Color Calibration and Your Monitor

[gare]

Hiya, Nitro--

Monitor calibration---just a little of it, not obssesively, y'know--is important for a number of reasons.

First, Windows has a native target gamma of about 2.2-2.5, and the Mac OS uses 1.8. To add to the confusion, Mother Kodak...may she be wiped out by digital photography...writes PhotoCDs to a color lookup table of 0-346 instead of the standard, 8-bit 0-255; fortunately, if you use Auto Levels in PS, PhotoCD images usually snap right back to proper tone balance.

Next, are you going to calibrate for on-screen presentations, or for an inkjet? I've got this stubborn Epson that's hard-wire calibrated for the Mac--my solution is to save a copy of finished work for print, then use PS's Proof View for the Mac--then I deepen the copy using Levels and then goose the Saturation a little. My prints come out fine.

Important trivia: Adobe Gamma panel, that doober that installs into Control Panel in Windows, only affects Adobe applications. I routinely shut it off when I'm doing an image destined for Xara, and BTW if anyone has a better workaround to lend us all, I'm game. Using a default profile in PS of Adobe 1998 color space with 20% desaturation in Advanced options helps, but doesn't totally correct the disparency.

On the Mac, last I used it, colorSync color management is used globally (for all apps), and that's why I believe Adobe doesn't make the Gamma widget for Mac PS.

Adobe Gamma is better than no color management at all (and do NOT run two color management modules), but I guess for the ultra-fussy, there's Barco.

Being an ex-chemical photographer, I used to bracket exposures for color film, but not for chromes, because chrome exposure latitude "forgives" you by about one f-stop. But, geez, digital photography can be pushed by about 3 stops with little degradation and I think that's why color management is so essential. I've seen one or two posts on the "other" forum (TalkGraphics) that look as black as sin, but the poster insists the image looks okey-dokey on their system.

In a nutshell, relativity is Mr. Einstein's business, but doesn't work in practice with digital media. \:/

My Best,

Gare

 

[gare]

Re: Color calibration

(from Welles)

Gare,

Um, Mac native Gamma is 1.8, Windows is generally 2.2 but occasionally may be as high as 2.4-2.6 (TV monitor Gamma). There used to be Adobe Gamma for Mac as well as windows and, generally speaking one is better off letting Photoshop control the color when ink jet printing rather than ColorSync on a Mac if you know how to set up PS color properly and calibrate your monitor. If you aren't using a hardware calibration setup on a Mac the best software profiling app is Berg Design's SuperCal. It does a great job.

http://www.bergdesign.com/supercal/

Good, general info on color calibration is here...

http://www.technologyforall.com/TechForAll/photoshop.html

PS Nice job on that chair, Nitrobutler. :} :} :}

 

[gare]

ooops!

I stand corrected, Welles. I'm dyslectic and got the numbers screwed up. [shhh] Windows has a native gamma of 2.2 which Adobe rounded off to 2.5 in their conversions. Photoshop was first developed on the Macintosh and Adobe implemented the gamma functionality incorrectly. Then when they ported to Windows they fixed the functionality but decided to leave the Macintosh version the way it was.

And PhotoCDs bury the needle; I reposted my wrong comment above--PCDs use a LUT from 0-345, balanced for TVs, not monitors.


The basic problem is that Windows monitors are darker than the Mac, and conversely, Mac images will appear lighter in Windows.

Factling: Although we commonly refer to gamma as the breadth of expression in the midtones, it's technically an interger used to describe the non-linearity of voltage vs. signal output (brightness). Alvy (Pixar) Smith, inventor of the alpha channel, says this:

Gamma is perhaps the most misunderstood concept in computer graphics applications. Part of the reason is that the term is used to mean several different things. In Altamira Composer (Alvy's 1994 channel/alpha-enabled image editor), gamma always means only one thing: Gamma is the term used to describe the nonlinearity of your display monitor.

All computer display monitors (and all TV sets) are nonlinear. This means that if the voltage on their electronics is doubled, their brightness does NOT double as you might expect it to. In fact, it varies as the square of the voltage. If it varied by the square exactly, we would say it had a gamma of 2. But all monitors are slightly different, so the actual gamma of your monitor might be anywhere from 1.4 to 2.6, instead of 2. Very typical gamma numbers are 1.8 for the PC and Mac worlds and 2.2 for the broadcast TV world (and for PCs using TV graphics boards, such as Truevision Targa+), but these should not be taken as gospel. They vary from display to display, even on displays from the same manufacturer. Any gamma other than 1 is "nonlinear".

The other important point is that all computer graphics computations assume linear images. This means simply that half red plus half red gives full red. This is fundamental to the industry.

There are two ways to take care of this mismatch between the nonlinear display and the linear computation: (1) take care of the nonlinearity in the display, or (2) take care of it in the data. Only (1) preserves your data for later use.

Unfortunately, many applications force you to take care of your display nonlinearity by making your image data nonlinear. They do this by assuming the default monitor gamma is 1, or linear. This works, so long as you never use the resulting image for another image computation, and so long as the next display you show the image on (including ink on paper) has the same nonlinearity as your original display. This has "worked" often enough in the past for the mistake to have been tolerated.

Key thought here: if an image looks wrong on your display, change the display and NOT the data.

My Best,

Gare

 

[gare]

...more color calibration

I'm a little twirked off that Adobe is aggresively foisting sRGB as the default color space in PS and Elements, when it's smaller than Adobe RGB (1998)--but printer manufacturers are hard-wiring their inkjets for sRGB, as are scanner makers. And it's mostly because of the brighter-than-bright results; forget the fact that by profiling an image to sRGB, you're losing about 15% of the original color space. Paul Simon was right--Kodachrome makes the whole world look like a sunny day...*sigh*

Anyhow, I read a tech paper that both Adobe RGB and sRGB use a gamma of 2.2.

