            finally (return (coerce (/ difference width height #.(* 3 255))                                    'double-float))))))   CL-USER> (* 100 (compare-images "Lenna50.jpg" "Lenna100.jpg"))  1.774856467652165d0`

## D

Translation of: Python
`import std.stdio, std.exception, std.range, std.math, bitmap; void main() {    Image!RGB i1, i2;    i1 = i1.loadPPM6("Lenna50.ppm");    i2 = i2.loadPPM6("Lenna100.ppm");     enforce(i1.nx == i2.nx && i1.ny == i2.ny, "Different sizes.");     real dif = 0.0;    foreach (p, q; zip(i1.image, i2.image))        dif += abs(p.r - q.r) + abs(p.g - q.g) + abs(p.b - q.b);     immutable nData = i1.nx * i1.ny * 3;    writeln("Difference (percentage): ",            (dif / 255.0 * 100) / nData);}`
Output:
`Difference (percentage): 1.62559`

## E

By dividing only at the end, we work with integers only as the sum and avoid floating-point error from adding small numbers (per-pixel difference) to large ones (sum of differences).

`def imageDifference(a, b) {  require(a.width() == b.width())  require(a.height() == b.height())  def X := 0..!(a.width())  def Y := 0..!(a.height())   var sumByteDiff := 0  for y in Y {    for x in X {      def ca := a[x, y]      def cb := b[x, y]      sumByteDiff += (ca.rb() - cb.rb()).abs() \                   + (ca.gb() - cb.gb()).abs() \                   + (ca.bb() - cb.bb()).abs()    }    println(y)  }  return sumByteDiff / (255 * 3 * a.width() * a.height())} def imageDifferenceTask() {  println("Read 1...")  def a := readPPM(<import:java.io.makeFileInputStream>(<file:Lenna50.ppm>))  println("Read 2...")  def b := readPPM(<import:java.io.makeFileInputStream>(<file:Lenna100.ppm>))  println("Compare...")  def d := imageDifference(a, b)  println(`\${d * 100}% different.`)}`

The result on the provided images is 1.6255930981604882%.

## F#

` //Percentage difference between 2 images. Nigel Galloway April 18th., 2018let img50 = new System.Drawing.Bitmap("Lenna50.jpg")let img100 = new System.Drawing.Bitmap("Lenna100.jpg")let diff=Seq.cast<System.Drawing.Color*System.Drawing.Color>(Array2D.init img50.Width img50.Height (fun n g->(img50.GetPixel(n,g),img100.GetPixel(n,g))))|>Seq.fold(fun i (e,l)->i+abs(int(e.R)-int(l.R))+abs(int(e.B)-int(l.B))+abs(int(e.G)-int(l.G))) 0printfn "%f" ((float diff)*100.00/(float(img50.Height*img50.Width)*255.0*3.0))`
Output:
```1.774691
```

## Forth

`: pixel-diff ( pixel1 pixel2 -- n )  over 255 and over 255 and - abs >r 8 rshift swap 8 rshift  over 255 and over 255 and - abs >r 8 rshift swap 8 rshift                            - abs r> + r> + ;: bdiff ( bmp1 bmp2 -- fdiff )  2dup bdim rot bdim d<> abort" images not comparable"  0e               ( F: total diff   )  dup bdim * >r    ( R: total pixels )  bdata swap bdata  [email protected] 0 do    over @ over @ pixel-diff 0 d>f f+    cell+ swap cell+  loop 2drop  r> 3 * 255 * 0 d>f f/ ; : .bdiff ( bmp1 bmp2 -- )  cr bdiff 100e f* f. ." percent different" ;`

## Fortran

`program ImageDifference   use RCImageBasic  use RCImageIO   implicit none   integer, parameter :: input1_u = 20, &                        input2_u = 21   type(rgbimage) :: lenna1, lenna2  real           :: totaldiff    open(input1_u, file="Lenna100.ppm", action="read")  open(input2_u, file="Lenna50.ppm", action="read")  call read_ppm(input1_u, lenna1)  call read_ppm(input2_u, lenna2)  close(input1_u)  close(input2_u)   totaldiff = sum(  (abs(lenna1%red - lenna2%red) + &                     abs(lenna1%green - lenna2%green) + &                     abs(lenna1%blue - lenna2%blue)) / 255.0 )    print *, 100.0 * totaldiff / (lenna1%width * lenna1%height * 3.0)   call free_img(lenna1)  call free_img(lenna2) end program ImageDifference`

This gives 1.6555154.

## Frink

` img1 = new image["file:Lenna50.jpg"]img2 = new image["file:Lenna100.jpg"] [w1, h1] = img1.getSize[][w2, h2] = img2.getSize[] sum = 0for x=0 to w1-1   for y=0 to h1-1   {      [r1,g1,b1] = img1.getPixel[x,y]      [r2,g2,b2] = img2.getPixel[x,y]      sum = sum + abs[r1-r2] + abs[g1-g2] + abs[b1-b2]   } errors = sum / (w1 * h1 * 3)println["Error is " + (errors->"percent")] `

This gives an error of approximately 1.625593 percent.

