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Author Topic: Out of Gamut unfixed, compresses all hues  (Read 18264 times)
bjanes
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« Reply #20 on: May 15, 2006, 11:29:02 AM »
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I suppose he wrote that for the sake of simplicity.

Photoshop doesn't do anything, it simply tells the relevant CMM what to do.

A matrix based profile primarily means that the corresponding colorspace (or device) acts linearly. It is completely irrelevant whether any tables are available. A CMM may create such tables from the linear matrix conversion if it wants to. It could emulate the conversion in a printer profile for example. That's irrespective of any image dependent conversion...
[a href=\"index.php?act=findpost&pid=65545\"][{POST_SNAPBACK}][/a]

I can't read Mr. Knoll's mind, but from what he said, I infer that the Adobe CMM requires look up tables to do perceptual rendering and these are not present in matrix profiles, hence no perceptual.

With my windows machine, I can also choose the Microsoft CMM. Apple users can also use the Apple CMM. When Windows Vista arrives with its new CMM (Kyuanos architecture), user written routines can be implemented and perhaps smart profiles such as you mention would be possible. For now, I don't think they are.
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« Reply #21 on: May 15, 2006, 11:45:49 AM »
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Note that the table in the Matrix profile is colorimetric so in theory you can select either Absolute or Relative. I only mention this because if you pick Absolute, it could look pretty ugly (but you can do this). Same table (the single table in that profile) but two possible results. This effect however appears to be CMM related. I just did a quick test with a file in Adobe RGB (1998). If you use Convert to Profile and select ColorMatch RGB using Adobe ACE and toggle from RelCol to Absolute, you see nothing but if instead you select Apple CMM, the Absolute option gives you an ugly blue cast. So it appears this is CMM is part of the picture and in light of what Thomas said, makes sense (at least with ACE). That is, ACE always uses RelCol even though you've asked for a different intent from the same table. Apple CMM does produce a white adjustment (more dangerous).
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« Reply #22 on: May 15, 2006, 01:00:50 PM »
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I have a proprietary CMM running here which only processes Matrix profiles. For RelCol it simply converts as ACE does using Channel clipping for out-of-gamut colors. However, when it is presented with Perceptual, it uses Color clipping instead. Really cool, because by simply switching intent, you can quickly compare results. Color clipping yields results which are much more akin to what a printerprofile would give.

Unfortunately, Photoshop doesn't use third-party CMMs for displaying, so it is useless to select the CMM in the ColorPreferences. As a matter of fact, talking about dangerous: you will get serious discrepancies between preview and mode-switch if you do that. (That includes the Apple CMM RelCol/AbsCol example mentioned).
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PeterLange
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« Reply #23 on: May 15, 2006, 04:35:03 PM »
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Perecetual rendering is not currently possible with matrix profiles ...
Some time ago I have written an Action as follows - for some *very* saturated flowers in Pro Photo RGB, in order to smoothen the conversion to sRGB. It could be worth a try – and for sure it can be improved:

/> Starting from an image / background layer ‘in’ ProPhoto RGB (16 bit):
/> Strg+A to select the whole image
/> Strg+C to copy the selection to the clipboard
/> Convert the image first to the profile ‘mini-sRGB-90’ (see below details)
/> Convert the image back to ProPhoto RGB
/> Add a New Layer on the top (Shift+Strg+N)
/> Strg+V to insert the copied selection (which still contains the original pRGB data)
/> Reduce the Opacity of this layer to e.g. 50% (negotiable)
/> Flatten the layers and Convert to regular sRGB

mini-sRGB-90 is distinguished from common sRGB by describing an even smaller gamut.  In detail, the R/G/B primaries were cut down by 10% towards the inner white point. Referring to above procedure, it’s the hard core so to speak. It can be created from regular sRGB via the Photoshop Custom Profile Function according to the specs as follows:
/> D65 white like with sRGB
/> 1.8 gamma to avoid unnecessary ups & downs
/> primaries are as follows:
Red: x = 0,6073 / y = 0,3299
Green: x = 0,3013 / y = 0,5729
Blue: x = 0,1663 / y = 0,0869

Hope it makes sense – Peter

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bjanes
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« Reply #24 on: May 15, 2006, 05:36:47 PM »
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Some time ago I have written an Action as follows - for some *very* saturated flowers in Pro Photo RGB, in order to smoothen the conversion to sRGB. It could be worth a try – and for sure it can be improved:

Hope it makes sense – Peter

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Peter,

It does seem to make sense. You define a space with a narrower gamut than sRGB and then convert to the narrow profile from ProPhotoRGB, clipping out of gamut colors. Then back to ProPhotoRGB and use opacity to effectively interpolate with the original image before converting to sRGB.

