Legacy ImageMagick Discussions Archive

I understand that JPG file (sRGB) are corrected for gamma (2.2 if I am not wrong).
How do I "de-gamma" it? i.e. remove the gamma correction, using command line option?

try converting it to a linear color colorspace, RGB or use -gamma 1/2.2 = 0.454545

convert image.jpg -colorspace RGB newimage.jpg

convert image.jpg -gamma 0.454545 newimage.jpg

I tried "convert image.jpg -gamma 0.454545 newimage.jpg" but it gave me the following error:
"Insufficient memory (case 4) newimage.jpg @ error/jpeg.c/JPEGErrorHandler/296"

Then I tried this "convert -limit memory 1 -limit map 1 image.jpg -gamma 0.454545 newimage.jpg" but it gave me the following error:
"unable to extend cache 'image.jpg': No space left on device @ error/cache.c/OpenPixelCache/4139"
"Application transferred too few scanlines image.jpg @ warning/jpeg.c/JPEGErrorHandler/293"
...

What else can I do?

I am using WinXP command line option. The file size is 50MB

Sounds to me like your computer has no disk space available!

oh yes "convert -limit memory 1 -limit map 1 image.jpg -gamma 0.454545 newimage.jpg" works after I freed some harddisk space.

However "convert image.jpg -gamma 0.454545 newimage.jpg" still fails. Must I use the "-limit memory 1 -limit map 1" all the time? What is this option doing actually?

Forcing the use of temporary disk for image data cache, rather than memory, though that switch should be reasonably automatic.

Hi Anthony,
I want the so called "raw" image pixel, ie. with the gamma effect removed.
Are you sure it is "-gamma 0.454545", not "-gamma 2.2"?
I am confused.
Could you please help?
Thanks...

Why not "-colorspace RGB". It converts your image to linear RGB for further operations.

sRGB is very similar to gamma 2.2, but not exactly the same. Not sure about AdobeRGB (some DC produces AdobeRGB instead of sRGB).