## Go

Using standard image library:

`package main import (    "fmt"    "image/jpeg"    "os"    "log"    "image") func loadJpeg(filename string) (image.Image, error) {    f, err := os.Open(filename)    if err != nil {        return nil, err    }    defer f.Close()     img, err := jpeg.Decode(f)    if err != nil {        return nil, err    }     return img, nil} func diff(a, b uint32) int64 {    if a > b {        return int64(a - b)    }    return int64(b - a)} func main() {    i50, err := loadJpeg("Lenna50.jpg")    if err != nil {        log.Fatal(err)    }     i100, err := loadJpeg("Lenna100.jpg")    if err != nil {        log.Fatal(err)    }     if i50.ColorModel() != i100.ColorModel() {        log.Fatal("different color models")    }     b := i50.Bounds()    if !b.Eq(i100.Bounds()) {        log.Fatal("different image sizes")    }     var sum int64    for y := b.Min.Y; y < b.Max.Y; y++ {        for x := b.Min.X; x < b.Max.X; x++ {            r1, g1, b1, _ := i50.At(x, y).RGBA()            r2, g2, b2, _ := i100.At(x, y).RGBA()            sum += diff(r1, r2)            sum += diff(g1, g2)            sum += diff(b1, b2)        }    }     nPixels := (b.Max.X - b.Min.X) * (b.Max.Y - b.Min.Y)    fmt.Printf("Image difference: %f%%\n",        float64(sum*100)/(float64(nPixels)*0xffff*3))}`

Output:

```Image difference: 1.774785%
```

`package main // Files required to build supporting package raster are found in:// * Bitmap// * Read a PPM file import (    "fmt"    "io"    "os/exec"    "raster") func readJpeg(j string) (b *raster.Bitmap, err error) {    c := exec.Command("convert", j, "ppm:-")    var pipe io.Reader    pipe, err = c.StdoutPipe()    if err != nil {        return    }    err = c.Start()    if err != nil {        return    }    return raster.ReadPpmFrom(pipe)} func main() {    b1, err := readJpeg("Lenna50.jpg")    if err != nil {        fmt.Println(err)        return    }    b2, err := readJpeg("Lenna100.jpg")    if err != nil {        fmt.Println(err)        return    }    b1c, b1r := b1.Extent()    b2c, b2r := b2.Extent()    if b1c != b2c || b1r != b2r {        fmt.Println("image extents not the same")        return    }    var sum int64    for y := 0; y < b1r; y++ {        for x := 0; x < b1c; x++ {            p1, _ := b1.GetPx(x, y)            p2, _ := b2.GetPx(x, y)            d := int64(p1.R) - int64(p2.R)            if d < 0 {                sum -= d            } else {                sum += d            }            d = int64(p1.G) - int64(p2.G)            if d < 0 {                sum -= d            } else {                sum += d            }            d = int64(p1.B) - int64(p2.B)            if d < 0 {                sum -= d            } else {                sum += d            }        }    }    fmt.Printf("Image difference: %f%%\n",        float64(sum)*100/(float64(b1c*b1r)*255*3))}`

Output:

```Image difference: 1.625593%
```

This implementation takes PPMs as input. It uses modules defined in Basic bitmap storage and Write ppm file.

`import Bitmapimport Bitmap.Netpbmimport Bitmap.RGB import Control.Monadimport Control.Monad.STimport System.Environment (getArgs) main = do    [path1, path2] <- getArgs    image1 <- readNetpbm path1    image2 <- readNetpbm path2    diff <- stToIO \$ imageDiff image1 image2    putStrLn \$ "Difference: " ++ show (100 * diff) ++ "%" imageDiff :: Image s RGB -> Image s RGB -> ST s DoubleimageDiff image1 image2 = do      i1 <- getPixels image1      i2 <- getPixels image2      unless (length i1 == length i2) \$          fail "imageDiff: Images are of different sizes"      return \$          toEnum (sum \$ zipWith minus i1 i2) /          toEnum (3 * 255 * length i1)  where (RGB (r1, g1, b1)) `minus` (RGB (r2, g2, b2)) =            abs (r1 - r2) + abs (g1 - g2) + abs (b1 - b2)`

## Icon and Unicon

The images are opened as hidden windows and directly queried for their size and pixel contents. RGB colour intensities range from 0-65535 and all calculations are done with large integers and converted to real at the end. The Icon and Unicon graphics facilities are under documented with respect to some features. Unicon can support reading and writing to a number of additional image formats. I'm not sure if this will run under Icon or not. Some minor reworking of the open would be the minimum requirement; however, Icon may not have read support for jpg files.

`link printf   # for main only procedure main()    # % difference between images   fn1 := "Lenna100.jpg"   fn2 := "Lenna50.jpg"   printf("%%difference of files %i & %i = %r\n",fn1,fn2,ImageDiff(fn1,fn2)) end procedure ImageDiff(fn1,fn2)  #: return % difference of two images   img1 := open(1,"g","canvas=hidden","image="||fn1) | stop("Open failed ",fn1)   img2 := open(2,"g","canvas=hidden","image="||fn2) | stop("Open failed ",fn2)    if WAttrib(img1,"width") ~= WAttrib(img2,"width") |       WAttrib(img1,"height") ~= WAttrib(img2,"height") then          stop("Images must be the same size")    pix1    := create Pixel(img1)  # access pixels one at a time   pix2    := create Pixel(img2)  # ... facilitate interleaved access    sum := pix := 0    while pix +:= 1 & p1 := csv2l(@pix1) & p2 := csv2l(@pix2) do       every sum +:= abs(p1[i := 1 to *p1] - p2[i])     every close(img1|img2)         return sum / (pix * 3 * 65535 / 100. )end procedure csv2l(p)   #: return a list from a comma separated stringL := []p ? until pos(0) do {   put(L,tab(find(",")|0))    move(1)   }return Lend`
Output:
`%difference of files "Lenna100.jpg" & "Lenna50.jpg" = 1.625587`

