Re: evaluating identical media in incorrect lighting conditions
Re: evaluating identical media in incorrect lighting conditions
- Subject: Re: evaluating identical media in incorrect lighting conditions
- From: Steve Upton <email@hidden>
- Date: Tue, 27 Jan 2004 13:00:20 -0800
At 1:01 PM -0500 1/27/04, John MacDonald wrote:
>
I am often asked to evaluate color under incorrect lighting conditions. Most of the time, I can convince whoever is asking that this is a bad idea.
>
>
Sometimes, however, I am evaluating two images printed on an identical medium; for example, a "before and after" demonstration of a color correction on the same photographic paper, or two identical prints at two different sizes.
>
>
I have always argued that these should still be evaluated under balanced lighting conditions, but invariably someone says something like "but if the color is off, it'll be off in the same way". I don't believe this and my experience shows otherwise, but I have a difficult time explaining why.
For problem #1, lighting - if they are on the same photo paper then the differences in lighting will mostly go to expose different image characteristics more. So differences in the blue regions of an image will be more noticeable under daylight, etc. If they are on different ink/paper types then metamerism is the biggest factor. The simplest explanation I have found is to first describe that typical ICC systems calculate all colors to be viewed under D50 lighting. When the lighting differs from D50 (daylight is my favorite example with much more blue light) then it can play a big role...
For problem #2 image size - this is a bigger deal than many people realize. The ICC standard is based on 2-degree, D50 Lab. Your thumbnail held out at the end of your arm is a rough example of an image entering your eye at 2 degrees. Bring your thumb (or an image) closer to your eye and it paints a considerably larger image on your retina. This images outside of your fovea and changes the mix of rods vs cones doing the sensing. This affects your color perception enough that another standard observer with a 10-degree angle-of-entry was created. So, small prints look different than big ones. I have found that small prints don't match when larger prints (or portions of the larger print at the same scale) match.
Hope this helps.
Regards,
Steve
________________________________________________________________________
o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX
o email@hidden 206.985.6837
o ColorGear ColorThink ColorValet ColorSmarts ProfileCentral
________________________________________________________________________
--
_______________________________________________
colorsync-users mailing list | email@hidden
Help/Unsubscribe/Archives:
http://www.lists.apple.com/mailman/listinfo/colorsync-users
Do not post admin requests to the list. They will be ignored.