Color of a screen pixel
You are encouraged to solve this task according to the task description, using any language you may know.
Get color information from an arbitrary pixel on the screen, such as the current location of the mouse cursor. The mouse cursor may or may not have to be active in a GUI created by your program. These functions are OS related.
App Inventor
App Inventor has two Canvas blocks to determine the color under a pixel.
GetBackgroundPixelColor returns a color from the Canvas but ignores Ball sprites and ImageSprites.
GetPixelColor returns a color from either the Canvas or a Ball sprite or ImageSprite.
In the app's display below, the purple Ball sprite was touched on the left canvas, but the pixel color (green) returned was from the area below it.
<VIEW THE BLOCKS AND ANDROID APP DISPLAY>
Applesoft BASIC
Low-Resolution (Lo-Res) graphics 40x48, 16 colors, page 1 <lang Applesoft BASIC>X = PDL (0) * 5 / 32 Y = PDL (1) * 3 / 16
COLOR= SCRN( X,Y)</lang>
Hi-Resolution (Hi-Res) graphics 280x192, 6 colors
There is no HSCRN( X,Y) function in Applesoft. What follows is an elaborate subroutine that determines the hi-res color at the location given by variables X and Y on the current hi-res page. A color value in the range from 0 to 7 is returned in the variable C. The color is determined by peeking at adjacent pixels and the Most Significant Bit MSB. The VTAB routine is used as an aid to calculate the address of pixels. Other colors beyond the 6 hi-res colors can be displayed by positioning pixels at byte boundaries using the MSB. This routine is limited to the eight hi-res colors.
<lang Applesoft BASIC>
100 REM GET HCOLOR 110 REM PARAMETERS: X Y 120 REM RETURNS: C 130 REM 140 P = 0:X = X + 1 150 ON (X < 280) GOSUB 300 160 PR = P:P = 0:X = X - 2 170 ON (X > = 0) GOSUB 300 180 PL = P:X = X + 1: GOSUB 300 190 ODD = X - INT (X / 2) * 2 200 C = H * 4 210 IF NOT ((PL = PR) AND (PL < > P)) THEN C = C + P * 3: RETURN 220 IF ODD THEN P = NOT P 230 C = C + P + 1 240 RETURN 250 REM 260 REM GET PIXEL 270 REM PARAMETERS: X Y 280 REM RETURNS: H P 290 REM 300 H = INT (X / 7) 310 V = INT (Y / 8) 320 VO = PEEK (37) 330 HO = PEEK (36) 340 VTAB V + 1: HTAB 1 350 A = PEEK (41) * 256 360 A = A + PEEK (40) + H 370 VTAB VO + 1: HTAB HO + 1 380 A = A + 8192 - 1024 390 P = PEEK (230) / 32 400 IF P = 2 THEN A = A + 8192 410 A = A + (Y - V * 8) * 1024 420 B = X - H * 7 430 V = PEEK (A) 440 H = INT (V / 128) 450 V = INT (V / (2 ^ B)) 460 P = V - INT (V / 2) * 2 470 RETURN
X = 267 : Y = 166 : GOSUB 100 HCOLOR= C </lang>
AutoHotkey
<lang AutoHotkey>PixelGetColor, color, %X%, %Y%</lang>
AutoIt
<lang autoit>Opt('MouseCoordMode',1) ; 1 = (default) absolute screen coordinates $pos = MouseGetPos() $c = PixelGetColor($pos[0], $pos[1]) ConsoleWrite("Color at x=" & $pos[0] & ",y=" & $pos[1] & _ " ==> " & $c & " = 0x" & Hex($c) & @CRLF)</lang>
- Output:
Color at x=3,y=733 ==> 3829413 = 0x003A6EA5
