Talk:Grayscale image
Linear color space
If I am not wrong, the equation L = 0.2126·R + 0.7152·G + 0.0722·B only works correctly in linear color space. Most images, however, are stored in sRGB color space. If you want to do the conversion correctly for a real world image, you should first convert it into linear color space.
But for simplicity, I guess, we could assume that the image is already in linear color space (even if it actually would require at least 16 bit color depth instead of 8 bit). --PauliKL 17:00, 15 January 2009 (UTC)
- The "parent" task is silent about the color model. If you want to fix it in this way or another, I think, you should better start there.
- Surely we could define some additional tasks dealing with different color models and conversions between them. I am not sure that this would meet much interest.
- Thinking further in this direction, there are so many areas in image processing / computer graphics, that I seriously doubt if RC would ever able to represent more than just a fraction of. Especially because most of them quickly grow out of "boy" format. I wished to add image segmenting tasks, by region growing, by pyramid etc, but then I realized that already this would be far over the top... --Dmitry-kazakov 18:33, 15 January 2009 (UTC)
- Color models are not relevant in the parent task. Creating a storage for image and plotting pixels do not care about color models. Color models are needed when doing conversions, such as RGB to grayscale conversion.
- How so? Color points are kept in a definite model. When plotted the device expects images in a certain format which includes color model specification as well. --Dmitry-kazakov 17:11, 16 January 2009 (UTC)
- The point is that the CIE conversion function mentioned requires linear color mode. If linear color model is not used, you could use just about any weighting factors for R, G and B, and it does not help to use so many decimal digits. A common function used in sRGB color space is L = 0.3*R + 0.59*G + 0.11*B . When this is applied to and sRGB image, the results are closer to CIE conversion than when you use the CIE function in sRGB color space. I just thought that this should be mentioned, in case someone is planning to use the code examples given here in a real application.
- Another commonly overlooked fact is that most image processing functions such as resizing only work correctly in linear color space. But that is another story.
- --PauliKL 16:00, 16 January 2009 (UTC)
- No, they work in any model, of course. It is so that the algorithm depends on the model, obviously. --Dmitry-kazakov 17:11, 16 January 2009 (UTC)