Couldn't you also use soft proofing also with ProPhotoRGB? Set the device to simulate to sRGB in the custom setup, show out of gamut colors, and then reduce the saturation until in gamut, and then convert from ProPhotoRGB to sRGB. I have some red flowers in ProPhotoRGB that are much out of gamut in sRGB and used the above method and noted that the maximum in the red channel of the converted file was near 255. The converted file looked pretty dull on screen, however.
« Last Edit: May 15, 2006, 05:37:02 PM by bjanes » Logged
PeterLange
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« Reply #25 on: May 17, 2006, 10:42:49 AM »
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Peter,

It does seem to make sense. You define a space with a narrower gamut than sRGB and then convert to the narrow profile from ProPhotoRGB, clipping out of gamut colors. Then back to ProPhotoRGB and use opacity to effectively interpolate with the original image before converting to sRGB.

Hi Bill,

Thanks a lot for your interest and for this concise summary!  I’m sorry for my late response (was out of the town yesterday); however, let me take the opportunity to outline some considerations more detailed:

The procedure as described above aims for a core/shell-structure with a solid core of unaltered colors and a compression range (in-between the narrower gamut and sRGB) which is intended to provide a smoother transition to the remaining (clipped) colors on the surface of sRGB.

This, sooner or later raises the question if channel clipping due to RelCol is inevitably something bad.  Above procedure in a modified, more extreme implementation can virtually squeeze a whole Granger Rainbow from ProPhoto RGB into sRGB, thus, avoiding channel clipping largely. But I could not find an example in practice where this makes a better image.

I think it’s a coin with two sides. Channel clipping of saturated colors due to gamut conversion indicates a loss of data-bits & information which can result in posterization and a missing fine structure. On the other side, in case that all out-of-sRGB pixels would be randomly distributed throughout the whole pRGB image (as opposed to clustered), channel clipping after conversion would just indicate a best possible use of the tiny gamut.
Further, given that two neighboring colors which both are clipped are not necessarily undistinguishable; real-world images probably more require an in-between approach (rather than an eliminate-clipping imperative).

Coming from ACR, it can make some sense to maintain ProPhoto RGB for final image editing (made my peace with it). A considerable part of my images contains more or less colors which are clearly located out-of-sRGB. Converting them to sRGB, plain RelCol seems to work fine in many cases. In essence, it’s an artistic decision to maintain a highest possible level of saturation at the cost of some channel clipping and even in case that some few details are ironed out at 400% magnification.

However, sometimes it gets too much; e.g. with very saturated flowers. That’s the intended field of application for above suggested procedure. But as we had a very long winter here in Europe (no flowers at all) it’s still more on a beta level. For example, it could make sense to add a hue-lock in order to avoid respective shifts resulting from CIE Lab as the profile connection space… Of course, I’d be glad if a dedicated cognoscenti would take up the subject.


Quote
Couldn't you also use soft proofing also with ProPhotoRGB? Set the device to simulate to sRGB in the custom setup, show out of gamut colors, and then reduce the saturation until in gamut, and then convert from ProPhotoRGB to sRGB. I have some red flowers in ProPhotoRGB that are much out of gamut in sRGB and used the above method and noted that the maximum in the red channel of the converted file was near 255. The converted file looked pretty dull on screen, however.
As far as I can tell, a global reduction of saturation bears three main risks. In 3D it can be understood as a squeezing of the whole de-facto gamut as occupied by the image colors. (1.) Possible in-sRGB colors are moved which could have been left where they are. (2.) pRGB colors which are just slightly out-of-sRGB are easily moved too far inside; there’s no threshold. (3.) Perceived lightness can be affected depending on the definition for saturation used.