Axe
<lang axe>Disp pxl-Test(50,50)▶Dec,i</lang>
BASIC
In a graphics mode (for instance, SCREEN 13 or SCREEN 12) <lang qbasic>color = point(x, y)</lang>
BBC BASIC
In BBC BASIC for Windows you can read either the 'logical colour' (palette index) or the 'true colour' (24-bit RGB value). <lang bbcbasic> palette_index% = POINT(x%, y%)
RGB24b_colour% = TINT(x%, y%)</lang>
C
<lang c>
- include <X11/Xlib.h>
void get_pixel_color (Display *d, int x, int y, XColor *color) {
XImage *image; image = XGetImage (d, RootWindow (d, DefaultScreen (d)), x, y, 1, 1, AllPlanes, XYPixmap); color->pixel = XGetPixel (image, 0, 0); XFree (image); XQueryColor (d, DefaultColormap(d, DefaultScreen (d)), color);
}
// Your code XColor c; get_pixel_color (display, 30, 40, &c); printf ("%d %d %d\n", c.red, c.green, c.blue); </lang>
(Linux users, see grabc.) <lang c>#include <Windows.h>
COLORREF getColorAtCursor(void) {
POINT p; COLORREF color; HDC hDC; BOOL b;
/* Get the device context for the screen */ hDC = GetDC(NULL); if (hDC == NULL) return CLR_INVALID;
/* Get the current cursor position */ b = GetCursorPos(&p); if (!b) return CLR_INVALID;
/* Retrieve the color at that position */ color = GetPixel(hDC, p.x, p.y);
/* Release the device context again */ ReleaseDC(GetDesktopWindow(), hDC);
return color;
}</lang>
C#
<lang csharp>using System; using System.Drawing; using System.Windows.Forms;
class Program {
static Color GetPixel(Point position) { using (var bitmap = new Bitmap(1, 1)) { using (var graphics = Graphics.FromImage(bitmap)) { graphics.CopyFromScreen(position, new Point(0, 0), new Size(1, 1)); } return bitmap.GetPixel(0, 0); } }
static void Main() { Console.WriteLine(GetPixel(Cursor.Position)); }
}</lang> Sample output: <lang>Color [A=255, R=243, G=242, B=231]</lang>
Clojure
<lang lisp>(defn get-color-at [x y]
(.getPixelColor (java.awt.Robot.) x y))</lang>
Common Lisp
Using Allegro and their Common Graphics package <lang lisp>(in-package :cg-user)
(defun print-hex (n)
(let ((*print-base* 16.) (*print-radix* t)) (print n)) t)
(defun get-byte (n byte)
(logand (ash n (* byte -8)) #xFF))
(defun get-pixel (x y)
(let ((pixval (caar (contents (get-screen-pixmap :box (make-box x y (+ x 1) (+ y 1))))))) (mapcar #'(lambda (i) (get-byte pixval i)) '(2 1 0 3))))
(defun get-mouse-pixel ()
(let ((pos (cursor-position (screen *system*)))) (get-pixel (position-x pos) (position-y pos))))
(print-hex (get-mouse-pixel))</lang>
Sample output: (values are in RGBA order): <lang lisp>(#xe0 #x43 #x43 #xff)</lang>
Delphi
<lang Delphi> program ScreenPixel;
{$APPTYPE CONSOLE}
uses
Windows, SysUtils, Graphics;
// Use this function in a GUI application to return the color
function GetPixelColourAsColor(const PixelCoords: TPoint): TColor;
var
dc: HDC;
begin
// Get Device Context of windows desktop dc := GetDC(0); // Read the color of the pixel at the given coordinates Result := GetPixel(dc,PixelCoords.X,PixelCoords.Y);
