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Author Topic: ProPhotoRGB  (Read 23186 times)
Ray
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« Reply #40 on: August 05, 2005, 02:51:56 AM »
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But seriously, just how many discrete colors are there in the average 24 bit 33MB 1Ds image? Maybe not 30,000, although I bet some images would have no more than that. 100,000 perhaps? Certainly less than 1 million.
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Mark D Segal
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« Reply #41 on: August 09, 2005, 11:49:08 AM »
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Andrew, fine. But what is the relevance of this information to the issue of whether there is downside risk (in terms of visible degradation of print quality) when using ProPhoto rather than ARGB98 as one's default colour space?
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Mark D Segal (formerly MarkDS)
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« Reply #42 on: August 10, 2005, 10:27:46 AM »
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When you convert (one step), that’s EXACTLY what you get.
Andrew, the softproofing you describe in your last post above is what I have been doing but the phrase I quoted confuses me. I have the softproof set-up the way you say, and to activate it I click "CTRL Y" (Windows XP) which I understand doesn't change anything in the image file - it "simply" renders a monitor image simulating what the printed output will look like - and it does so pretty well. When I click CTRL Y again the simulation disappears. Is this what you mean in the above quote from your post, or do you mean that once I click "PRINT" Photoshop remaps the file data to the output profile for printing (but doesn't retain the remapped data thereafter) or do you mean something else?
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Mark D Segal (formerly MarkDS)
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Ray
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« Reply #43 on: August 10, 2005, 07:43:39 PM »
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There are two options for viewing out of gamut colors under the View menu. One is to setup a soft proof using the output profile, rendering intent and options like Simulate paper/ink. This IS the way to be evaluating the soft proof/out of gamut colors.

The second, older and quite useless way is to pick “Gamut Warning” which places a gray (by default) mask over out of gamut colors based on what you’ve set in Proof Setup. The idea is to desaturate those areas so they fall into output gamut. This is a old, useless, time consuming and not very accurate way to be handling this process.
Well, you guys have got me completely confused. I see only one way of knowing which colors are out of gamut and that's by ticking the gamut warning under 'proof colors' which places a gray mask over the saturated colors.

Perhaps there's something very obvious that has escaped me, but if I don't see the gray mask, how do I know the colors might be too saturated for the paper/printer?

I understand the point that Adobe's gamut warning might be hoplessly inaccurate and that it's better to let the rendering intent (perceptual or whatever) remap the colors so one can be sure one is getting the maximum saturation of a particular color on the paper, if that was the idea when editing, ie. maximum impact of that yellow flower without losing detail.

But 'not knowing' that the colors are going to be remapped, that some of the hues are going to be changed in subtle ways and possibly some of the shadows blocked up because of dark, out-of-gamut shades, seems to me less than ideal.

What's the more precise alternative to the gamut warning, Andrew? This is not clear in your above statements.
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digitaldog
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« Reply #44 on: August 14, 2005, 09:40:11 AM »
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We’re in agreement. On page 35 of my book:

The saturation rendering intent was at one time recommended for solid graphics like logos or pie charts (sometimes referred to as business graphics) and the gamut mapping is weighted to produce the most vivid saturated colors (hence the name). For this reason, using this intent on images can produce less than desirable results. However, depending on the profile and how it was built, the saturation intent might be fine for some images so don’t dismiss it outright. In most cases, this intent really is going to be best used for files that don’t contain images and for use on business graphics and similar types of imagery.  Like the perceptual rendering intent, there are no specifications for how this intent should be applied, so various profiles from different manufacturers will produce differing results.
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Andrew Rodney
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« Reply #45 on: August 17, 2005, 08:51:03 AM »
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No, that's not the right figure.