Point number 1 can likely be solved e.g. by a selection of out-of-gamut colors via the Color Range tool. Maybe combined with a Hue/Sat.-layer in Saturation blend mode - this then also counteracts point number 3.  Or, it could make sense first to convert to Lab mode (for a stopover) where the Saturation slider of the Hue/Sat.-tool works differently (L* is preserved in Normal blend mode; no Saturation blend mode required).
But I think that point no. 2 is a persistent one.  It finally imposes the burden to balance ‘more details vs less saturation’ on a visual basis; because out-of-gamut-marks alone can be a bad advisor (see above discussion). The next problem is to handle this within a monitor’s limited gamut…

Finally I see a certain risk with this approach, to make things worse than better (‘file looked pretty dull’), but this shall not say that it couldn’t work well.


In summary, I tend to conclude that the whole issue of ‘ProPhoto RGB conversion to smaller matrix spaces’ is more pronounced in theory than in practice; depending on the photographic subject of course. So for such cases it would be quite nice to have a ready developed procedure and commonly agreed state of the art approach / Action which does the trick (unless I’m missing something which already exists).



Peter

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« Last Edit: May 17, 2006, 10:55:44 AM by PeterLange » Logged
Dennis
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« Reply #26 on: May 17, 2006, 09:29:39 PM »
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Now, I am a bit confused...

As far as I understood, the deal with ProPhotoRGB is the following:

There are colors, which a camera can capture, which are out of the gamut of sRGB (for example). So I process and convert the Raw data in ACR to ProPhotoRGB, which is big enough to enclose (most of the) camera's colors. Then I convert it to sRGB, and thus can keep the fine tonalities in the most saturated colors.

At this point, I am aware, that I lack some understanding of the whole process. A camera has no gamut, I once read, since otherwise there would be colors, it couldn't capture. Can one understand the capture of colors as kinda convertion from 'real' color to the gamut described by the camera's profile, using a colorimetric RI (color clipping)? If there's a profile for the camera, hasn't there to be a gamut, as well?

And how are the camera's colors transformed to the output color space inside ACR? Since very saturated colors can be clipped, if sRGB is chosen, it means that a colorimetric RI is used? And is it true, that the PCS inside ACR is ProPhotoRGB?

Now comes the point, which really confuses me: If you now have those very saturated colors in a file in PS with ProPhotoRGB and you convert it to sRGB, then the RI will always be colorimetric, right? Even if you chose perceptual. But colorimetric means clipping out of gamut colors, so where's the trick? If all colors outside from sRGB are clipped, you have no advantage. You'd need to map them via a perceptual rendering.

And would it then a bad idea, to assign sRGB to the ProPhotoRGB file (to keep all the numbers - nothing gets clipped), and then increase the saturation?

And what's the difference between channel clipping and color clipping?

Dennis.
« Last Edit: May 17, 2006, 09:32:23 PM by Dennis » Logged

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« Reply #27 on: May 18, 2006, 04:06:24 AM »
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Now comes the point, which really confuses me: If you now have those very saturated colors in a file in PS with ProPhotoRGB and you convert it to sRGB, then the RI will always be colorimetric, right? Even if you chose perceptual. But colorimetric means clipping out of gamut colors, so where's the trick? If all colors outside from sRGB are clipped, you have no advantage. You'd need to map them via a perceptual rendering.

Correct. Fortunately, you can use the softproof mode to judge the impact of a conversion. You can then desaturate or darken colors in ProphotoRGB so they will fit sRGB and therefore won't be clipped. That way you can preserve the original tonality and make up your own perceptual conversion.

If the original file did not have the tonalities to begin with, you wouldn't be able to do this.

See this text for a difference between channel clipping and color clipping.
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« Reply #28 on: May 18, 2006, 09:19:15 AM »
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Peter,

If you use a hue / sat adj layer you can use the eye dropper + and - tools to desat different colors to different extents until the out of gamut warning has gone.

You can also use the lightness and hue sliders for optimal control for your specific image.

When you have all the colors within the softproofed gamut then you need to use rel col rendering.

I think this allows you to maintain a customized rendering which can be tuned to the image

Ian

http://profiles.colourperfect.co.uk
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PeterLange
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« Reply #29 on: May 18, 2006, 03:16:05 PM »
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At this point, I am aware, that I lack some understanding of the whole process. A camera has no gamut, I once read, since otherwise there would be colors, it couldn't capture. Can one understand the capture of colors as kinda convertion from 'real' color to the gamut described by the camera's profile, using a colorimetric RI (color clipping)? If there's a profile for the camera, hasn't there to be a gamut, as well?