end;
// Use this function to get a string representation of the current colour function GetPixelColourAsString(const PixelCoords: TPoint): string; var
r,g,b: Byte; col: TColor;
begin
col := GetPixelColourAsColor(PixelCoords);
// Convert the Delphi TColor value to it's RGB components r := col and $FF; g := (col shr 8) and $FF; b := (col shr 16) and $FF;
// Format the result Result := 'R('+IntToStr(r)+') G('+IntToStr(g)+') G('+IntToStr(b)+')';
{ Alternatively, format the result as follows to get a string representation of the Delphi TColor value
Result := ColorToString(GetPixel(dc,curP.X,curP.Y)); }
end;
var
s: string; P: TPoint;
begin
s := ;
Writeln('Move mouse over a pixel. Hit return to get colour of selected pixel.');
repeat Readln(s); if s = then begin GetCursorPos(P); Writeln('Colour at cursor position X:'+ IntToStr(P.X)+' Y:'+ IntToStr(P.Y) +' = '+ GetPixelColourAsString(P) ); Writeln(); Writeln('Move mouse and hit enter again.'); end; until SameText(s,'quit');
end. </lang>
Example output:
Move mouse over a pixel. Hit return to get colour of selected pixel. Colour at cursor position X:429 Y:161 = R(0) G(0) B(0) Move mouse and hit enter again. Colour at cursor position X:942 Y:358 = R(182) G(206) B(231) Move mouse and hit enter again. Colour at cursor position X:704 Y:103 = R(240) G(240) B(240) Move mouse and hit enter again. Colour at cursor position X:2756 Y:59 = R(250) G(196) B(182)
FreeBASIC
This is a very simple example from the FreeBASIC documentation. To obtain the color of an arbitrary screen pixel (i.e. outside the graphics screen controlled by FB) one would need to use API functions. <lang freebasic>FB 1.05.0 Win64
' Set an appropriate screen mode - 320 x 240 x 8bpp indexed color ScreenRes 320, 240, 8
' Draw a line using color 12 (light red) Line (20,20)-(100,100), 12
' Print the color of a point on the line Print Point(20,20) prints 12
' Sleep before the program closes Sleep</lang>
F#
<lang fsharp>open System.Drawing open System.Windows.Forms
let GetPixel x y =
use img = new Bitmap(1,1) use g = Graphics.FromImage(img) g.CopyFromScreen(new Point(x,y), new Point(0,0), new Size(1,1)) let clr = img.GetPixel(0,0) (clr.R, clr.G, clr.B)
let GetPixelAtMouse () =
let pt = Cursor.Position GetPixel pt.X pt.Y</lang>
C++/CLI
<lang cpp> using namespace System; using namespace System::Drawing; using namespace System::Windows::Forms;
[STAThreadAttribute] int main() { Point^ MousePoint = gcnew Point(); Control^ TempControl = gcnew Control(); MousePoint = TempControl->MousePosition; Bitmap^ TempBitmap = gcnew Bitmap(1,1); Graphics^ g = Graphics::FromImage(TempBitmap); g->CopyFromScreen((Point)MousePoint, Point(0, 0), Size(1, 1)); Color color = TempBitmap->GetPixel(0,0); Console::WriteLine("R: "+color.R.ToString()); Console::WriteLine("G: "+color.G.ToString()); Console::WriteLine("B: "+color.B.ToString()); } </lang>
Integer BASIC
See Applesoft BASIC.
