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Author Topic: Srgb and Adobe RGB some beginners questions  (Read 11928 times)
sanfairyanne
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« Reply #20 on: June 22, 2012, 05:54:55 AM »
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Thank you Simon and Tony, you're advice is most appreciated, I'm will get the tutorial ASAP. I'm in a manic rush with work but will no doubt want to come back and ask more questions it's great to have your help.

Regards Andrew
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digitaldog
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« Reply #21 on: June 23, 2012, 10:36:33 AM »
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Lightroom uses ProPhoto RGB in Develop Module.  (Actually, a variant of ProPhoto with linear gamma for editing, but sRGB gamma for the histogram).  So in Develop Module, the image displayed on the monitor is in ProPhoto RGB colour space.

The processing is ProPhoto primaries with a 1.0 TRC ‘gamma’ but what is previewed is Adobe RGB (1998). The processing in all modules is again this variant of ProPhoto. Untagged rendered images are assumed to be in sRGB.

The key to getting everything in Photoshop to sync up with what LR feeds it is simply having the color policies set to preserve.
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Andrew Rodney
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« Reply #22 on: June 23, 2012, 12:46:59 PM »
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The processing is ProPhoto primaries with a 1.0 TRC ‘gamma’ but what is previewed is Adobe RGB (1998). The processing in all modules is again this variant of ProPhoto.
In Develop Module, what is displayed appears to be ProPhoto RGB, not Adobe RGB.  I have a wide-gamut monitor which is a bit wider than Adobe RGB, so I can see that quite clearly. 

The previews, used in Library and elsewhere (but not in Develop Module), are Adobe RGB.  I assume that's what you meant?
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digitaldog
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« Reply #23 on: June 23, 2012, 01:26:14 PM »
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Previews are Adobe RGB:
http://help.adobe.com/en_US/lightroom/using/WS268F3399-80B2-4169-A598-04C7F769FFA0.html
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Andrew Rodney
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« Reply #24 on: June 23, 2012, 02:30:01 PM »
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Curious.  That link says: "the Develop module also displays photos in the Adobe RGB color space", but I don't believe it's doing that on my machine!  I've created some colour patches in ProPhoto RGB with pure primary colours.  That is Red: R=100%, G=0%, B=0% etc.  On my wide-gamut monitor which is a bit wider than Adobe RGB, these patches appear markedly more saturated in Develop Module than in Library.  By contrast, the same patches with pure colours in Adobe RGB look the same in Develop and Library.  I think the Develop Module doesn't display the Adobe RGB previews, but displays directly the ProPhoto image.  I think that help file is probably not correct.  I know I've read before that Develop displays ProPhoto RGB, and I'll try to track down a link. 
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digitaldog
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« Reply #25 on: June 23, 2012, 02:41:30 PM »
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Curious.  That link says: "the Develop module also displays photos in the Adobe RGB color space", but I don't believe it's doing that on my machine! 

Well your machine is therefore unique <g>.

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I know I've read before that Develop displays ProPhoto RGB, and I'll try to track down a link. 

That is incorrect but sure, let’s see where that came from. Now way back in say 2008 (around LR2), there was a time when the previews may have been in ProPhoto, no longer.
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Andrew Rodney
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« Reply #26 on: June 23, 2012, 02:56:53 PM »
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Well your machine is therefore unique <g>.

That is incorrect but sure, let’s see where that came from. Now way back in say 2008 (around LR2), there was a time when the previews may have been in ProPhoto, no longer.
I've thought about it some more and re-read your post, and I think we're talking at cross purposes.

Previews are Adobe RGB, no argument.  That's because they're stored in jpeg format, and using a very wide colour space in 8-bit data isn't a good idea (you get large tonal steps).

However, in Develop Module, LR isn't using the previews.  It's displaying the image data that it's editing, rendered from the ProPhoto RGB image data in real time.  This is why there are sometimes differences between what's displayed in develop module and library.  For example in LR3, sharpening and noise reduction were not always shown in develop module except at 1:1 zoom.  This was to save processing time.  In library module, processing time isn't an issue as what is being displayed is a pre-prepared preview.  

Or are you saying that in Develop Module, LR makes takes each edit you do, re-renders the image and updates the preview in real time each time you make any adjustment?  After each edit or movement of a slider, it converts the entire image to Adobe RGB, converts to jpeg, stores the preview, converts it back from jpeg, and colour-manages the preview to thedisplay?  Wouldn't it be simpler to simply colour-manage the ProPhoto image to the display?  And then update the preview only once, next time you access it in Library Module?  

I think the latter is what happens.  

Anyway, I've launched a thread in http://forums.adobe.com/community/lightroom in the hope that someone from Adobe might settle the question. 
« Last Edit: June 23, 2012, 03:11:37 PM by Simon Garrett » Logged
digitaldog
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« Reply #27 on: June 23, 2012, 03:35:06 PM »
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Previews are Adobe RGB, no argument.  That's because they're stored in jpeg format, and using a very wide colour space in 8-bit data isn't a good idea (you get large tonal steps).

Correct and the reason why ProPhoto isn’t used any more.