And how are the camera's colors transformed to the output color space inside ACR? Since very saturated colors can be clipped, if sRGB is chosen, it means that a colorimetric RI is used? And is it true, that the PCS inside ACR is ProPhotoRGB?
Dennis,

As far as I understand, this talk that cameras have no gamut is more a semantic issue:
http://luminous-landscape.com/forum/index....pic=10538&st=40

ACR was reported to use a linear gamma version of ProPhoto RGB as an intermediate working space. Not sure if a PCS is involved before or afterwards:
(D65/A interpolated matrix) input space >> 1.0 ProPhoto RGB >RelCol> selected output space

Recommended reading: Real World Camera Raw by Bruce Fraser.

Peter

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PeterLange
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« Reply #30 on: May 18, 2006, 03:27:14 PM »
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Peter,

If you use a hue / sat adj layer you can use the eye dropper + and - tools to desat different colors to different extents until the out of gamut warning has gone.

You can also use the lightness and hue sliders for optimal control for your specific image.

When you have all the colors within the softproofed gamut then you need to use rel col rendering.

I think this allows you to maintain a customized rendering which can be tuned to the image

Ian,

Let me assume that we’re somehow talking about a completely different scene.

A nice little flower can easily bear a considerable color saturation. Percentages of 90 to 100 % HSB-saturation in ProPhoto RGB are not an exception.

For the purpose of fair testing, let’s take a moderate RGB combo of 243, 116, 54. This color comes directly from red flower in front of me; it’s just 78% HSB-saturation. Everything referring to ProPhoto RGB.

Now install a Softproof to sRGB w/out-of-gamut marks.

Which settings of the Hue/Sat.-tool would you recommend to get rid of the out-of-gamut warning and to avoid channel clipping?

Peter

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bjanes
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« Reply #31 on: May 18, 2006, 04:53:51 PM »
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Ian,

Let me assume that we’re somehow talking about a completely different scene.

A nice little flower can easily bear a considerable color saturation. Percentages of 90 to 100 % HSB-saturation in ProPhoto RGB are not an exception.

For the purpose of fair testing, let’s take a moderate RGB combo of 243, 116, 54. This color comes directly from red flower in front of me; it’s just 78% HSB-saturation. Everything referring to ProPhoto RGB.

Now install a Softproof to sRGB w/out-of-gamut marks.

Which settings of the Hue/Sat.-tool would you recommend to get rid of the out-of-gamut warning and to avoid channel clipping?

Peter

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[a href=\"index.php?act=findpost&pid=65941\"][{POST_SNAPBACK}][/a]


I'm interested in Ian's reply also. I have a similar picture in ProPhotoRGB if anyone wants to give it a try. With my windows browser, the picture looks quite dull since the ProPhotoRGB profile is not being applied, so anyone saving it should assign the ProPhotoRGB profile if necessary.

[attachment=577:attachment]
« Last Edit: May 18, 2006, 04:57:42 PM by bjanes » Logged
Dennis
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« Reply #32 on: May 19, 2006, 06:21:59 AM »
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See this text for a difference between channel clipping and color clipping.
Quote
ACR was reported to use a linear gamma version of ProPhoto RGB as an intermediate working space. Not sure if a PCS is involved before or afterwards:
(D65/A interpolated matrix) input space >> 1.0 ProPhoto RGB >RelCol> selected output space

Recommended reading: Real World Camera Raw by Bruce Fraser.
Thanks for your answers. This book is already in my amazon wishlist, I'll have to buy it eventually...
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PeterLange
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« Reply #33 on: May 20, 2006, 04:45:36 AM »
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I'm interested in Ian's reply also. I have a similar picture in ProPhotoRGB if anyone wants to give it a try. With my windows browser, the picture looks quite dull since the ProPhotoRGB profile is not being applied, so anyone saving it should assign the ProPhotoRGB profile if necessary.

[attachment=577:attachment]
[a href=\"index.php?act=findpost&pid=65945\"][{POST_SNAPBACK}][/a]

Bill,

I’ve tried your image using my Action as suggested above. With an Opacity of 20%, final channel clipping after arriving in sRGB comes close to zero.

