Legacy ImageMagick Discussions Archive

Most image processing algorithms require a linear colorspace for optimal results. Only when an image is displayed to a monitor or printer does it make sense to utilize gamma. So the ideal workflow would be to store your image in a linear colorspace, Good discussion! Absolutely, let's store it as ...

However, as mentioned, pushing the pixels to an image format is problematic since most formats do not have sufficient metadata to decide if the grayscale is linear or non-linear (excepting MIFF and MPC). It shouldn't be any more problematic for Gray (*Luma vs *Luminance intensity) than it is for ...

"-colorspace Gray" seems to create a nonlinear grayscale (in fact same as -grayscale rec709luma) by default in IM7. Under what circumstances is gray assumed linear? In fact I've documented what I've observed to be the behavior of grayscale images with respect to "-intensity" as a proposed update to ...

The documentation is right. Gray is assumed linear. Likely a bug. We are investigating a fix to the problem and documentation now. "-colorspace Gray" seems to create a nonlinear grayscale (in fact same as -grayscale rec709luma) by default in IM7. Under what circumstances is gray assumed linear?

The document www.imagemagick.org/script/color-management.php still states that IM "treats any grayscale image as linear rather than non-linear", which may have been true at one time, but not in IM7 (nor in late versions of IM6 I believe). Much of the rest of that html page seems based on this ...

After setting -intensity rec709luma or rec601luma (or even after "-intensity Undefined" or "+intensity", strangely), any later -grayscale rec709luminance or rec601luminance calculates linear gray data as expected, but uses the method from the earlier -intensity setting as the intensity image ...

convert D:\myGrayscaleImage.png -set colorspace RGB -colorspace gray D:\myNewGrayscaleImage.png It's not clear to me why you are including -set colorspace RGB, which is normally used when you need to change an incorrect colorspace designation on an image. If your image is nonlinear (sRGB as most ...

JPEG is color blind. Converting to a non-linear colorspace could be an unexpected transformation for our users whom might expect their linear image to remain linear when they write to a JPEG image. We instead take the raw pixel values and just pass them to the JPEG compressor. In practice and ...

Thanks for your timely response. we assume a nonlinear colorspace unless the colorspace is RGB, XYZ, or xyY. For grayscale we assume linear if the intensity option is Rec601Luminance or Rec709Luminance. Exactly, so when a Gray image has intensity attribute Rec601Luminance or Rec709Luminance ...

For comparison, I'll start by showing a few of the related cases where IM automatically does the necessary conversion to the [non]linearity of the target output format. IM automatically (and correctly) converts linear RGB images to nonlinear when writing to a nonlinear sRGB format like JPEG: magick ...

I'm thinking maybe i should post the docu proposal as a new topic rather than it being buried here in the middle of page 3. If so, should it be here in bugs or perhaps in Developers?

I welcome Dabrosny's work on this. I can't check the proposed documentation as I don't have a recent version of IM (and won't in the near future). I don't know the answers to Dabrosny's questions (a) to (n). Thanks. Those q's were just meant to describe the motivation for my proposed documentation ...

But you said -intensity is unrelated to -grayscale. I didn't say they were unrelated, but I merely said "The behavior of -grayscale has no effect on the behavior of -intensity". In other words "-intensity" does what it does, whether or not "-grayscale" even exists or works correctly. Nevertheless ...

Why would documentation change anything related to some potential bug report? Because a bug is when the software does not behave as intended, and without documentation we don't know what is intended. Until there is agreement on what the intensity image attribute (on a Gray image) does at all, I can ...

(I haven't yet tried to change the documentation for the -grayscale operation because its behavior has an inconsistency that I'll probably submit as a bug report later, rather than merely documenting its current behavior.) Your issue was with -grayscale. But they both are intertwined internal to IM ...