## J

`   require 'media/image3'   'Lenna50.jpg' (+/@,@:|@:- % 2.55 * */@[email protected]])&read_image 'Lenna100.jpg'1.62559`

## Java

`import java.awt.image.BufferedImage;import java.io.File;import java.io.IOException;import javax.imageio.ImageIO; public enum ImgDiffPercent {    ;     public static void main(String[] args) throws IOException {        // https://rosettacode.org/mw/images/3/3c/Lenna50.jpg        // https://rosettacode.org/mw/images/b/b6/Lenna100.jpg        BufferedImage img1 = ImageIO.read(new File("Lenna50.jpg"));        BufferedImage img2 = ImageIO.read(new File("Lenna100.jpg"));         double p = getDifferencePercent(img1, img2);        System.out.println("diff percent: " + p);    }     private static double getDifferencePercent(BufferedImage img1, BufferedImage img2) {        int width = img1.getWidth();        int height = img1.getHeight();        int width2 = img2.getWidth();        int height2 = img2.getHeight();        if (width != width2 || height != height2) {            throw new IllegalArgumentException(String.format("Images must have the same dimensions: (%d,%d) vs. (%d,%d)", width, height, width2, height2));        }         long diff = 0;        for (int y = 0; y < height; y++) {            for (int x = 0; x < width; x++) {                diff += pixelDiff(img1.getRGB(x, y), img2.getRGB(x, y));            }        }        long maxDiff = 3L * 255 * width * height;         return 100.0 * diff / maxDiff;    }     private static int pixelDiff(int rgb1, int rgb2) {        int r1 = (rgb1 >> 16) & 0xff;        int g1 = (rgb1 >>  8) & 0xff;        int b1 =  rgb1        & 0xff;        int r2 = (rgb2 >> 16) & 0xff;        int g2 = (rgb2 >>  8) & 0xff;        int b2 =  rgb2        & 0xff;        return Math.abs(r1 - r2) + Math.abs(g1 - g2) + Math.abs(b1 - b2);    }}`

## JavaScript

`function getImageData(url, callback) {	var img = document.createElement('img');	var canvas = document.createElement('canvas'); 	img.onload = function () {		canvas.width = img.width;		canvas.height = img.height;		var ctx = canvas.getContext('2d');		ctx.drawImage(img, 0, 0);		callback(ctx.getImageData(0, 0, img.width, img.height));	}; 	img.src = url;} function compare(firstImage, secondImage, callback) {	getImageData(firstImage, function (img1) {		getImageData(secondImage, function (img2) {			if (img1.width !== img2.width || img1.height != img2.height) {				callback(NaN);				return;			} 			var diff = 0; 			for (var i = 0; i < img1.data.length / 4; i++) {				diff += Math.abs(img1.data[4 * i + 0] - img2.data[4 * i + 0]) / 255;				diff += Math.abs(img1.data[4 * i + 1] - img2.data[4 * i + 1]) / 255;				diff += Math.abs(img1.data[4 * i + 2] - img2.data[4 * i + 2]) / 255;			} 			callback(100 * diff / (img1.width * img1.height * 3));		});	});} compare('Lenna50.jpg', 'Lenna100.jpg', function (result) {	console.log(result);});`

## Julia

Works with: Julia version 0.6
`using Images, FileIO absdiff(a::RGB{T}, b::RGB{T}) where T = sum(abs(col(a) - col(b)) for col in (red, green, blue))function pctdiff(A::Matrix{Color{T}}, B::Matrix{Color{T}}) where T    size(A) != size(B) && throw(ArgumentError("images must be same-size"))    s = zero(T)    for (a, b) in zip(A, B)        s += absdiff(a, b)    end    return 100s / 3prod(size(A))end img50  = load("data/lenna50.jpg") |> Matrix{RGB{Float64}};img100 = load("data/lenna100.jpg") |> Matrix{RGB{Float64}}; d = pctdiff(img50, img100)@printf("Percentage difference: %.4f%%\n", d)`
Output:
`Percentage difference: 1.6247%`

## Kotlin

Translation of: Java
`// version 1.2.10 import java.awt.image.BufferedImageimport java.io.Fileimport javax.imageio.ImageIOimport kotlin.math.abs fun getDifferencePercent(img1: BufferedImage, img2: BufferedImage): Double {    val width = img1.width    val height = img1.height    val width2 = img2.width    val height2 = img2.height    if (width != width2 || height != height2) {        val f = "(%d,%d) vs. (%d,%d)".format(width, height, width2, height2)        throw IllegalArgumentException("Images must have the same dimensions: \$f")    }    var diff = 0L    for (y in 0 until height) {        for (x in 0 until width) {            diff += pixelDiff(img1.getRGB(x, y), img2.getRGB(x, y))        }    }    val maxDiff = 3L * 255 * width * height    return 100.0 * diff / maxDiff} fun pixelDiff(rgb1: Int, rgb2: Int): Int {    val r1 = (rgb1 shr 16) and 0xff    val g1 = (rgb1 shr 8)  and 0xff    val b1 =  rgb1         and 0xff    val r2 = (rgb2 shr 16) and 0xff    val g2 = (rgb2 shr 8)  and 0xff    val b2 =  rgb2         and 0xff    return abs(r1 - r2) + abs(g1 - g2) + abs(b1 - b2)} fun main(args: Array<String>) {    val img1 = ImageIO.read(File("Lenna50.jpg"))    val img2 = ImageIO.read(File("Lenna100.jpg"))     val p = getDifferencePercent(img1, img2)    println("The percentage difference is \${"%.6f".format(p)}%")}`
Output:
```The percentage difference is 1.625593%
```

