Legacy ImageMagick Discussions Archive

Whereas a non-Gray image is treated by IM as having nonlinear or linear values based solely on its colorspace irrespective of gamma I am not sure this is true. I think IM will make sure a linear image has gamma=1. ... But I will defer to the IM developers to correct my statements. A -colorspace RGB...

In order to understand what -intensity does and how it replaces the old nonlinear and linear grayscale colorspaces, I did some experimentation and this "-intensity" documentation entry is based on what I believe is the actual behavior of IM 7 (at least in 7.0.6 x64 q16 HDRI). See my preced...

Originally, I just wanted grayscale images (linear and nonlinear) to work the same as RGB and sRGB, but I discovered that grayscale images are now far more complex than color images, in the way that their linearity is not determined by their colorspace, and the -intensity affects not only how a gray...

In IM 6.9.9.9 Q16 Mac OSX and -grayscale Rec709luminance, I get (same for IM 7.0.6.9 Q16 HDRI using magick) convert rose: -grayscale Rec709luminance -write rosegray.miff -separate rosegrayRGBseparated.miff ... So they are identical and after -separate, both are gamma=1 The grayscale image (result o...

My point is that most external format do not keep track of linear vs non-linear and many do not even store the gamma. I simply wanted to show that internally, IM keeps track of that. Absolutely, and IM is very good at keeping track of that metadata. I just want to make sure we know what the expecte...

So l2 will display as linear, but l3 will display as non-linear. I'm not sure precisely how you're defining "display as linear" (gamma=1? colorspace=RGB? intensity=rec*luminance? behavior of im display app?), but what I'm most interested in is how an image "displays" after IM ha...

I would be able to modify the documentation. Feel free to write a draft. Okay, will do. But I am not sure I understand. The only way it "tags" the image as linear if via the gamma for external formats. With MIFF, you can look at the header to see if it linear or not, as I recall. Okay, I ...

Fred, what would you think about the idea of something being added to the current documentation of "-intensity" just to at least state the fact that it tags the resulting Gray image as linear or nonlinear (so that IM knows how to correctly convert it back to a non-Gray colorspace)? I'd eve...

I note that "-grayscale rec709luminance" and the other three all leave the gamma unchanged at 0.454545. In my opinion, the conversions to luma should set gamma to 1.0. But they do set the intensity settings. Perhaps IM is moving away from the use of gamma, towards the use of intensity set...

A linear RGB image having R=G=B literally represents the same image as an sGray I do not agree with that. My mistake, I should have said that a linear RGB image having R=G=B literally represents the same image as an linear grayscale image with linear luminance ("Y" of XYZ if you like) hav...

Storing the same data, or metadata, in multiple places isn't a good idea. What happens when the multiple values disagree with each other? Pixel values may represent linear data, or not. This information is currently represented by metadata (a) colorspace, (b) gamma and (c) profile. Fairly recently ...

There is only one colorspace in IM for gray. But you can achieve many different forms of grayscale. I thought that was the real issue. To get linear gray and keep it linear when doing -separate and -combine. I showed that worked for me. The issue is to document the criteria by which a Gray image (c...

Although in fact it seems clear from the formulas in the documentation that Lightness and Brightness always use the nonlinear (sRGB) values ... The documentation is misleading (or simply wrong). Okay, the documentation should be updated to move Lightness and Brightness into the "mathematical&q...

But you can use -grayscale to convert to linear or non-linear grayscale using rec709luminance or rec709luma as well as rmse and average. So there are many different forms of grayscale. Not just one from -colorspace RGB. Just because a different formula (different coefficients) might have been used ...

Is the "-intensity" setting a good way of flagging that data is linear? No, I don't think so. For one thing, when changing colorspaces, the "-intensity" setting is only used when the colorspace was Gray, Rec601Luma or Rec709Luma. I agree that -intensity isn't a good way (in fact...