Compared to a straight conversion pRGB > RelCol> sRGB (bearing a lot of channel clipping), I don’t see any signs of image degradation.  So the good news (for me) is that my Action is apparently non-damaging.  That’s probably more than the Hue/Sat.-tool could ever reach.

However, now I find myself comparing both renditions at zig% magnification. Of course I’d be delighted to report that my hard-conceived Action - which can largely suppress channel clipping - offers a perceivable competitive edge.  But I’m not sure at all whether there’s an improvement in the sense of a preferred rendition, or not.  In fact, differences seem to be more measurable than visually graspable.


So the challenge seems to be quite simple:

Could anyone around here
render Bill’s image clearly better
to sRGB than plain RelCol ?

If yes, I’d be more than pleased to learn.
However, I'd expect more that this call will terminate this thread.

Peter

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skid00skid00
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« Reply #34 on: May 20, 2006, 09:42:43 AM »
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Wow, I never expected what I thought was a 'stupid' question (me being stupid), would provoke such a great thread!  

Thanks to all who participated!

Peter, since I've grown comfortable using LAB mode, I had the thought of mapping the gamut limits of my Epson R1800, and then seeing if I can develop  an A* and a B* curve that would keep the majority of colors unaltered, and just tweak the curve in the area of OOG to bring things back in gamut in a controllable way.  Thanks for the idea.

I'm in the process of calibrating my 1Ds with ACR's calibrate tab, and have run into the accurate blues/purples go neon blue problem, which I'm sure will also add complexity to this mess I'm in.  I'm thinking I'll need to set up a page describing what I've run into.

Thanks again to all!
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PeterLange
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« Reply #35 on: May 20, 2006, 01:23:07 PM »
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Thanks to all who participated!

Peter, since I've grown comfortable using LAB mode, I had the thought of mapping the gamut limits of my Epson R1800, and then seeing if I can develop  an A* and a B* curve that would keep the majority of colors unaltered, and just tweak the curve in the area of OOG to bring things back in gamut in a controllable way.  Thanks for the idea.

skid00skid00,

When the threadopener finalizes discussion, it’s typically over. So let me give you a little question on the way:

1.)  If a straight & proper RelCol conversion from ProPhoto RGB to smaller matrix spaces such as Adobe RGB or even down to sRGB somehow sets the standard
– which is very very hard to improve by any means, provided that we’re willing to jugde on a visual basis only, thus, ignoring all the channel clipping as indicated by the histogram (see above challenge)...

2.)  And given that the Lut of printer profiles can easily behave as the “invisible elephant in the ICC print-rendering room”, in particular when you try to feed him with saturated colors from ProPhoto RGB (and whether you try RelCol or Perceptual)… http://www.prophotocommunity.com/ubbthread...page/page//vc/1

... what would be the conclusion?  

Cheers! Peter

P.S.: Yes, in the meantime I’m using ProPhoto RGB for final image editing (coming from ACR it’s convenient, good for archieving, and some key settings are applied very properly in ACR on a linear gamma basis anyway).  But when it comes to print, bigger is not always better... (at least in the sense of simplicity).
« Last Edit: May 20, 2006, 01:25:58 PM by PeterLange » Logged
Dennis
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« Reply #36 on: May 20, 2006, 03:43:31 PM »
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I’ve tried your image using my Action as suggested above. With an Opacity of 20%, final channel clipping after arriving in sRGB comes close to zero.
Peter,

if I understood your action correctly, you are using Mini-sRGB-90 in order to get some headroom for the fine tonalities in the very saturated colors, right? Converting to mini-sRGB clips a pretty amount of saturated colors, and gives you a bit space to work for sRGB. So with the opacity of the again pasted pRGB, you just control how much fine detail and color you add to the clipped mini-sRGB colors. Did I get it right?

I implemented and tried your action as described above, but with 20% opacity, I came to a result inferior to the straight conversion, from a visual standpoint.