## Liberty BASIC

LB uses here a DLL to allow loading the jpgs. I get the 'other' result if I use LB's native bmp load and convert the jpgs to bmp with the Gimp! The GUI shows the 'difference image'. SceenDisplay

` now =time\$( "seconds")nomainwin WindowWidth  = 1620WindowHeight =  660 open "jpeg.dll" for dll as #j   '   "JPEG.DLL copyright Alyce Watson, 2003. " open "RC Image Comparison- difference shown as 20 times abs( pixel_difference." for graphics_nf_nsb as #1    #1 "trapclose [quit]"    #1 "down ; fill black"     hW =hwnd( #1)    calldll #user32,"GetDC", hW as ulong, hdc as ulong     jname1\$   ="Lenna50.jpg"    hPic1     =LoadImageFile( hW, jname1\$)    if hPic1 =0 then notice "Function failed.": wait    loadbmp "demo1", hPic1    hDemo1 =hbmp( "demo1")    #1 "drawbmp demo1 10 10 ; flush"     jname2\$ ="Lenna100.jpg"    hPic2     =LoadImageFile( hW, jname2\$)    if hPic2 =0 then notice "Function failed.": wait    loadbmp "demo2", hPic2    hDemo1    =hbmp( "demo2")    #1 "drawbmp demo2 550 10 ; flush"     c1 =16777216    c2 =   65536    c3 =     256    x1 =10    y1 =10    x2 =550    y2 =10     for y =0 to 511        for x =0 to 511            pixel1  =( GetPixel( hdc,  x1 +x, y1 +y) + c1) mod c1            b1      = int(  pixel1  /c2)            g1      = int(( pixel1 -b1 *c2) /c3)            r1      = int(  pixel1 -b1 *c2 -g1 *c3)             pixel2  =( GetPixel( hdc, x2 +x, y2 +y) + c1) mod c1            b2      = int(  pixel2  /c2)            g2      = int(( pixel2 -b2 *c2) /c3)            r2      = int(  pixel2 -b2 *c2 -g2 *c3)             totalDiff =totalDiff +abs( r1 -r2) +abs( g1 -g2)+ abs( b1 -b2)             #1 "color "; 20 *abs( r2 -r1); " "; 20 *abs( g2 -g1); " "; 20 *abs( b2 -b1)            #1 "set "; 1090 +x; " "; 10 +y            scan        next x    next y    #1 "place 90 575 ; color white ; backcolor black"   #1 "font courier 9 bold"   #1 "\"; " Difference between images          =";  using( "#.#####", 100.0 *totalDiff / 512 /512 /3 /255); "%."   #1 "\"; " Rosetta Code for these two images  =1.62125%."; "   Time taken ="; time\$( "seconds") -now; " seconds."   #1 "flush" wait function LoadImageFile( hWnd, file\$)    calldll #j,     "LoadImageFile",   hWnd as ulong, file\$ as ptr, LoadImageFile as ulongend function function GetPixel( hDC, x, y)    calldll #gdi32, "GetPixel",        hDC As uLong,  x As long,    y As long,     GetPixel As longend function [quit]    if hPic1  <>0 then calldll #gdi32, "DeleteObject", hPic1 as long, re as long    if hPic2  <>0 then calldll #gdi32, "DeleteObject", hPic2 as long, re as long    if hDemo1 <>0 then unloadbmp "demo1"    if hDemo2 <>0 then unloadbmp "demo2"    close #1    close #j    end `

## Mathematica

`img50 = [email protected][NotebookDirectory[] <> "Lenna50.jpg"];img100 = [email protected][NotebookDirectory[] <> "Lenna100.jpg"];diff = img50 - img100;Print["Total Difference between both Lenas = ",  [email protected]@[email protected]/Times @@ [email protected]*100, "%"]`

Output

`Total Difference between both Lenas = 1.62559%`

## MATLAB

` % Percentage difference between imagesfunction p = PercentageDifferenceBetweenImages(im1,im2) if numel(im1)~=numel(im2),    error('Error: images have to be the same size');end d = abs(single(im1) - single(im2))./255;p = sum(d(:))./numel(im1)*100; disp(['Percentage difference between images is: ', num2str(p), '%'])`

