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Author Topic: Perceptual rendering intent – matrix to matrix – is it possible now ?  (Read 7101 times)
tho_mas
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« Reply #20 on: January 16, 2011, 10:00:10 AM »
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That's commonly understood, however, with these profiles i.e. PRMG_RGB (or sRGB_v4) being used as the source space, we just did not want to exclude 'anything' in the course of testing.  If only the target space needs to include a perceptual table, which is what conventional wisdom suggests, I'm wondering why we ever started to convert to ISO22028-2_ROMM-RGB first, before targeting the smaller PRMG_RGB (or sRGB_v4) spaces. Anyway.
ah, okay, I got it!
Well, I think both profiles must provide a perceptual table... but at least the target profile.

What happens when you convert perceptual from ISO22028-2_ROMM to Lab and then relcol+BPC to sRGB?

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Peter_DL
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« Reply #21 on: January 16, 2011, 10:42:46 AM »
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ah, okay, I got it!
Well, I think both profiles must provide a perceptual table... but at least the target profile.

What happens when you convert perceptual from ISO22028-2_ROMM to Lab and then relcol+BPC to sRGB?

ISO22028-2_ROMM-RGB
-> RelCol or Perceptual to Lab
… makes no difference, it’s apparently the same.

I’m hearing you regarding PhotoGamut RGB,
whereas however all these ICC (v4, whatsoever) profile variants seem to be a dead end in the context of this thread - unless I’m still missing something.

Peter

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tho_mas
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« Reply #22 on: January 16, 2011, 10:59:39 AM »
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I’m hearing you regarding PhotoGamut RGB,
whereas however all these ICC (v4, whatsoever) profile variants seem to be a dead end in the context of this thread - unless I’m still missing something.
I don't know about the state of the development and implementation of V4 profiles. I don't use those profiles; actually I do not even use matrix profiles (other than my monitor profile and sRGB for web purposes... but for 600x450px small images on the web I don't care about clipping).
Photogamut works like an oversized printer profile (actually it is a printer profile, technically speaking)... this is why perceptual is available here (and actually works really well). Regarding it's original target (encompassing all printers) it's a bit dated (today some printers provide larger gamuts)... but as an intermediate color space to go to sRGB or similar purposes it's still very useful.
 
« Last Edit: January 16, 2011, 11:05:34 AM by tho_mas » Logged
Peter_DL
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« Reply #23 on: January 16, 2011, 11:12:07 AM »
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... Current perceptual rendering is not very smart, since it compresses the gamut of an image even if the image contains no out of gamut colors in the destination space.

However, rendering from scene referred to output referred is not a simple process as explained by an excellent paper by Karl Lang ...

We still find this astonishing (or sometimes annoying):  there are many dedicated tools and sliders to facilitate a perceptual compression along the tonal scale, in order to render tonality from scene to output dynamic range - talking about Brightness & Contrast sliders, a Parametric Tone Curve, or selection-based 'HDR' techniques for tone mapping, etc.

Whereas there seems to be much less support for the orthogonal dimension i.e. color saturation, when we try to facilitate a perceptual compression of scene saturation via Raw / ProPhoto RGB into tiny sRGB - e.g. for a simple Frontier lab print.

Regards,

Peter

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Peter_DL
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« Reply #24 on: January 17, 2011, 09:38:14 AM »
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Photogamut works like an oversized printer profile ... this is why perceptual is available here (and actually works really well). Regarding it's original target (encompassing all printers) it's a bit dated (today some printers provide larger gamuts)... but as an intermediate color space to go to sRGB or similar purposes it's still very useful.

Supplementary:

The left image was converted from ProPhoto RGB, relcol to sRGB.
As shown in post #2 there's a perceivable loss of image details.

The right image was converted from ProPhoto RGB, perceptual + bpc to PhotoGamut RGB.
Then, a Local Contrast Enhancement was applied through an inverted Saturation Mask.
Finally the file was converted relcol to sRGB as well.

For the purpose of showing it here, the screenshot was pasted in a new file, monitor profile was assigned and then converted to sRGB again.

