creating web images that have the same brightness on Windows and Mac monitors

[LRK@adobeforums.com]

Whoops, cross-posted.

Still...

One member there said the following:

You do not have to stick with Mac gamma of 1.8. That is really a relic of
the past. Most people calibrate their monitors to a gamma of 2.2 and 6500k.

Now that I'm accustomed to 2.2 and 6500, I find that going back, the brightness now bothers me... something that at one time I preferred. Interesting. I still wish Apple would fix those ugly dark drop shadows on the desktop though.

I've also seen an improvement in that my monitor now matches my Xerox 790 printouts better... that is when it prints, ugh!

[Ramón_G_Castañeda@adobeforums.com]

Thanks for that link, Ronald. I'm going to have to use gamma 2.2 from now on. I'll test it first, though, to see how my existing images look.

[Ronald_Lanham@adobeforums.com]

Linda,

What am I missing here?

At 6500K instead of the native white point don't your colors shift dramatically?

[LRK@adobeforums.com]

Ron: Yes, they do. And when I first used 6500K I hated it. Now that I'm used to it, I think it's probably better.

[Tim_Lookingbill@adobeforums.com]

If you refer back to Bruce Fraser's quote, the central issue isn't the gamma number. It's whatever gamma it takes to allow the viewer to see all gray levels evenly distributed in a grayramp between 0,0,0rgb to 255,255, 255rgb after finding the darkest black level setting your monitor can display that can't be darker than with the monitor turned off.

You may notice this black level and even gray distribution viewing standard may not be the same between monitor brands and especially between LCD's and CRT's.

Whatever gamma chosen after establishing black point that retains this environment is the gamma number to settle on. Gamma 2.2 is a "standard" that comes closest to retaining this environment on most monitors and reduces file degradation when converting from the wider color managed space of AdobeRGB to the standardized so to speak uncalibrated PC monitor space of the web's sRGB which have the same gamma.

If you can see all 21 levels of a 21step grayramp RGB target with the monitor calibrated to 2.2 gamma with the blackest black the monitor can generate, stay with it.

[LRK@adobeforums.com]

Good point... and well said Tim... funny I'd forgotten about the ramp... which was the main issue.

[Bruce_Fraser@adobeforums.com]

In almost all monitors being sold today, the only way to adjust the gamma of the display system is by tweaking the 8-bit/channel lookup table in the video card, and when you do that, you lose levels, just as you do when you apply a gamma edit to an 8-bit image.

The bigger the tweak, the more levels you lose, so the further away you take the display from its native gamma, the more likely you are to see banding in gradients. The gamma 2.2 recommendation stems from the fact that the unadjusted behavior of most CRTs connected to Macs comes in pretty close to gamma 2.2. On those systems that allow it, I prefer to leave the gamma unadjusted, and simply profile the display at native gamma.

[yassy@adobeforums.com]

I check "Embed Color Profile" checkbox when i save the web file in PS.

[Tim_Lookingbill@adobeforums.com]

Bruce,

I just read the Charles Poynton article on what Quickdraw does to gamma. Has that been worked out by Apple, now?

I never considered that Quickdraw had so much influence in respect to gamma.

I can't use 2.2 gamma because it causes the gray levels in the grayramp to go to black at level 13. 1.8 flattens the middle. So I use a 2.4 based perceptual curve in SuperCal. I can now pass your PS black level test only I do have shifts in cast at those levels.

[Bruce_Fraser@adobeforums.com]

Quickdraw went away in OS X, being replaced by Quartz. But Charles' info on Quickdraw is very old indeed—it started being less than definitive back in OS7, when the "uncorrected gamma" option was introduced—it turned off Quickdraw's gamma correction.

If gamma 2.2 turns your grays black at level 13, either the gamma is being miscalculated or, more likely, the black point is being set incorrectly (which is almost guaranteed with visual calibrators like SuperCal), possibly because the white luminance is also being mis-estimated.

[Tim_Lookingbill@adobeforums.com]

I set black point visually with the overscan method which makes the screen seem even darker. I can adjust the brightness button and level 13 will show up, but then I'm not getting the blackest black the display can produce.

Even if I lighten the black point, 2.2 produces an unevenly distributed grayramp much like 1.8. There is an abrupt shadow increase from level 13 on up to 128 and then it smooths out.

The perceptual curve elliminates this. I get a very smooth grayramp.

Thanks for the input, Bruce.

[jessekelvin]

I haven't installed CS4 yet, but in CS3 you can not run a custom action in the same process as creating a gallery using File->Automate->Web Photo Gallery.