2 to the power of 48 is:

281 474 976 710 656
Okay! So it's 281 British billion. That's an even more unrealistic figure. You'd need a Supercomputer and a lot more than Photoshop to handle an image containing all those colors. Does a few billion make any difference in such circumstances, apart from slowing everything to a crawl.
NO image could contain that color. Even if it could, we could see a tiny fraction of those colors (we can’t even see anything close to 16 million color simultaneously). This is all math being used to define a possible but unfortunately impossible human experience. Don’t forget, there’s math that says a bumblebee can’t fly.
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Andrew Rodney
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jani
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« Reply #46 on: August 17, 2005, 09:26:40 AM »
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NO image could contain that color. Even if it could, we could see a tiny fraction of those colors (we can’t even see anything close to 16 million color simultaneously). This is all math being used to define a possible but unfortunately impossible human experience.
An image can contain an infinite number of colors (unless you mean to imply that wavelengths of light exist only in a finite, discrete set), but there are limits to what you can capture.

A pixel can only have one RGB value, and the limit of discrete colors in a pixel-based image therefore depends on the number of uniquely colored pixels in it.

To create an image with 281 474 976 710 656 different colors, you only need to create an image with as many pixels, all with different RGB values.

As for Ray's point about supercomputers and whatnot, the fact that we deal with RGB values per pixel indicates that an 48-bit color image's uncompressed size in memory should be:

48 bits * width in pixels * height in pixels

E.g., a 300 000 * 300 000 pixel image (Photoshop CS's maximum, right?) could be:

48 * 300 000 * 300 000 = 4 320 000 000 000 bits = 540 000 000 000 bytes.

Plus overhead.

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Don’t forget, there’s math that says a bumblebee can’t fly.
Really? Please show and tell. As far as I know, this is only a popular urban legend, of the kind that is told to ridicule engineers/mathematicians/scientists. There is another, apocryphal story explaining how this misunderstanding could have spread, and it's told here:

http://www.ilr.tu-berlin.de/WKA/technik/bumblebee.html
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Jan
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« Reply #47 on: August 03, 2005, 07:10:19 PM »
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The only con to ProPhoto is a slightly greater chance of posterization or banding if editing in 8-bit mode. But if you use 16-bit mode (which you should be doing anyway) this is irrelevant and there is no real downside to ProPhoto.
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digitaldog
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« Reply #48 on: August 04, 2005, 08:16:59 AM »
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Maybe he’s photographing canaries and doesn’t mind huge steps in color tone. All you get is 256 tones REGARDLESS of the color space (sRGB, Adobe1998, or ProPhoto). Stretch 256 tones over a large color gamut and banding could be troublesome.
No, I bring the RAW into Photoshop in high bit (more than 8-bits per color). Photoshop calls all files with more than 8-bits per color “16-bit” (it’s actually 15 bits).
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Andrew Rodney
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lester_wareham
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« Reply #49 on: August 04, 2005, 04:09:45 PM »
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"So, unless you are shooting canaries (or more realistically, very unusually intense sunsets -..."
The tones I have had clipped in AdobeRGB were yellows and blues in flowers. One way around this is to reduce saturation or 'brightness' in ACR, not that nice in terms of over all image.

However some clipping might be acceptable, and as pointed out these will get clipped at output or desaturated by perceptual rendering it seems.
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Hermie
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« Reply #50 on: August 05, 2005, 04:38:35 PM »
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Why should any one edit using colors they can not print, today?
It's the "round peg in a square hole" metaphor that Andrew posted or as Bruce wrote "It's the trade-off you make when you want to create an RGB matrix space that contains all the realizable colors from your printer".

We edit using colors that we cannot print all the time when we work in aRGB or even sRGB.

Andrew, do you have any thoughts on this one:

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By the way, does anyone of you use

- basICColor display profiles (gamut-compressed profiles, which reasonably simulate colors outside the monitor gamut) or
- Photoshop's "Desaturate Monitor Colors" control

in relation to ProPhoto workflow?