I tried Bill's approach as well, and ended up with a better result. As he told, I activated the gamut warning and reduced the saturation. In the beginning I desaturated the image globally, which led to a dullish image - just like Bill said. Since only the very saturated colors are critical, I was looking for a way to reduce the saturation not evenly - like 'Hue/Saturation' does - but more in a curved manner: Reduce the very saturated more than the less saturated colors. Ideal would be a mask representing the grades of saturation of the image, like the S channel in the HSB system. Any clou, how to do that? I helped myself with Select>Color Range... and found it useful, to select the yellows and apply this selection as a layer mask for a Hue/Saturation adjustment layer. So I was able to bring the OOG colors back into play without reducing the overall saturation too dramatically. Then, with the image converted to sRGB, I figured out, that bringing up the global saturation clips the colors too quickly, so I went the same way in the other direction: I used the color range selection in inverted mode and applied it to an adjustment layer.

Best Regards,
Dennis
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« Reply #37 on: May 21, 2006, 10:50:53 AM »
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skid00skid00,

When the threadopener finalizes discussion, it’s typically over. So let me give you a little question on the way:



Ummm, 42?

And for the record, it wasn't my intention to close the thread... I just wanted to thank everyone before the discussion ended!

What I've taken from this thread is that we really don't know what will come thru the color pipeline, until it hits the paper...  I've certainly seen that the more I push the hue/sat/contrast envelope, the more trouble I have getting exactly what I want.

As an aside, Peter, I'm capturing with an extreme form of shoot-to-the-right by having modified the in-camera curve and using the widest available colorspace.  These are both applied to the thumbnail that the camera uses to create the histogram.

I then use ACR into ProPho at 8 bits (because I'm running a 1GHz PC w/512MB, and even setting PS to retain no history, and keeping my adj. layers to only ONE, the PC is sloooow.   BTW, I use the crop dropdown in ACR to give me an out-of-ACR image size of 6840 x 4551 for my 13" x 19" prints.

I've yet to see any banding issues, even though I use per-channel contrast expansion in RGB mode, then boost saturation variance in LAB by steepening the A and B curves.

I tried to replace the ColorMatch space that ACR uses, with a space from my camera, but was unsuccessful.  I *think* what I really want to do is create a linear working space that's the same 'size' as my printer, and then convert from ProPho into that within PS.  But that's going to be 9-18 months in the future...

For now, I need to get a handle on why I need four different ACR calibrate settings files to get the correct hue/sat under different lighting conditions (all sunlight).  I may have pushed through the 'envelope' with my setup...
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« Reply #38 on: May 21, 2006, 01:48:48 PM »
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skid00skid00,

Don’t get me wrong; I was just trying to focus discussion on a first milestone:

If someone around here would be in the position to convert Bill’s flower clearly better from ProPhoto RGB to sRGB than straight RelCol (!?).  If yes, please just post the resulting image, plus a step by step description of the procedure. And no, further artistic image editing after arriving in sRGB was not meant to be part of the challenge.

Note, in order to avoid wrong conclusions, please ensure that you’re not operating out-of-the-gamut of your monitor (which happens even with sRGB).  If yes, you might wish to visit the main Color settings tab. There’s an option to de-saturate monitor colors (‘Sättigung der Monitorfarben verringern’) in order to show all the possibly hidden details.

Peter

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P.S.: If of help, here’s my way to accomplish ACR calibration.
http://www.adobeforums.com/cgi-bin/webx/.3bbf4d7a/0
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« Reply #39 on: May 21, 2006, 04:13:10 PM »
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If someone around here would be in the position to convert Bill’s flower clearly better from ProPhoto RGB to sRGB than straight RelCol (!?).  If yes, please just post the resulting image, plus a step by step description of the procedure.

Hello Peter,

Shouldn't you at least try to define what you mean by better? (I don't mean scientifically, but in this particular case).

The preview of the image is a clunky clipped file. If you convert this to sRGB with standard relcol, then you simply get what you see (assuming of course that your monitor behaves somewhere in the sRGB ballpark).

The fact that the red and yellows are not displaying in their correct hues on most monitors due to this clipping is then somewhat irrelevant. An interesting comparison may result from converting to a printer profile. And if you are going to choose some contorted way of converting to sRGB using multiple profiles, might I suggest trying a decent Epson profile as an intermediate space?

This will allow you to convert Perceptually to a smaller space, including hue constancy, and allows for the greatest correlation between what you see and what you print, no?
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Oscar Rysdyk
theimagingfactory
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