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Or are you saying that in Develop Module, LR makes takes each edit you do, re-renders the image and updates the preview in real time each time you make any adjustment?
 

As opposed to doing nothing? Not updating? Yes, it is updating each time you do something or this would be a difficult way to edit images <g>.

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After each edit or movement of a slider, it converts the entire image to Adobe RGB, converts to jpeg, stores the preview, converts it back from jpeg, and colour-manages the preview to thedisplay?  Wouldn't it be simpler to simply colour-manage the ProPhoto image to the display?  And then update the preview only once, next time you access it in Library Module?  

You’d have to get an Adobe engineer to comment on that simplicity issue. But it seems pretty clear thus far that the previews in Develop are Adobe RGB (1998) and I have to assume that yes, they are shown to you (or why have it?).
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Andrew Rodney
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« Reply #28 on: June 23, 2012, 04:13:59 PM »
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I'm obviously not making myself clear, sorry about that.

Previews are Adobe RGB, no argument.  Previews are created when you first view an image in Library Module (or first time after the image has been edited in Develop Module).  They are cached and stored in Lightroom's preview cache.  

But I don't think they are used to display the image in Develop Module.  Develop Module (I think) renders the image from the ProPhoto RGB working space image (you agree that Lightroom uses ProPhoto RGB as its working space?).  

That's why I don't think LR needs to update the previews after each edit operation.  Because it's not using them at that point.  It doesn't need the preview until next time you go to Library Module (or any module other than Develop).  In Develop Module it updates the display in real time, obviously, but not the preview.  I think it's rendering the ProPhoto RGB working space image data directly to the display (using colour management, obviously, mapping to the monitor colour space by means of the image profile and monitor profile in the usual way).  

So:
Library Module (and other modules except Develop): LR renders the cached Adobe RGB jpeg preview image.  
Develop Module: LR renders directly from the ProPhoto RGB image data.

You may not agree with me, but I hope I'm making myself clear.  And I'll be quick to own up to my error if anyone from Adobe tells me so.  Or if you can explain why the image rendered in Develop Module is visibly different to the image rendered in Library Loupe view, if they're both using the same preview image!

I'm trying to find references about the differences in rendering between Develop and Library modules.  I've found quite a number discussing that the image as rendered in Develop isn't always the same as the image rendered in Library.  I infer from this that Develop doesn't simply render the preview, or the image would look the same.  See for example: http://forums.adobe.com/message/3498280#3498280, http://forums.adobe.com/thread/889490?tstart=30.  

PS - edited to add:

To illustrate what I mean: here are two screen captures of 100% saturated colours in a ProPhoto RGB image.  The first is a screen shot of the view in Develop Module, the second is the view in Library Module.  Obviously the colour spaces are mangled in the screen capture, but the point is: the images are different.  The screen shot in Develop Module has more saturated colours, which you'd expect if Develop Module is displaying in ProPhoto RGB while the Library Module is displaying in Adobe RGB (the preview image).  And, of course, the monitor has to have a colour space wider than Adobe RGB, otherwise you wouldn't see the difference.  
http://www.simongarrett.co.uk/CaptureProPhotoDevelop.JPG
http://www.simongarrett.co.uk/CaptureProPhotoLibrary.JPG
« Last Edit: June 23, 2012, 04:47:33 PM by Simon Garrett » Logged
digitaldog
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« Reply #29 on: June 23, 2012, 05:34:23 PM »
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But I don't think they are used to display the image in Develop Module.  Develop Module (I think) renders the image from the ProPhoto RGB working space image (you agree that Lightroom uses ProPhoto RGB as its working space?).

Generally it renders from raw data (which has no defined color space) and certainly isn’t ProPhoto RGB. Sometimes it renders from sRGB or whatever is the original data color space. That the processing data path uses ProPhoto with 1.0 TRC is one thing. That the color space of what it shows you is Adobe RGB (1998) as specified in the newer Adobe doc (and info I have from Adobe) is another thing. On top of all that, the values and histogram are clearly not ProPhoto RGB unless you invoke soft proofing and select that as an option. The quality of the preview you see in Develop is absolutely different in how it is produced and shown to you compared to other modules, but the question is, what is the color space of that data? Unless the engineers posting to me have changed something, in LR4 it is Adobe RGB (and has been that way for awhile).
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Andrew Rodney
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Tony Jay
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« Reply #30 on: June 23, 2012, 06:15:35 PM »
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Andrew, thank you for clarifying and defining the various shades of grey (pun intended) in the world of how Lightroom uses and renders the various colour spaces in its domain.

Hopefuly that dizzy feeling will now abate.

Regards

Tony Jay
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Simon Garrett
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« Reply #31 on: June 23, 2012, 06:37:13 PM »
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...but the question is, what is the color space of that data? Unless the engineers posting to me have changed something, in LR4 it is Adobe RGB (and has been that way for awhile).
I don't think that's correct for Develop Module, and I can demonstrate on my monitor that Develop and Library module are probably not using the same colour space.  However, we've done this to death both here and on the Adobe forum so let's agree to differ! 

With any luck, someone from Adobe will post there and confirm which of us is right. 

Best regards,

Simon Garrett.
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