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: Wed, 28 Jan 2004 11:14:56 -0800
At 9:32 AM -0500 1/28/04, Mike Syverson wrote:
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>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.
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Steve,
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I was wondering if you could explain this concept further. We do a lot of work with grand format printers and often times deal with a very small proof to compare to. If I have a better understanding of this principle, it will make viewing proofs easier.
Well it all comes down to how big an image it paints on your retina. When an image (or portion) enters your eye across a 2 degree arc, it is pretty much concentrated on your fovea (assuming your are looking straight at it). The fovea contains highest concentration of cone cells in your eye and so, the vast majority of your color vision.
Paint a larger image on your retina and you change the concentration of cones vs rods quite a bit.
Just to settle my(our) curiosity I did some color-shift calculations to see what kind of color differences we might see.
Using the Atkinson 9.18 RGB target printed on an Epson 2200 and read spectrally I converted to 2 deg D50 Lab and to 10 deg D50 Lab. The difference between the files is significant. Most of the color shifts occur in the saturated blues and dark blues. The results are:
dE
Overall: 5.21
Best 90%: 4.25
Worst 10%: 13.79
Worst Patch: 19.4
dE 94 (CMC 2:1 is pretty similar)
Overall: 2.66
Best 90%: 2.13
Worst 10%: 7.32
Worst Patch: 10.5
So there is a significant difference between the two "standard observers" and we can infer, between one observer viewing color samples at different "magnifications".
In the large format world what I would suggest is either printing small portions of your image at the same magnification as the final product - if possible, or perhaps setting up a viewing condition to simulate how large you, the client, etc will view the final results. You could even do print to final comparisons by having the final result at a distance and the proof close by so they look about the same size... lighting that could be tricky though. Good luck, if you need help, let me know.
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
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