Legacy ImageMagick Discussions Archive

That is correct. (Except that they are called a and b, not A and B.) And I thought "fully saturated" have different implications in "Lab" and "RGB". Under "Lab", no matter how we manipulate "a" and "b", "L" should not be affected. Even if it is converted to 8-bit RGB and got rounded or truncated ...

I thought A and B control the "hue" and "saturation" only... having no effect on luminance.

Awesome, thanks! By the way, can you give the steps you use to build on MinGW + windows? I was having some issues due to pthread and such (which I ironed out using the pthread for windows port) but I want to check if there is a better / easier way I once worked out a way to compile it under mingw32 ...

Found something strange.... convert.exe -respect-parentheses \ rose: -set colorspace sRGB -colorspace LAB \ -channel R -separate placebo_%d.png convert.exe -respect-parentheses \ rose: -set colorspace sRGB -colorspace LAB \ -channel G -sigmoidal-contrast 9,50% \ -channel B -sigmoidal-contrast 9,50 ...

If it is a problem of "-separate", "b_0.png" should have been fine.

but "b_0.png" is wrong (in the same way) even if I put "RGB", "LUV", "HCL", etc. in place of "sRGB" in the middle.

@henrywho: if you want to increase saturation while leaving the L of Lab unchanged, the obvious way is to do it in Lab space. The a and b channels both record saturation as the distance from 0.5, that is a=b=0.5 (in the range 0 to 1) represents zero saturation. So apply the same "-sigmoidal ...

I am using Win32 Q16 static compile: Version: ImageMagick 6.8.3-5 2013-02-24 Q16 http://www.imagemagick.org Copyright: Copyright (C) 1999-2013 ImageMagick Studio LLC Features: DPC OpenMP convert.exe rose: -set colorspace srgb -colorspace hcl -channel R -gamma 1 +channel -colorspace lab -channel R ...

Actually, I am trying to increase the saturation so "-gamma 1.5" seems more appropriate.... except that I am looking for a way not to touch the pixels with high saturation.... something like "if saturation > threshold then untouch else increase it". Looking for some simpler way other than masks ...

Just tried something like:

convert.exe input.png -set colorspace srgb -colorspace hcl -channel G +sigmoidal-contrast 3.5,49% +channel -colorspace srgb output.png

Not bad.... but I need something asymmetric so as not to de-saturate the high-saturation areas. Do u guys have any idea?

For whoever interested, *.mp4 has posted five interpolation kernels in Doom9:

http://forum.doom9.org/showthread.php?t=166080

try specifying a font like Arial Unicode MS or PMingLiU

Agreed with fmw42.

A sharpened JPEG saved at a lower quality may have similar size as a smoother JPEG saved at a higher quality.... but looking much worse.

Or search in the following order:
1) same directory or specific subdirectory of convert.exe/magick.exe
2) environmental variable (e.g. MAGICK_CONFIGURE_PATH)
3) HKCU
4) HKLM

Must read: http://www.imagemagick.org/Usage/filter/nicolas/

Last week I was resampling some large web banners (with transparency) into small paletted (8bit) icons. I also ended up with flatten-then-resample: convert big_banner_with_alpha.png -set colorspace srgb +repage \ -colorspace lab -background white -flatten \ -define filter:window=Quadratic -define ...