Output

`Percentage difference between images is: 1.6256%`

## MAXScript

`fn diffImages =(	local img1 = selectBitmap caption:"Select Image 1"	local img2 = selectBitmap caption:"Select Image 2"	local totalDiff = 0	for i in 0 to (img1.height-1) do	(		local img1Row = getPixels img1 [0, i] img1.width		local img2Row = getPixels img2 [0, i] img2.width 		for j in 1 to img1.width do		(			totalDiff += (abs (img1Row[j].r - img2Row[j].r)) / 255.0			totalDiff += (abs (img1Row[j].g - img2Row[j].g)) / 255.0			totalDiff += (abs (img1Row[j].b - img2Row[j].b)) / 255.0		)	)	format "Diff: %\%\n" (totalDiff / ((img1.width * img1.height * 3) as float) * 100))`

## OCaml

Library: glMLite
`#! /usr/bin/env ocaml#directory "+glMLite/"#load "jpeg_loader.cma"#load "bigarray.cma"open Jpeg_loader let () =  let img1, width1, height1, col_comp1, color_space1 = load_img (Filename Sys.argv.(1))  and img2, width2, height2, col_comp2, color_space2 = load_img (Filename Sys.argv.(2)) in   assert(width1 = width2);  assert(height1 = height2);  assert(col_comp1 = col_comp2);  (* number of color components *)  assert(color_space1 = color_space2);   let img1 = Bigarray.array3_of_genarray img1  and img2 = Bigarray.array3_of_genarray img2 in   let sum = ref 0.0  and num = ref 0 in   for x=0 to pred width1 do    for y=0 to pred height1 do      for c=0 to pred col_comp1 do        let v1 = float img1.{x,y,c}        and v2 = float img2.{x,y,c} in        let diff = (abs_float (v1 -. v2)) /. 255. in        sum := diff +. !sum;        incr num;      done;    done;  done;   let diff_percent = !sum /. float !num in  Printf.printf " diff: %f percent\n" diff_percent;;;`

## Perl

`use Image::Imlib2; my \$img1 = Image::Imlib2->load('Lenna50.jpg')  || die;my \$img2 = Image::Imlib2->load('Lenna100.jpg') || die; my \$w = \$img1->width;my \$h = \$img1->height; my \$sum = 0; for my \$x (0..\$w-1) {    for my \$y (0..\$h-1) {        my (\$r1, \$g1, \$b1) = \$img1->query_pixel(\$x, \$y);        my (\$r2, \$g2, \$b2) = \$img2->query_pixel(\$x, \$y);        \$sum += abs(\$r1-\$r2) + abs(\$g1-\$g2) + abs(\$b1-\$b2);    }} printf "%% difference = %.4f\n", 100 * \$sum / (\$w * \$h * 3 * 255);`
Output:
`% difference = 1.7747`

Alternative solution:

`use Imager;use List::AllUtils qw(sum pairwise); sub img_diff {    my (\$file1, \$file2) = @_;     my \$img1 = Imager->new(file => \$file1);    my \$img2 = Imager->new(file => \$file2);     my (\$w1, \$h1) = (\$img1->getwidth, \$img1->getheight);    my (\$w2, \$h2) = (\$img2->getwidth, \$img2->getheight);     if (\$w1 != \$w2 or \$h1 != \$h2) {        die "Can't compare images of different sizes";    }     my \$sum = 0;    foreach my \$y (0 .. \$h1 - 1) {        foreach my \$x (0 .. \$w1 - 1) {            my @rgba1 = \$img1->getpixel(x => \$x, y => \$y)->rgba;            my @rgba2 = \$img2->getpixel(x => \$x, y => \$y)->rgba;            \$sum += sum(pairwise { abs(\$a - \$b) } @rgba1, @rgba2);        }    }     \$sum / (\$w1 * \$h1 * 255 * 3);} printf "difference = %f%%\n", 100 * img_diff('Lenna50.jpg', 'Lenna100.jpg');`
Output:
```difference = 1.625593%
```

## Perl 6

`#!/usr/bin/env perl6 use v6;use GD::Raw; # Reference:# https://github.com/dagurval/perl6-gd-raw my \$fh1 = fopen('./Lenna50.jpg', "rb") or die;my \$img1 = gdImageCreateFromJpeg(\$fh1);my \$fh2 = fopen('./Lenna100.jpg', "rb") or die;my \$img2 = gdImageCreateFromJpeg(\$fh2); my \$img1X = gdImageSX(\$img1);my \$img1Y = gdImageSY(\$img1);my \$img2X = gdImageSX(\$img2);my \$img2Y = gdImageSY(\$img2); (\$img1X == \$img2X and \$img1Y == \$img2Y) or die "Image dimensions must match."; my \$diff = 0;my (\$px1, \$px2);loop (my \$i = 0; \$i < \$img1X; \$i++) {   loop (my \$j = 0; \$j < \$img1Y; \$j++) {       \$px1 = gdImageGetPixel(\$img1, \$i, \$j);      \$px2 = gdImageGetPixel(\$img2, \$i, \$j);       \$diff += abs(gdImageRed(\$img1, \$px1) - gdImageRed(\$img2, \$px2));      \$diff += abs(gdImageGreen(\$img1, \$px1) - gdImageGreen(\$img2, \$px2));      \$diff += abs(gdImageBlue(\$img1, \$px1) - gdImageBlue(\$img2, \$px2));   }} say "%difference = ", \$diff/(\$img1X*\$img1Y*3*255)*100; gdImageDestroy(\$img1);gdImageDestroy(\$img2); `
Output:
```%difference = 1.625593098
```