-g-

 

[gare]

Re: Color calibration

(from Welles)
Quite Right! (About all of the above). I'll use sRGB for screen but Adobe RGB (1998) for all my print work going to an ink jet printer and let Photoshop control the color. Additionally, though I use a Mac primarily, my monitors and most of those professionals whom I know all profile our monitors to a 2.2 gamma. For web, it looks better on the majority of screens.

 

[gare]

Re: Color calibration

Hiya, Welles--

Will Safari correct for the Web/do you use Safari?

Although I'll let the inkjet printer dither down the coors in an Adobe RGB (1998) profiled image, folks here should be aware that newer printers are increasingly using sRGB--so Adobe RGB (1998) profiling of a file might result in duller images. And sRGB slightly overlaps CMY(k)(although these areas are visually trivial for color-sensitive folks). See my crude chart; green is a very visually sensitive color--that's why CIELab's color space is distorted and not a circle or anything. And the CMYK color space really doesn't include black (K, or key plate); black is included for coverage and density; the combination of cyan, magenta, and yellow produces a muddy brown on the printed page without some black.

Shall I move this topic to its own area?

My Best,

Gare

 

[gare]

Re: Color calibration

(from Welles)
Gare,

Shall I move this topic to its own area?

That might make sense. I'm always interested in learning about color/print issues and we're seriously divergent from the monthly challenge. (done -g-)

Will Safari correct for the Web/do you use Safari?

Not that I'm aware of...but I've never given it a thought before and it's not an obvious preference.

Although I'll let the inkjet printer dither down the coors in an Adobe RGB (1998) profiled image, folks here should be aware that newer printers are increasingly using sRGB

Am I correct in thinking that most new ink jet printers are default based on an sRGB profile because that is the profile assigned to most digital camera captures? I know when I print (Epson drivers), I use the settings in Print Preview to establish my image color space and print space and in the print dialog I select 'no color adjustment' so Photoshop is in charge of the color rather than have the Epson driver do a double adjustment.

 

[gare]

Re: Color calibration

(from spECTRe)

A lot of Photographers use ProPhotoRGB, which is bigger than AdobeRGB(1998).
By using proper color management settings, you do not get a dull print, au contraire!

 

[gare]

Re: Color calibration

Welles--

sRGB is being "sold" partially because "consumer" cameras are increasingly saving to sRGB, although jpeg...the most common format to which a camera saves (9:1 compression is typical, and based on my Nikon's results, they're acceptable, although I'll rip to tif if the image warrants it)...jpeg can save profiles, Adobe RGB included, in the file header. Curiously, PS doesn't offer to embed the Adobe RGB (1998) profile in Targa or png, but only tif, psd, and jpeg.

The other reason is that if sRGB profiling is used from capture to PS to printing, some consistency is preserved.

But I think the main attraction is the brilliant prints. Joe Sixpack doesn't care that a good chunk of data's being clipped or remapped when sRGB is used; he only cares that screen brilliance and juiciness show up in his prints.


sPECTRe--

Please don't mistake me; I didn't say that my Adove 1998-profiled images were printing dull, only that sRGB is smaller than Adobe RGB (1998). I'm unfamiliar with ProPhotoRGB, but hey, I'm game. I Googled the term, gleaned that PhotoPro RGB is equivalent to camera RAW, and downloaded the profile from [/color]][url]http://www.dodgecolor.com/downloads.html#colorprofiles[/url]

Let's see!
My Best,

Gare

 

[Welles]

Re: Color calibration

Thanks for the link, Gare. I'm going to give the ProPhotoRGB a try.

 

[sPECtre]

Re: Color calibration

I'll try to gather some info about prophoto RGB. Do not use it in 8 bit mode! It is mostly useful for Photographers shooting in RAW format. Adobe Camera Raw's native format is PPRGB too.

Why use ProPhoto (Uwe Steinmuller) : http://www.outbackphoto.com/color_management/cm_06/essay.html

Understanding ProPhoto (Michael Reichmann) :
http://www.luminous-landscape.com/tutorials/prophoto-rgb.shtml

Beyond Adobe RGB (Matt Hagadorn) :
http://www.naturephotographers.net/articles1203/mh1203-1.html

A PDF about PPRGB by Kodak:
http://www.kodak.com/global/plugins/acrobat/en/service/software/colorFlow/proPhotoRgbPhotoshop.pdf

I think that most major Color Management gurus do use ProPhoto: Ian Lyons, Bruce Fraser, Andrew Rodney, and Martin Evening. That said, the changes made in Pro Photo can be quite drastic, use with caution! The fact that experts use it means two things: they recognize its superiority in certain cases, but they also know how to manipulate files in that color space...

 

[gare]

Re: Color calibration

Funny you should mention Bruce Frasier; he developed Bruce RGB for use in PS a few years back.

I recommend that whether an image is natively captured in 8 or 32-bit, if adjustment is necessary, convert it to 48-bit--the Levels command produces much more smooth results; when you're happy, you then dither down to 8 for print or Web display. I've found less data color space clipping when you work in 32-bit.

My Best,

Gare

 

[sPECtre]

Re: Color calibration

I take that you mean 48bits? usually referred as 16 bit/channel, vs 24 bit aka 8bit/channel.
Some prefer to lay gradients in that bit depth, indeed there is some dithering when going 16>8bit, it is sometimes welcomed.

 

[gare]

Re: Color calibration

Yes, I meant 48-bits; sorry. The dithering back to a "normal" color space I've seen is minor. I've never tried the gradient trick--I will, though.

My Best,

Gare

 

[sPECtre]

Re: Color calibration

No prob , I just wanted to point out the correct terminology for newcomers or beginners.