Herman
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digitaldog
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« Reply #51 on: August 06, 2005, 06:12:25 PM »
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Yes. As I wrote, R255 in sRGB and Adobe RGB (1998) share the same numbers. But R255 in Adobe RGB is much more saturated. If you look at the gamut plot of both in the CIE chromaticity diagram you’re seeing the two within the context of all human vision. The larger plot holds more visible colors.
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Andrew Rodney
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Ray
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« Reply #52 on: August 06, 2005, 10:22:34 PM »
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As far as I have been able to parse it, this whole discussion about whether or not it is useful to work in ProPhoto color space so far boils down to two propositions: (a) if Prophoto includes - but ARGB98 excludes - values that current and future generations of printers can reproduce, we should retain those values because they will improve printed image quality; ( as long as we work with 16 bit data, there is very little risk that Photoshop's shakedown of out of (printer) gamut colors will produce any noticeable banding.
Mark,
Understood! But Paul's point about the values being retained in any case if you are in the habit of keeping your RAW files (and who isn't?), has a certain validity. The argument, already made earlier, that you might not want to rework an image because you've spent a lot of time editing it, also has a certain validity, but it's not clear to me just how valid this point is.

If your monitor cannot even display the full gamut of ARGB, then how valid is any current editing in respect of an even wider gamut that you might be able to use in say 10 years' time. You are going to want to re-edit that image using a future monitor that can display the full gamut of ProPhoto.

If I'm in a situation where I'm revisiting 10 year old images with a view to reprinting them using a monitor that can display the full gamut of ProPhoto and a printer with the same capability, then I think it might be better to go to the original RAW image and reconvert it using the latest version of ACR which will almost certainly be a better converter with more options and a better capability of extracting detail and color.

So for me, the more immediate concern is, what colors and shades can we print from ProPhoto that we cannot print from ARGB, on the latest printers such as the Epson 4800, and on what papers?

Not that I'm arguing against the use of ProPhoto. If there's no downside of any practical significance, then one might as well convert into ProPhoto. It's at least another copy of the image that would certainly be more useful than an ARGB copy for future purposes if you were to lose the original RAW.

No point in needlessly depriving oneself of possibilities.  Cheesy
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Mark D Segal
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« Reply #53 on: August 11, 2005, 09:00:46 AM »
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Thanks Andrew - much better - you've provided some substantive food for thought about the conditions under which these comparisons should be made for them to be reliable. That is important. Only Ray knows how he did his comparisons, so up to him to clarify.
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Mark D Segal (formerly MarkDS)
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Ray
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« Reply #54 on: August 14, 2005, 09:56:43 AM »
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Some time ago I visited a friend I hadn't seen for some time, a French lady who has taken up painting (perhaps in preparation for her retirement). She lives in a big house with a huge living room that is adorned with very precise copies of the French imressionists, as well as Van Gogh works. (It's quite legal to copy art works as long as you don't pass them off as originals.)

Of course I photographed them all with my D60 and promised to send her prints, but I've been putting off the job. I wanted to do full justice to those rich, impressionistic colors.

I've discovered 'saturation' rendering intent and the colors are fabulous on my Epson 7600. Van Gogh would be proud of them  Cheesy .
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Ray
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« Reply #55 on: August 17, 2005, 03:01:04 AM »
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A bigger space DOES mean more colors.
A color space doesn't have a bit depth! It's the image that has a bit depth. So the following statement is true: An image with a given bit depth has the same number of tones, regardless of the color space it's in.
This is what I'm having trouble following. As I see it a bigger space does not mean more colours. It means the possibility of colors with greater saturation or intensity. The actual possible number of colors is determined by the bit depth. To put it another way, a 24 bit apple can be cut up into 16.7 million pieces, each piece representing a color. A 48 bit apple can be cut up into 68 billion pieces (is that the right figure?), each piece representing a color. The apple is the same in both cases.

An image with a given bit depth does not necessarily have the same number of tones. Any 48 bit image can have fewer tones than a 24 bit image. It depends on the image.