## Phix

`-- demo\rosetta\Percentage_difference_between_images.exwinclude ppm.e function split_colour(integer c)    return sq_div(sq_and_bits(c, {#FF0000,#FF00,#FF}),                                 {#010000,#0100,#01})end function function percentage_diff(sequence img1, img2)    if length(img1)!=length(img2)    or length(img1[1])!=length(img2[1]) then        return "sizes do not match"    end if    atom diff = 0    for i=1 to length(img1) do        for j=1 to length(img1[i]) do            integer {r1,g1,b1} = split_colour(img1[i,j]),                    {r2,g2,b2} = split_colour(img2[i,j])            diff += abs(r1-r2)+abs(g1-g2)+abs(b1-b2)        end for     end for     return 100*diff/(length(img1)*length(img1[1]))/3/255end function sequence img1 = read_ppm("Lenna50.ppm"),         img2 = read_ppm("Lenna100.ppm")?percentage_diff(img1,img2)`
Output:
```1.625593098
```

## PicoLisp

`(call "convert" "Lenna50.jpg" (tmp "Lenna50.ppm"))(call "convert" "Lenna100.jpg" (tmp "Lenna100.ppm")) (let (Total 0  Diff 0)   (in (tmp "Lenna50.ppm")      (in (tmp "Lenna100.ppm")         (while (rd 1)            (inc 'Diff               (*/                  (abs (- @ (in -1 (rd 1))))                  1000000                  255 ) )            (inc 'Total) ) ) )   (prinl "Difference is " (format (*/ Diff Total) 4) " percent") )`

Output:

`Difference is 1.6256 percent`

## PureBasic

This program downloads both jpg files, decodes them & saves them in 2D-arrays for simple comparison which part is comparable with the other languages.

`#URL1="http://rosettacode.org/mw/images/3/3c/Lenna50.jpg"#URL2="http://rosettacode.org/mw/images/b/b6/Lenna100.jpg" Procedure.s GetTempFileName(basename\$="",Extension\$=".tmp")  Protected file\$, i  Repeat: file\$=GetTemporaryDirectory()+basename\$+"_"+Str(i)+Extension\$: i+1  Until FileSize(file\$) = -1 ; E.g. File not found  ProcedureReturn file\$EndProcedure Procedure ImageToMatrix(Image,Array P(2))  Protected Width=ImageWidth(0)-1, Height=ImageHeight(0)-1, x, y  ; Scaling down Width & Height by -1 to compensate for using 0-based arrays  Dim P(Width,Height)  StartDrawing(ImageOutput(Image))  For x=0 To Width    For y=0 To Height      P(x,y)=Point(x,y)    Next y  Next x  StopDrawing()EndProcedure Define File1\$, File2\$, totalDiff, x, y, w, h ; Load the pictures from RoettaCodeInitNetwork()File1\$=GetTempFileName("",".jpg"): ReceiveHTTPFile(#URL1,File1\$)File2\$=GetTempFileName("",".jpg"): ReceiveHTTPFile(#URL2,File2\$) ; Decode the images & clean up temporary filesUseJPEGImageDecoder()LoadImage(0,File1\$):LoadImage(1,File2\$)DeleteFile(File1\$): DeleteFile(File2\$) ; Make two 2D arrays to hold the dataDim Pic1(0,0): Dim Pic2(0,0) ;Load the image data into the matrixesImageToMatrix(0,Pic1()): ImageToMatrix(1,Pic2()) ; Compare the dataw=ArraySize(pic1()): h=ArraySize(pic1(),2)For x=0 To w  For y=0 To h    totalDiff+ Abs(  Red(Pic1(x,y)) -   Red(Pic2(x,y)))    totalDiff+ Abs(Green(Pic1(x,y)) - Green(Pic2(x,y)))    totalDiff+ Abs( Blue(Pic1(x,y)) -  Blue(Pic2(x,y)))  Next yNext x MessageRequester("Result","Diff= "+StrD(100*totalDiff/(255*w*h*3),3)+" %")`

## Python

You must install the Python Imaging Library to use this example.

Works with: python version 3.x
`import Image i1 = Image.open("image1.jpg")i2 = Image.open("image2.jpg")assert i1.mode == i2.mode, "Different kinds of images."assert i1.size == i2.size, "Different sizes." pairs = zip(i1.getdata(), i2.getdata())if len(i1.getbands()) == 1:    # for gray-scale jpegs    dif = sum(abs(p1-p2) for p1,p2 in pairs)else:    dif = sum(abs(c1-c2) for p1,p2 in pairs for c1,c2 in zip(p1,p2)) ncomponents = i1.size[0] * i1.size[1] * 3print "Difference (percentage):", (dif / 255.0 * 100) / ncomponents`
Works with: python version 2.x
`from itertools import izipimport Image i1 = Image.open("image1.jpg")i2 = Image.open("image2.jpg")assert i1.mode == i2.mode, "Different kinds of images."assert i1.size == i2.size, "Different sizes." pairs = izip(i1.getdata(), i2.getdata())if len(i1.getbands()) == 1:    # for gray-scale jpegs    dif = sum(abs(p1-p2) for p1,p2 in pairs)else:    dif = sum(abs(c1-c2) for p1,p2 in pairs for c1,c2 in zip(p1,p2)) ncomponents = i1.size[0] * i1.size[1] * 3print "Difference (percentage):", (dif / 255.0 * 100) / ncomponents`

