Search found 5 matches

by hochgurgler
2011-04-15T02:47:05-07:00
Forum: Developers
Topic: Resizing properly in a world of {default=sRGB}
Replies: 18
Views: 48729

Re: Resizing properly in a world of {default=sRGB}

The razor which determines whether this issue is solved is as follows: We use the test image from Eric Brasseur's page http://www.4p8.com/eric.brasseur/gamma.html : http://www.4p8.com/eric.brasseur/gamma_dalai_lama_gray.jpg Resize this image to 50% linear-dimension without using any special flags. I...
by hochgurgler
2010-04-09T08:21:01-07:00
Forum: Developers
Topic: Resizing properly in a world of {default=sRGB}
Replies: 18
Views: 48729

Re: Resizing properly in a world of {default=sRGB}

Input image (alternating black and white lines) convert lines.png -resize 50%% lines1.png lines1.png: { A largely uniform rectangle of pixels #7F7F7F } convert lines.png -gamma 0.45454 -resize 50%% -gamma 2.2 lines2.png lines2.png: { A largely uniform rectangle of pixels #BABABA } "%IMG%convert lin...
by hochgurgler
2010-04-09T05:41:46-07:00
Forum: Developers
Topic: Resizing properly in a world of {default=sRGB}
Replies: 18
Views: 48729

Re: Resizing properly in a world of {default=sRGB}

A great majority of image processing algorithms assume a linear colorspace for correct results. However, the ImageMagick policy / philosophy is to assume the user knows what they are doing and to not do anything automatically. Its up to the user to use the -colorspace option or profiles to convert ...
by hochgurgler
2010-04-09T03:16:54-07:00
Forum: Developers
Topic: Resizing properly in a world of {default=sRGB}
Replies: 18
Views: 48729

Re: Resizing properly in a world of {default=sRGB}

I thought that was the function of "-set colorspace", ie convert in.png -set colorspace sRGB -resize 50% out.png does the resize assuming the pixels of in.png are sRGB, so it will do (roughly) the "-gamma 0.45" before the resize and "-gamma 2.2" after. Thank-you for replying. OK that does sound log...
by hochgurgler
2010-04-08T02:56:04-07:00
Forum: Developers
Topic: Resizing properly in a world of {default=sRGB}
Replies: 18
Views: 48729

Resizing properly in a world of {default=sRGB}

I've read Eric Brasseur's Gamma article at http://www.4p8.com/eric.brasseur/gamma.html, and I am now miffed with pretty much every graphics tool I have. Eric has pointed out particularly about resizing, but similar problems would apply to any other operation which does algebraic operations on pixel ...