Icon and Unicon
Icon and Unicon don't have direct access to the screen; however, we can read the colour of of a maximal sized window instead. The graphics procedure generates all pixels from a rectangular selection as a comma separated string with RGB values. <lang Icon>link graphics,printf
procedure main()
WOpen("canvas=hidden") # hide for query height := WAttrib("displayheight") - 45 # adjust for ... width := WAttrib("displaywidth") - 20 # ... window 7 borders WClose(&window) W := WOpen("size="||width||","||height,"bg=black") | stop("Unable to open window") every 1 to 10 do { # generate some random rectangles within the frame x := ?width y := ?(height-100) WAttrib("fg="||?["red","green","blue","purple","yellow"]) FillRectangle(x,x+50,y,y+50) } while Event() do printf("x=%d,y=%d pixel=%s\n",&x,&y,Pixel(&x,&y,&x,&y)) WDone(W) # q to exit
end </lang>
graphics.icn provides graphics printf.icn provides printf
Sample Output:
x=943,y=946 pixel=0,0,65535 x=658,y=610 pixel=47802,0,65535 x=934,y=487 pixel=0,0,0
Java
<lang java>public static Color getColorAt(int x, int y){
return new Robot().getPixelColor(x, y);
}</lang>
Kotlin
<lang scala>import java.awt.*
fun getMouseColor(): Color {
val location = MouseInfo.getPointerInfo().location return getColorAt(location.x, location.y)
}
fun getColorAt(x: Int, y: Int): Color {
return Robot().getPixelColor(x, y)
}</lang>
Liberty BASIC
<lang lb>'This example requires the Windows API Struct point, x As long, y As long
hDC = GetDC(0) result = GetCursorPos() Print GetPixel(hDC, point.x.struct, point.y.struct) Call ReleaseDC 0, hDC End
Sub ReleaseDC hWnd, hDC CallDLL #user32,"ReleaseDC", hWnd As uLong, hDC As uLong, ret As Long End Sub
Function GetDC(hWnd) CallDLL #user32, "GetDC", hWnd As uLong, GetDC As uLong End Function
Function GetCursorPos() CallDLL #user32, "GetCursorPos", point As struct, GetCursorPos As uLong End Function
Function GetPixel(hDC, x, y) CallDLL #gdi32, "GetPixel", hDC As uLong, x As long, y As long, GetPixel As long End Function</lang>
Lingo
<lang lingo>on getScreenPixelColor (x, y)
sx = xtra("ScrnXtra3").new() img = sx.ScreenToImage(rect(x, y, x+1, y+1)) return img.getPixel(0, 0)
end</lang>
Locomotive Basic
<lang locobasic>10 x=320:y=200 20 color=TEST(x,y) 30 PRINT "Pen color at"; x; y; "is"; color</lang>
Logo
CLEARSCREEN SHOW PIXEL [255 255 255]
Nim
<lang nim>import gtk2, gdk2, gdk2pixbuf gtk2.nim_init()
proc getPixelColor(x, y: int32): auto =
var p = pixbufNew(COLORSPACE_RGB, false, 8, 1, 1) discard p.getFromDrawable(getDefaultRootWindow().Drawable, getDefaultScreen().getSystemColormap(), x, y, 0, 0, 1, 1) result = cast[tuple[r, g, b: uint8]](p.getPixels[])
echo getPixelColor(0, 0)</lang>
Phix
<lang Phix>integer {r,g,b} = im_pixel(image, x, y)</lang> An example of this in use can be found in demo/pGUI/simple_paint.exw
PHP
<lang php>$img = imagegrabscreen(); $color = imagecolorat($im, 10, 50); imagedestroy($im);</lang>
PicoLisp
Using 'grabc' as recommended in the C solution <lang PicoLisp>(in '(grabc)
(mapcar hex (cdr (line NIL 1 2 2 2))) )</lang>
Output:
73,61,205 -> (73 61 205)
PureBasic
Return the color used at the x,y position in the current output. If the current output has an alpha channel then the result will be a 32bit RGBA value, otherwise it will be a 24bit RGB value. The color can be split in their RGB and alpha values by using the Red(), Green(), Blue() and Alpha() functions.
<lang PureBasic>Color = Point(x, y)</lang>
To get the colour of a pixel on the screen when it is not managed by PureBasic (ie. from other programs' windows), it is necessary to use Windows API. This works only under Windows. <lang PureBasic> hDC = GetDC_(0) Color = GetPixel_(hDC, x, y) ReleaseDC_(0, hDC)</lang>
This work fine!!