## Racket

For some reason, the result is around 1.77% and I can't wrap my head about why. (Tom) Note: On OS X I get 1.6192% as the result. (soegaard)

`#lang racket(require racket/draw) (define (percentage-difference bitmap1 bitmap2)  (define width (send bitmap1 get-width))  (define height (send bitmap1 get-height))  (define buffer1 (make-bytes (* width height 4)))  (define buffer2 (make-bytes (* width height 4)))  (send (send bitmap1 make-dc) get-argb-pixels 0 0 width height buffer1)  (send (send bitmap2 make-dc) get-argb-pixels 0 0 width height buffer2)  (/ (* 100.0        (for/fold ((difference 0))          ((i (in-naturals)) (x1 (in-bytes buffer1)) (x2 (in-bytes buffer2)))          (if (zero? (remainder i 4))              difference              (+ difference (abs (- x1 x2))))))     width height 3 256)) (define lenna50 (read-bitmap "lenna50.jpg"))(define lenna100 (read-bitmap "lenna100.jpg")) (percentage-difference lenna50 lenna100) ;-> 1.7749329408009846`

## REBOL

`rebol [	Title: "Percent Image Difference"	URL: http://rosettacode.org/wiki/Percentage_of_difference_between_2_images] ; Load from local storage. Un/comment as preferred.; a: load-image %lenna50.jpg; b: load-image %lenna100.jpg ; Download from rosettacode.org.a: load-image http://rosettacode.org/mw/images/3/3c/Lenna50.jpgb: load-image http://rosettacode.org/mw/images/b/b6/Lenna100.jpg if a/size <> b/size [print "Image dimensions must match."  halt] ; Compute difference. REBOL has built-in image processing as part of; its GUI package that I can take advantage of here: diff: to-image layout/tight [image a effect [difference b]] ; Calculate deviation. I use 'repeat' to rip through the image pixels; (it knows how to deal with images) and sum, then average. Note that; I can treat the image like an array to get number of pixels. t: 0repeat p diff [t: t + p/1 + p/2 + p/3]print rejoin ["Difference: "  100 * t / (255 * 3 * length? diff)  "%"] ; Optional: Since I now have a difference image, I may as well show; it. Use the buttons or keys 'a', 'b' and 'd' to switch between the; various images. flip: func [	"Change to new image and label."	name [word!] "Image to switch to."][x/text: rejoin ["Image " name]  x/image: get name  show x] ; Because the differences between the images are very small, I enhance; the diff with a high contrast to make the result easier to; see. Comment this out for the "pure" image. diff: to-image layout/tight [image diff effect [contrast 100]] view l: layout [	x: image diff	across 	button "a" #"a"          [flip 'a]	button "b" #"b"          [flip 'b]	button "difference" #"d" [flip 'diff]]`

Output:

`Difference: 1.62559309816049%`

Note that this image has been contrast enhanced to highlight the differences.

## Ruby

uses the `raster_graphics` library

`require 'raster_graphics' class RGBColour  # the difference between two colours  def -(a_colour)    (@red - a_colour.red).abs +    (@green - a_colour.green).abs +    (@blue - a_colour.blue).abs  endend class Pixmap  # the difference between two images  def -(a_pixmap)    if @width != a_pixmap.width or @height != a_pixmap.height      raise ArgumentError, "can't compare images with different sizes"    end    sum = 0    each_pixel {|x,y| sum += self[x,y] - a_pixmap[x,y]}    Float(sum) / (@width * @height * 255 * 3)  endend lenna50 = Pixmap.open_from_jpeg('Lenna50.jpg')lenna100 = Pixmap.open_from_jpeg('Lenna100.jpg') puts "difference: %.5f%%" % (100.0 * (lenna50 - lenna100))`

produces:

`difference: 1.62559%`

## Sidef

`require('Imager') func img_diff(a, b) {     func from_file(name) {         %s|Imager|.new(file => name)    }     func size(img) {        (img.getwidth, img.getheight)    }     func pixel_diff(p1, p2) {        [p1.rgba] »-« [p2.rgba] -> map { .abs }.sum    }     func read_pixel(img, x, y) {        img.getpixel(x => x, y => y)    }     var(img1, img2) = (from_file(a), from_file(b))     var(w1, h1) = size(img1)    var(w2, h2) = size(img2)     if ((w1 != w2) || (h1 != h2)) {        return nil    }     var sum = 0    for y,x in (^h1 ~X ^w1) {        sum += pixel_diff(read_pixel(img1, x, y), read_pixel(img2, x, y))    }     sum / (w1 * h1 * 255 * 3)} say 100*img_diff('Lenna50.jpg', 'Lenna100.jpg')`
Output:
```1.62559309816048815359477124183007
```

