Luminous Landscape Forum
Raw & Post Processing, Printing => Colour Management => Topic started by: xpatUSA on April 14, 2013, 01:18:53 pm
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I'm really trying to find out what Elements (4 onward?) working file format is. The topic title is to get your attention ;)
I've Googled and Googled until my mind is Boogled!
Now to color pickers. If I open a ProPhoto tagged TIFF sunflower shot in PSE 6, it opens up with pretty yellows on-screen. But Elements color picker shows RGB and HSB numbers that are pretty unsaturated. On the other hand, a simple screen color picker shows the "right" values. If I remove the profile, the screen obligingly changes to an unsaturated appearance but the color picker values do not change.
[as PaulM explains so well below, it's not really an anomaly, but I'm still confused about Adobe's working area]
Am I right in thinking that Elements brings the file data into it's working file for editing (not space) unchanged (until I do something)? I recall reading that the data used for editing is in a ROMM space but can't find the reference, duh.
Now, if I convert the file to sRGB (without removing the ProPhoto file first) the on-screen colors do not change but PSE's color picker numbers do.
Am I right in thinking that Elements has changed it's working file to match an sRGB profile?
OT, but I've been trying to the profile that PSE6 embeds in sRGB images. Anybody know where it is in Windows XP (or is it embedded in the PSE application code?).
Thanks,
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Hey Ted—
The numbers you are describing make sense to me. I don't know much about PS Elements, but from a photoshop and colorimetry point of view it sounds like everything is working as it should.
Here's what's going on:
RGB and HSB numbers by themselves aren't enough to make any judgment about color or saturation. They are both device-dependent—you need to view those numbers as coordinates within a particular space. Without the space you can't make any generalization about a RGB or HSB triplet being 'pretty unsaturated'.
In your example you have an image that is in ProPhoto RGB—a huge space capable of colors so saturated they don't really exist. You also have RGB numbers that you are getting from your monitor via the screen color picker. The screen color picker should be showing you RGB values relative to your monitors space—a much smaller space that can't come close to the max saturation of ProPhotoRGB.
So if the screen color picker is showing you an RGB value of [255, 255, 0] that's going to be the most saturated yellow available in the screen's color space (Since I don't have your monitor profile, I'm going to assume your monitor acts like sRGB). It represents 100% saturation—the most saturated color your monitor can display. But the ProPhoto space can contain much more saturated yellows. In the Prophoto space this yellow might only represent 67% of the possible saturation. To get this same yellow in ProPhoto you would only need the RGB values [234, 251, 84]. It's the same color appearance, but it's well inside the boundary of the ProPhoto space.
If you only look at the numbers you might be led to believe that RGB [234, 251, 84] is less saturated than RGB [255, 255, 0], but once you interpret the numbers within the space you can see the ProPhotoRGB[234, 251, 84] and sRGB[255, 255, 0] represent the same color.
With this in mind everything else makes sense. Say you have an ProPhotoRGB file with that yellow value of [234, 251, 84]. To display it the computer looks at the numbers, converts them to your screen's profile space [255, 255, 0] (in our example) and sends them off. If you strip the profile, the system no longer knows how to interpret [234, 251, 84]—so it just sends the numbers off to the screen resulting in a much less saturated yellow. Because ScreenRGB[234, 251, 84] is less saturated than ScreenRGB[255, 255, 0].
This is also why the numbers change when you convert to sRGB—the numbers change in order to keep the appearance the same.
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Thank you Mark,
You've confirmed what I thought as to the various appearances on the monitor.
So, in Photoshop or possibly LR or even Elements is the image file data itself i.e. the RGB numbers brought unchanged into Adobe's working area or is the data transformed in accordance with the file's embedded profile (if it exists and is valid) before populating Adobe's working area?
I've opened a file in ImageJ and the same file in PSE and their respective color pickers do agree, implying to me that the RGB data is not changed until editing commences or until the file is actually converted into another color space. But, still, I'm not sure about what's in Adobe's working area and therefore what is color-picked. Just the file data until changed? I'll bet Eric or Jeff knows ;)
I do have DCraw and can read the actual data from my Foveon raw files, perhaps there's a clue to be gained there. Also I have ExifToolGUI to check what embedded profile a file has, and ICC Profile Inspector for when I'm feeling brave . . .
thanks,
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Ted,
How photoshop deals with RGB numbers is customizable in color settings. The normal (and most sensible) setting is to preserve the embedded profile. This means that the embedded profile becomes the working space when you open the image. All the numbers you see in the photoshop color picker will be in relation to that space. So your ProPhoto TIF in your original question is brought in with RGB numbers unchanged and transformed in accordance with the file's embedded profile. No conversion to another space happens unless you explicitly ask for it (or have set you color settings to convert to the default space when opening images).
RAW files and Lightroom are a little different because RAW files aren't really in an RGB space until they have been converted from their RAW format. Lightroom handles this by converting the RAW internally to a space almost the same as ProPhoto RGB (Melissa RGB). The numbers you see in Lightroom are the RGB numbers in that space. When you export from Lightroom to a TIF or jpeg, only then does it get converted to a regular RGB space like sRGB, Adobe1998, etc.
Not sure if that answered the question…
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Ted,
How photoshop deals with RGB numbers is customizable in color settings. The normal (and most sensible) setting is to preserve the embedded profile. This means that the embedded profile becomes the working space when you open the image. All the numbers you see in the photoshop color picker will be in relation to that space. So your ProPhoto TIF in your original question is brought in with RGB numbers unchanged and transformed in accordance with the file's embedded profile. No conversion to another space happens unless you explicitly ask for it (or have set you color settings to convert to the default space when opening images).
Mark, I'm beginning to get it, I think. The confusion for me is that my version of Elements has limited stated color management. Anything other than sRBG and aRGB is not mentioned, but it will open a ProPhoto image without complaint and will actually save it thus profiled after editing. Classic Adobe . . . I'll bet it would take Adobe Wide if I tried.
I didn't fully get "RGB numbers unchanged and transformed" though. Does it mean that the numbers are transformed to a space, say ProPhoto, as part of the RAW conversion and then brought unchanged after the transformation into the, e.g. Melissa, working area along with the profile or knowledge thereof? Thus, our RAW yellow would be transformed into a D65 ProPhoto file as 234, 251, 84 and the profile says to the monitor profile "this is 100% saturated yellow in your space" which shows on the perfect screen as D65 sRGB 255, 255, 0.
RAW files and Lightroom are a little different because RAW files aren't really in an RGB space until they have been converted from their RAW format. Lightroom handles this by converting the RAW internally to a space almost the same as ProPhoto RGB (Melissa RGB). The numbers you see in Lightroom are the RGB numbers in that space. When you export from Lightroom to a TIF or jpeg, only then does it get converted to a regular RGB space like sRGB, Adobe1998, etc.
Not sure if that answered the question…
Yes, it does indeed. Especially the mention of 'Melissa' RGB. Not for Adobe the de facto ROMM standard, aka ProPhoto, gotta luv 'em . . . can't fault their business model, though!
I'm off to play with 3 different converters and see how they come with sRGB numbers for a reference pixel in my sunflower image. Well it's after dark and I'm retired so that would be fun in my world.
thanks again,