<lang PureBasic>poz.point If OpenWindow(0,0,0,100,45,"Get pixel color at cursor position",#PB_Window_MinimizeGadget)
TextGadget(0,0,0,50,12,"Red: ") TextGadget(1,0,15,50,12,"Green: ") TextGadget(2,0,30,50,12,"Blue: ") TextGadget(3,50,0,50,12,"") TextGadget(4,50,15,50,12,"") TextGadget(5,50,30,50,12,"") hDC = GetDC_(0) Repeat oldx=poz\x oldy=poz\y
GetCursorPos_(@poz) Color = GetPixel_(hDC, poz\x, poz\y) If poz\x<>oldx Or poz\y<>oldy
SetGadgetText(3,Str(Red(color))) SetGadgetText(4,Str(Green(color))) SetGadgetText(5,Str(Blue(color)))
EndIf event=WaitWindowEvent(200) Until event=#PB_Event_CloseWindow ReleaseDC_(0, hDC) EndIf</lang>
Python
<lang python>def get_pixel_colour(i_x, i_y): import win32gui i_desktop_window_id = win32gui.GetDesktopWindow() i_desktop_window_dc = win32gui.GetWindowDC(i_desktop_window_id) long_colour = win32gui.GetPixel(i_desktop_window_dc, i_x, i_y) i_colour = int(long_colour) return (i_colour & 0xff), ((i_colour >> 8) & 0xff), ((i_colour >> 16) & 0xff)
print get_pixel_colour(0, 0)</lang>
only
<lang python>def get_pixel_colour(i_x, i_y): import PIL.ImageGrab return PIL.ImageGrab.grab().load()[i_x, i_y]
print get_pixel_colour(0, 0)</lang>
<lang python>def get_pixel_colour(i_x, i_y): import PIL.Image # python-imaging import PIL.ImageStat # python-imaging import Xlib.display # python-xlib o_x_root = Xlib.display.Display().screen().root o_x_image = o_x_root.get_image(i_x, i_y, 1, 1, Xlib.X.ZPixmap, 0xffffffff) o_pil_image_rgb = PIL.Image.fromstring("RGB", (1, 1), o_x_image.data, "raw", "BGRX") lf_colour = PIL.ImageStat.Stat(o_pil_image_rgb).mean return tuple(map(int, lf_colour))
print get_pixel_colour(0, 0)</lang>
<lang python>def get_pixel_colour(i_x, i_y): import gtk # python-gtk2 o_gdk_pixbuf = gtk.gdk.Pixbuf(gtk.gdk.COLORSPACE_RGB, False, 8, 1, 1) o_gdk_pixbuf.get_from_drawable(gtk.gdk.get_default_root_window(), gtk.gdk.colormap_get_system(), i_x, i_y, 0, 0, 1, 1) return tuple(o_gdk_pixbuf.get_pixels_array().tolist()[0][0])
print get_pixel_colour(0, 0)</lang>
<lang python>def get_pixel_colour(i_x, i_y): import PyQt4.QtGui # python-qt4 app = PyQt4.QtGui.QApplication([]) long_qdesktop_id = PyQt4.QtGui.QApplication.desktop().winId() long_colour = PyQt4.QtGui.QPixmap.grabWindow(long_qdesktop_id, i_x, i_y, 1, 1).toImage().pixel(0, 0) i_colour = int(long_colour) return ((i_colour >> 16) & 0xff), ((i_colour >> 8) & 0xff), (i_colour & 0xff)
print get_pixel_colour(0, 0)</lang>
Racket
See get-pixel-color.rkt.
Ring
<lang ring> Load "guilib.ring" new qApp {
win1 = new qWidget() { setWindowTitle("Test using Event Filter!") setGeometry(100,100,400,400) setmousetracking(true) myfilter = new qallevents(win1) myfilter.setKeyPressEvent("pWork()") myfilter.setMouseButtonPressevent("pClick()") myfilter.setmousemoveevent("pMove()")
installeventfilter(myfilter) show() } exec()
}
func pWork
win1.setwindowtitle('KeyPress! : ' + myfilter.getkeycode())
func pClick
new qmessagebox(win1) { setgeometry(100,100,400,100) setwindowtitle("click event!") settext("x : " + myfilter.getx() + " y : " + myfilter.gety() + " button : " + myfilter.getbutton() ) show() }
func pMove
win1.setwindowtitle("Mouse Move , X : " + myfilter.getx() + " Y : " + myfilter.gety() )
</lang> Output:
Ruby
This example requires ImageMagick >= 6.2.10 (works on X11, unsure about other platforms).
