Colour space aware resize in 6.7.1

[Rahulp]

I am attempting to setup a gamma aware resize script as per http://www.imagemagick.org/Usage/resize ... colorspace but the commandline

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convert earth_lights_4800.tif -colorspace sRGB -resize 500 -colorspace RGB  earth_lights_srgb.png

...is producing the same dull output as ...

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convert earth_lights_4800.tif -resize 500 earth_lights_direct.png

I am using ImageMagick 6.7.1-0 2011-11-23 Q16 on OS-X

[Rahulp]

No one has any insight r.e. what might be wrong?

[fmw42]

Search the archives. This has been discussed at length. See for example viewtopic.php?f=2&t=15955&p=71461&hilit ... ize#p71461

Also see http://www.imagemagick.org/Usage/resize ... colorspace

[anthony]

The last link above
http://www.imagemagick.org/Usage/resize ... colorspace
has already been updated with what has changed, BUT so far the main IM Web site is not yet showing that change.

Essentually as of IM v6.7.5-1

• images by default have a colorspace setting of sRGB, instead of RGB
• sRGB actually means sRGB colorspace! as such using -colorspace RGB converts it to linear-RGB

The basic result is that after this version you would use

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  convert earth_lights_4800.tif -colorspace RGB -resize 500 -colorspace sRGB  earth_lights_colorspace.png

Another way to determine if you IM is new enough if to do

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  identify -verbose rose: | grep Colorspace

if the result is

Colorspace: sRGB

then it has been updated

When saving either RGB or sRGB the image data will be saved as is. That is automatic colorspace conversion on write is turned off for either RGB and sRGB colorspaces. I am not however sure if the PNG image format marks the image as being linear or non-linear as few PNG program seem to take notice of it, unless a profile is also added.