## Swift

`func pixelValues(fromCGImage imageRef: CGImage?) -> [UInt8]?{    var width = 0    var height = 0    var pixelValues: [UInt8]?     if let imageRef = imageRef {        width = imageRef.width        height = imageRef.height        let bitsPerComponent = imageRef.bitsPerComponent        let bytesPerRow = imageRef.bytesPerRow        let totalBytes = height * bytesPerRow        let bitmapInfo = imageRef.bitmapInfo         let colorSpace = CGColorSpaceCreateDeviceRGB()        var intensities = [UInt8](repeating: 0, count: totalBytes)         let contextRef = CGContext(data: &intensities,                                  width: width,                                 height: height,                       bitsPerComponent: bitsPerComponent,                            bytesPerRow: bytesPerRow,                                  space: colorSpace,                             bitmapInfo: bitmapInfo.rawValue)        contextRef?.draw(imageRef, in: CGRect(x: 0.0, y: 0.0, width: CGFloat(width), height: CGFloat(height)))         pixelValues = intensities    }     return pixelValues} func compareImages(image1: UIImage, image2: UIImage) -> Double? {    guard let data1 = pixelValues(fromCGImage: image1.cgImage),        let data2 = pixelValues(fromCGImage: image2.cgImage),        data1.count == data2.count else {            return nil    }     let width = Double(image1.size.width)    let height = Double(image1.size.height)     return zip(data1, data2)        .enumerated()        .reduce(0.0) {            \$1.offset % 4 == 3 ? \$0 : \$0 + abs(Double(\$1.element.0) - Double(\$1.element.1))        }        * 100 / (width * height * 3.0) / 255.0} let image1 = UIImage(named: "Lenna50")let image2 = UIImage(named: "Lenna100") compareImages(image1: image1, image2: image2)  `

## Tcl

Library: Tk

This version uses the Img package, but only to provide a convenient JPEG loader; it's utterly unnecessary for the process of actually computing the difference.

`package require Tk proc imageDifference {img1 img2} {    if {	[image width \$img1] != [image width \$img2] ||	[image height \$img1] != [image height \$img2]    } then {	return -code error "images are different size"    }    set diff 0    for {set x 0} {\$x<[image width \$img1]} {incr x} {	for {set y 0} {\$y<[image height \$img1]} {incr y} {	    lassign [\$img1 get \$x \$y] r1 g1 b1	    lassign [\$img2 get \$x \$y] r2 g2 b2	    incr diff [expr {abs(\$r1-\$r2)+abs(\$g1-\$g2)+abs(\$b1-\$b2)}]	}    }    expr {\$diff/double(\$x*\$y*3*255)}} # Package only used for JPEG loaderpackage require Imgimage create photo lenna50 -file lenna50.jpgimage create photo lenna100 -file lenna100.jpgputs "difference is [expr {[imageDifference lenna50 lenna100]*100.}]%"exit ;# Need explicit exit here; don't want a GUI`

It produces this output:

```difference is 1.6255930981604882%
```

## Vedit macro language

This implementation compares two BMP images.

`Chdir("|(USER_MACRO)\Rosetta\data")File_Open("Lenna50.bmp", BROWSE)#10 = Buf_Num				// #10 = buffer for 1st imageFile_Open("Lenna100.bmp", BROWSE)#20 = Buf_Num				// #20 = buffer for 2nd image Goto_Pos(10)  				// offset to pixel dataGoto_Pos(Cur_Char + Cur_Char(1)*256)Buf_Switch(#10)Goto_Pos(10)Goto_Pos(Cur_Char + Cur_Char(1)*256) #15 = 0					// #15 = difference#16 = 0					// #16 = total number of samplesWhile(!At_EOF) {    #11 = Cur_Char; Char    Buf_Switch(#20)    #21 = Cur_Char; Char    #15 += abs(#11-#21)    #16++    Buf_Switch(#10)} #19 = #15 / (#16*256/100000)M("Sum of diff: ") NT(#15)M("Total bytes: ") NT(#16)M("Difference:  ") NT(#19/1000,LEFT+NOCR) M(".") NT(#19%1000,LEFT+NOCR) M("%\n") Buf_Switch(#10) Buf_Quit(OK)Buf_Switch(#20) Buf_Quit(OK)`

Output, when comparing the Lenna images that were converted to BMP:

```Sum of diff: 3259967
Total bytes: 786432
Difference:  1.619%
```

## zkl

Uses the PPM class from http://rosettacode.org/wiki/Bitmap/Bresenham%27s_line_algorithm#zkl

`fcn imageDiff(img1,img2){   if(img1.w!=img2.w or img1.h!=img2.h)      throw(Exception.ValueError("width/height of the images must match!"));   img1.data.howza(0).walker().zip(img2.data.howza(0)) // lazy bytes, not strings   .reduce(fcn(totalDiff,[(a,b)]){ totalDiff + (a - b).abs() },0)   .toFloat()/img1.w/img1.h/3/255; // or: .toFloat()/img1.data.len()/255}`

Take the bytes in each image, zip them together [lazily], sum the differences between each byte and normalize.

`fcn readJPG2PPM(fileName){   p:=System.popen("convert \"%s\" ppm:-".fmt(fileName),"r");      img:=PPM.readPPM(p);   p.close();   img}`

Use the convert utility from ImageMagick to convert a JPEG image to PPM.

`imageDiff(readJPG2PPM("lenna50.jpg"),readJPG2PPM("lenna100.jpg")) :"Image difference = %f%%".fmt(_*100).println();`

Compute the diff between the two Lennas, format and print it. More conventionally, this would be written as

`println("Image difference = %f%%".fmt(   imageDiff(readJPG2PPM("lenna50.jpg"),readJPG2PPM("lenna100.jpg")) * 100));`
Output:
```512  512  # verbiage from convert
512  512
Image difference = 1.624730%
```