A 48 bit image has the possibility of a much greater number of tones than a 24 bit image. As I mentioned before, it's a theoretical maximum that could only be realised in a huge image; far bigger than Photoshop could handle.
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Mark D Segal
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« Reply #56 on: August 17, 2005, 01:35:54 PM »
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Herman, yes that is technically correct as far as the camera and the RAW file go, but once converted to an RGB image with the interpolation that occurs I believe it has the numerical effect of representing the much larger number of potential HSB values, eventhough it doesn't start that way.
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Mark D Segal (formerly MarkDS)
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paulbk
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« Reply #57 on: August 03, 2005, 08:49:24 PM »
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re: ProPhoto as working space
Apparently there’s two schools of thought on this. Some say it’s better to use a ‘working space’ that closely matches that of your output media (paper). That way there’s less compression during the conversion from working space to print space.

Imagine three concentric circles, Small, Medium, Large.
Let:
1) Small represent the color space of your printer/paper combination.
2) Medium represent the MatchColor RGB color space which covers the Small but not excessive margin.
3) Large represent the ProPhoto color space which covers the Small and the Medium but lots of excess margin.

Now if there are 256 shades from the center of any circle to its circumference. Then clearly the Large color space requires more compression to squeeze into the Smaller color space during print rendering. (assume Relative rendering intent) I don't see what's being gained. In fact, if this logic sound (?), you are actually losing tonality. No?

Or, are “we” saying, do the RAW convert in ProPhoto then convert to MatchColor RGB in Photoshop?
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paul b. kramarchyk
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Ray
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« Reply #58 on: August 04, 2005, 10:39:07 PM »
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So, unless you are shooting canaries (or more realistically, very unusually intense sunsets - see Figure 6), almost all of the tones you can print or are likely to be able to print in the short to mid term future, are nicely contained within AdobeRGB.
This is an interesting discussion. I don't claim to have any great understanding of color management and color theory. I have Photoshop books on my shelf, and many other books on diverse topics, which I have not found the time to wade through; just peeked at occasionally.

But there are a few apparent facts that leave an impression on my simple mind.

(1) 255,255,0 prints out yellower on premium lustre on my 7600 from the ProPhoto colour space than it does from ARGB.

(2) RGB yellow on the swatches pallette (in PS CS )translates to different combinations of yellow and cyan on the info palette, according to the chosen working space; namely, sRGB 87%Y+8% C; Colormatch 80%Y+6%C; ARGB 97%Y+9%C; ProPhoto 100%Y.

These values are all out-of-gamut, indicated by the exclamation mark, but in relation to the SWOP standard, I assume. But there's a question here that perhaps someone would like to answer.

Now to the canary situation that Paul refers to. The implication is, if your photo does not have exceptionally bright and saturated yellows, then using ProPhoto as your working space will serve no purpose and might even have disadvantages.

Now that certainly makes sense, but have we missed something? Your image might not have (indeed is unlikely to have) a pure RGB yellow. But there might well be other shades, some quite dark even, that require that 100% yellow, in conjunction with the other primaries, that only ProPhoto can deliver.

Another point I'd like to make is in relation to banding in 8 bit. There seems to be some concept that because Prophoto stretches the gamut, the 0-255 values will be wider spaced and we might see gaps.

In defense of this possible downside (not a particularly good defense I might add because I can't now locate the source of the information) my understanding is a typical image in 24 bit color does not contain anywhere near the potential 16.7 million shades of colour. We should remember that this is the pallette to choose from. Any image that was required to represent all 16.7M colors would be of necessity an image in excess of 50MB without any extrapolation. Futhermore, every pixel would have to be unique; ie. a different value of RGB.

In practice, a typical 24 bit image (from vague memory) contains just a few thousand discrete colors. I'm reluctant to put a figure on it, but I think we're talking about 30,000, plus or minus. (Or is that the number of genes in the human genome  Cheesy ).
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Hermie
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« Reply #59 on: August 04, 2005, 04:09:24 AM »
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Why? The argument for working in 16 bit applies equally to sRGB and ProPhoto.

Does not apply *equally*. In the case of ProPhoto it's not only the extra headroom argument that applies to 16-bit edits. There's an additional argument, because ProPhoto is such a large space you just need more data points to avoid posterization/banding when converting to smaller spaces like sRGB or a printer profile.

Herman
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