Bad Colors with colorspace and gamma options

[jake9wi]

On windows seven x64 using version 7.0.8-3 the image returns with good colors but with version 7.0.8-38 colors are distorted.

link to images: https://www.dropbox.com/sh/lzbule9mcn78 ... vyIKa?dl=0

Code: Select all

magick.exe original_fdc_o_ea.png ^
-colorspace CIELAB -intent Relative ^
-colorspace sRGB -intent Relative ^
-gamma 0.8 -type Truecolor  test_708-38_fdc_o_ea.PNG"

[dlemstra]

Can you reproduce this issue with ImageMagick 7.0.8-39 that has just been released?

[fmw42]

It does not reproduce the original colors for me in 7.0.8.39 Q16 Mac OSX. But does with IM 6.9.10.39 Q16.

[jake9wi]

Yes, 7.0.8-39 still produces the error.

[magick]

What do you get for these commands:

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$ compare -metric rmse  test_708-38_fdc_o_ea.PNG  original_fdc_o_ea.png null:
1567.21 (0.023914)

$ compare -metric rmse test_708-03_fdc_o_ea.PNG  original_fdc_o_ea.png x:
1567.21 (0.023914) 

$ compare -metric rmse  test_708-38_fdc_o_ea.PNG  test_708-03_fdc_o_ea.PNG null:
0.606276 (9.25117e-06)

Which suggests ImageMagick 7.0.8-39 is producing nearly the same exact results as 7.0.8-3. If you get different results, the problem may be a Windows/Mac issue.

[jake9wi]

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A:\z_zip\imagemagick\708-39>compare.exe -metric rmse test_708-38_fdc_o_ea.PNG original_fdc_o_ea.png null:
13129.2 (0.200338)

A:\z_zip\imagemagick\708-39>compare.exe -metric rmse test_708-03_fdc_o_ea.PNG original_fdc_o_ea.png null:
1567.21 (0.023914)

A:\z_zip\imagemagick\708-39>compare.exe -metric rmse test_708-38_fdc_o_ea.PNG test_708-03_fdc_o_ea.PNG null:
13035.3 (0.198906)

[snibgo]

magick.exe original_fdc_o_ea.png ^
-colorspace CIELAB -intent Relative ^
-colorspace sRGB -intent Relative ^
-gamma 0.8 -type Truecolor test_708-38_fdc_o_ea.PNG"

I suggest you simplify the command. What is the simplest that shows the problem?

You are not using "-profile", so "-intent" should do nothing.

If the input is sRGB, then "-colorspace CIELAB -colorspace sRGB" should do nothing.

"-type Truecolor" should not make a significant difference.

"-gamma 0.8" will make a difference, but should be the same in each version. Try with "-gamma 1.0", which should not change the image.

[jake9wi]

The unsimplified command i am using is this:

Code: Select all

magick.exe ..\fdc_o_ea.png ^
-colorspace CIELAB -intent Relative ^
-filter hermite -distort resize "1000x744!" ^
-colorspace sRGB -intent Relative ^
-gamma 0.8 -quality 00 -type TrueColor fdc_o_ea.PNG

Dropping 'truecolor' and 'intent Relative ' still produces the error:

Code: Select all

magick.exe original_fdc_o_ea.png ^
-colorspace CIELAB ^
-colorspace sRGB ^
-gamma 0.8 test_708-38_fdc_o_ea.PNG"

If I set gamma to one or drop '-colorspace CIELAB' the error is not produced.

[snibgo]

...or drop '-colorspace CIELAB' the error is not produced.

Good. That suggests that "-colorspace CIELAB" is changing the gamma setting, but "-colorspace sRGB" isn't changing it back. This should help the developers find the bug.

Meanwhile, as a workaround, I suggest you don't use "-gamma 0.8". Instead, use "-evaluate Pow 1.25". Does that work correctly in both versions?

(Note that 1/0.8 = 1.25.)

[jake9wi]

Using '-evaluate Pow 1.25' still produces the error in ver38 & 39, '-evaluate Pow 1.00' does not produce the error.

In ver3 '-evaluate Pow 1.25' works good like gamma 0.8.

[snibgo]

Okay. This is weird, probably a bug in 7.0.8-38 and -39, possibly restricted to Windows and Mac versions. I'll leave it to the developers.