<lang ruby>module Screen
IMPORT_COMMAND = '/usr/bin/import'
# Returns an array with RGB values for the pixel at the given coords def self.pixel(x, y) if m = `#{IMPORT_COMMAND} -silent -window root -crop 1x1+#{x.to_i}+#{y.to_i} -depth 8 txt:-`.match(/\((\d+),(\d+),(\d+)\)/) m[1..3].map(&:to_i) else false end end
end</lang>
Scala
<lang Scala>def getColorAt(x: Int, y: Int): Color = new Robot().getPixelColor(x, y)</lang>
Tcl
Works only on X11 or OSX with Xquartz. <lang tcl>package require Tcl 8.5 package require Tk
- Farm out grabbing the screen to an external program.
- If it was just for a Tk window, we'd use the tkimg library instead
proc grabScreen {image} {
set pipe [open {|xwd -root -silent | convert xwd:- ppm:-} rb] $image put [read $pipe] close $pipe
}
- Get the RGB data for a particular pixel (global coords)
proc getPixelAtPoint {x y} {
set buffer [image create photo] grabScreen $buffer set data [$image get $x $y] image delete $buffer return $data
}
- Demo...
puts [format "pixel at mouse: (%d,%d,%d)" \
{*}[getPixelAtPoint {*}[winfo pointerxy .]]]</lang>
TI-89 BASIC
Only the graph screen can be read.
<lang ti89b>pxlTest(y, x) © returns boolean</lang>
Visual Basic .NET
<lang vbnet> Private Function GetPixelColor(ByVal Location As Point) As Color
Dim b As New Bitmap(1, 1) Dim g As Graphics = Graphics.FromImage(b)
g.CopyFromScreen(Location, Point.Empty, New Size(1, 1))
Return b.GetPixel(0, 0)
End Function</lang>
XPL0
Color gets either 1, 2, 4, 8, 15, 16, or 24 significant bits depending on the current graphic mode enabled on an IBM-PC compatible machine with VESA graphics.
<lang XPL0>code ReadPix=44; int Color, X, Y; Color:= ReadPix(X, Y);</lang>
ZX Spectrum Basic
The built-in function POINT (x,y)
returns 0 if the pixel at x,y is set to the relevant PAPER
colour, or 1 if it is set to the INK
colour. (Note that there can only be a maximum of two colours in each 8x8-pixel section of the screen.)
- Programming Tasks
- GUI
- Testing
- App Inventor
- Applesoft BASIC
- AutoHotkey
- AutoIt
- Axe
- BASIC
- BBC BASIC
- C
- Xlib
- C sharp
- Clojure
- Common Lisp
- Delphi
- FreeBASIC
- F Sharp
- C++/CLI
- Integer BASIC
- Icon
- Unicon
- Icon Programming Library
- Java
- Robot
- Kotlin
- Liberty BASIC
- Lingo
- ScrnXtra3 Xtra
- Locomotive Basic
- Logo
- Nim
- GTK2
- Phix
- PGUI
- PHP
- GD
- PicoLisp
- PureBasic
- Python
- PyWin32
- PIL
- Python-xlib
- PyGTK
- PyQt
- Racket
- Ring
- Ruby
- Scala
- Tcl
- Tk
- TI-89 BASIC
- Visual Basic .NET
- XPL0
- ZX Spectrum Basic
- ACL2/Omit
- AWK/Omit
- Batch File/Omit
- Blast/Omit
- Brainf***/Omit
- GUISS/Omit
- Lilypond/Omit
- Logtalk/Omit
- Lotus 123 Macro Scripting/Omit
- Maxima/Omit
- MUMPS/Omit
- PARI/GP/Omit
- PostScript/Omit
- R/Omit
- TPP/Omit
- UNIX Shell/Omit