Peter

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« Last Edit: January 17, 2011, 09:53:45 AM by Peter_DL » Logged
tho_mas
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« Reply #25 on: January 17, 2011, 01:19:21 PM »
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yep, the PhotogamutRGB version looks much better.
If I would work in ProPhoto I would most likely use PRMG_RGB (or Photogamut) as gamut warning profile (preview off / colour warning on).
Not to edit the files so that they always fit into PRMG_RGB... but just to be warned.
Likewise I use my monitor profile as proof profile (preview off / colour warning on)... so that I can see what I can not see  Roll Eyes
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Schewe
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« Reply #26 on: January 17, 2011, 01:51:30 PM »
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The right image was converted from ProPhoto RGB, perceptual + bpc to PhotoGamut RGB.
Then, a Local Contrast Enhancement was applied through an inverted Saturation Mask.
Finally the file was converted relcol to sRGB as well.

Well, to fill out the side by side, you should have used the same procedure to do a local contrast enhancement on the ProPhoto RGB prior to transforming to sRGB using RelCol. As it is, the second image is indeed better but who's to say it's because of perceptual mapping or the contrast work? As it is now, it's kinda apples/oranges.
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digitaldog
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« Reply #27 on: January 17, 2011, 01:52:53 PM »
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Well, to fill out the side by side, you should have used the same procedure to do a local contrast enhancement on the ProPhoto RGB prior to transforming to sRGB using RelCol. As it is, the second image is indeed better but who's to say it's because of perceptual mapping or the contrast work? As it is now, it's kinda apples/oranges.

My thoughts exactly.
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Andrew Rodney
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tho_mas
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« Reply #28 on: January 17, 2011, 02:26:42 PM »
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you should have used the same procedure to do a local contrast enhancement on the ProPhoto RGB prior to transforming to sRGB using RelCol.
"you should have ..." :-))
the initial question was whether or not there is an sRGB profile providing perceptual RI. Period. There is none; at least none that works as supposed to. Period.
PhotogamutRGB as intermediate colour space provides perceptual RI and therfore works excellent as a workaround for this particular issue.
Of course you can do a lot of things with curves, saturation, masks and you name it. But that was not the question here.

Quote
As it is now, it's kinda apples/oranges.
Not so!
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Schewe
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« Reply #29 on: January 17, 2011, 02:34:27 PM »
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"you should have ..." :-))
the initial question was whether or not there is an sRGB profile providing perceptual RI. Period. There is none; at least none that works as supposed to. Period.

No, not period...if you are going to do ANY post processing of any kind on one test image then you must do the same post on the other test image...

You CAN (and I often do) tweak an image in ProPhoto RGB while soft proofing in sRGB to massage and manipulate the conversion prior to actually converting. It's not the same as a more automated color transform using perceptual but it does offer control over the way the RelCol will impact the conversion.
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tho_mas
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« Reply #30 on: January 17, 2011, 02:38:41 PM »
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No, not period...if you are going to do ANY post processing of any kind on one test image then you must do the same post on the other test image...
hups... I completely missed the part that there was further editing on the second image!
Sorry!!
Well, this is indeed apples to oranges...
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Schewe
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« Reply #31 on: January 17, 2011, 04:27:13 PM »
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hups... I completely missed the part that there was further editing on the second image!
Sorry!!

No problem...although I do happen to think the same post on the PP RGB image before going to sRGB in RelCol could have helped the results a bit. Which was why I though it was Apples to Oranges...
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Peter_DL
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« Reply #32 on: January 17, 2011, 04:41:14 PM »
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You CAN (and I often do) tweak an image in ProPhoto RGB while soft proofing in sRGB to massage and manipulate the conversion prior to actually converting. It's not the same as a more automated color transform using perceptual but it does offer control over the way the RelCol will impact the conversion.

No step was hidden,
it’s an open source (see attachment).

Peter

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Schewe
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« Reply #33 on: January 17, 2011, 05:27:22 PM »
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No step was hidden,
it’s an open source (see attachment).

But the point is that you did additional post processing to the second image that wasn't duplicated in any manner in the simple PP RGB to sRGB transform...one CAN (and should) soft proof a PP RGB image in sRGB prior to transform if you want to see what's gonna happen to color saturation and detail and do something about before doing the transform.
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tho_mas
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« Reply #34 on: January 17, 2011, 07:26:46 PM »
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No problem...although I do happen to think the same post on the PP RGB image before going to sRGB in RelCol could have helped the results a bit. Which was why I though it was Apples to Oranges...
on the other hand he first  converted perceptual to Photogamut and afterwards applied further adjustments. If there is already clipping in the converted file, there's not so much to improve with further editing...
Photogamut is very useful to map in particular bright high saturated colours into the range of sRGB (respectively in the range of printable colours)... so if you just want to "compress" the colours of an image without clipping it's an easy workflow (especially when you have to convert a number of different images...).
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