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Author Topic: Converting ProPhoto RGB to Adobe RGB - which Rendering Intent to use?  (Read 7418 times)

Dinarius

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....or is it image-specific?

Also, what about Black Point Compensation?

I want to create an action to convert a large folder of images - if that is possible.

Many thanks.

D.
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digitaldog

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Unless you find a V4 version profile you're going to be forced into a Relative Colorimetric intent no matter what you select. The ICC Profiles installed by Photoshop have only one table (Colorimetric). BPC should always be on. Toggle it on and off when soft proofing in Convert to Profile, I doubt you'll see a difference anyway with these two profiles.
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Doug Gray

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....or is it image-specific?

Also, what about Black Point Compensation?

I want to create an action to convert a large folder of images - if that is possible.

Many thanks.

D.
What Digital Dog said generally with a few minor things.

Adobe and PP both use matrix conversions with the installed profiles.

The only thing you have to really beware of and avoid is converting using absolute colorimetric intent and only then if you use Microsoft's Color engine, a setting you can select in Photoshop. Microsoft's color engine incorrectly does not color adapt and PP RGB v Adobe RGB have different white points resulting is a major color shift.

That said, the one thing you should be aware of is that when you convert from PP to Adobe RGB any colors that are in PP but are not in Adobe RGB will be clipped. Either to 255 or 0 and will undergo hue, saturation reduction and luminance change.

Color channels that are clipped to 0 will result in higher luminance. Colors that are clipped to 255 will result in lower luminance. However, you will not see a luminance change on your monitor because the monitor's profile will already have clipped PPRGB for displaying and no monitors currently out there have a large enough gamut that you would see this visually. You might see a change if you are soft proofing since clipped colors that are outside Adobe RGB will map to a printer's color differently. These effects are typically subtle though.

« Last Edit: July 28, 2016, 10:47:37 am by Doug Gray »
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Dinarius

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Many thanks for the replies.

I want to automate this process, if possible, since there are a lot of files.

Can I create an action that will open the files in one folder, convert them, and place the converted files in a new folder?

Not strictly relevant here, but........  8)

Thanks again.

D.
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rasworth

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You can create an action that opens one file, converts, and save as with a new name.  Then use the File > Automate > Batch command with suitable overrides to operate on an entire folder.

Richard Southworth

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bjanes

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Unless you find a V4 version profile you're going to be forced into a Relative Colorimetric intent no matter what you select. The ICC Profiles installed by Photoshop have only one table (Colorimetric). BPC should always be on. Toggle it on and off when soft proofing in Convert to Profile, I doubt you'll see a difference anyway with these two profiles.


Ver 4 sRGB profiles are available from the ICC, but are there any ver 4 AdobeRBG profiles?

If you do a RC conversion from ProPhotoRGB to AdobeRGB, you are unlikely to see any difference on your monitor, unless the gamut of your monitor is greater than that of Adobe/RGB. Current wide gamut monitors cover 98% to 99% of the AdobeRGB gamut, but there could be a gamut mismatch, where the gamut of the monitor is greater than Adobe RGB for some colors. It doesn't make any difference if the colors are clipped in the conversion or by the limited gamut monitor.

Bill
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digitaldog

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Ver 4 sRGB profiles are available from the ICC, but are there any ver 4 AdobeRBG profiles?
Not that I've ever seen. And I suspect you need one for ProPhoto RGB too. Kind of illustrates how well V4 profiles have been accepted in the last 10+years.
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Doug Gray

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Ver 4 sRGB profiles are available from the ICC, but are there any ver 4 AdobeRBG profiles?

If you do a RC conversion from ProPhotoRGB to AdobeRGB, you are unlikely to see any difference on your monitor, unless the gamut of your monitor is greater than that of Adobe/RGB. Current wide gamut monitors cover 98% to 99% of the AdobeRGB gamut, but there could be a gamut mismatch, where the gamut of the monitor is greater than Adobe RGB for some colors. It doesn't make any difference if the colors are clipped in the conversion or by the limited gamut monitor.

Bill

The V4 reference sRGB profile is quite interesting.  In perceptual mode it maps RGB values into a much wider gamut in PCS. You can see this by taking a ColorChecker image in standard sRGB, attaching the V4 sRGB reference profile, converting to ProPhoto using RelCol (so you can see what it does to the colors with Photoshop picker) then printing it, color managed normally. A large number of ColorChecker patches are increased in saturation well beyond the standard sRGB gamut.

In some ways it prints an sRGB colorchecker much like the built in printer driver when fed straight sRGB which is much more saturated than properly color managed.

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GWGill

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The V4 reference sRGB profile is quite interesting.  In perceptual mode it maps RGB values into a much wider gamut in PCS.
It likely maps to the PRMG. The assumption is that the destination profile maps from the PRMG to the destination device space.
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Doug Gray

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It likely maps to the PRMG. The assumption is that the destination profile maps from the PRMG to the destination device space.

The V4 reference sRGB profile has a large 3D LUT for Perceptual. For RI, it has a 3D LUT also but it is a single cube with 1D LUTs in and out and a matrix transform. The PI greatly expands the gamut to PRMG in the PCS. Their usage paper is described here:
http://www.color.org/ICC_White_Paper_26_Using_the_V4_sRGB_ICC_profile.pdf

There is detail on using Photoshop at the end of the paper which recommends the ROMM ICC profile, which is v4 compliant, unlike the standard sRGB. The large gamut ROMM profile contains this expanded PRM gamut which can then be printed or proofed. They have some pretty wireframe graphs showing the gamut expansion.

Rather amusingly, this V4 sRGB profile is labeled "beta" which was supposed to be removed after 6 months or so.  Didn't happen.

I will say that a few images I have from camera in sRGB do look attractive when printed after this gamut expansion and remapping. Colorimetric it isn't, of course but it is not supposed to be.


Interesting academic paper comparing V2 and V4 with actual printed images.
http://nicobonnier.free.fr/research/publications/CIC17_2009_Bonnier.pdf

Quote
One such development was the specification of a reference
color gamut, the Perceptual Reference Medium Gamut (PRMG)
adopted in 2005 in the first amendment to the version 4 of the
ICC specifications (v4). It was defined as an unambiguous reference
gamut to render, or re-render, to and from [1,6]. The shape of
the PRMG is similar to that of a gamut of a printing system, thus
quite different in shape from a reference display gamut.
« Last Edit: July 29, 2016, 05:48:22 pm by Doug Gray »
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digitaldog

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Re: Converting ProPhoto RGB to Adobe RGB - which Rendering Intent to use?
« Reply #10 on: July 29, 2016, 10:17:58 am »

I will say that a few images I have from camera in sRGB do look attractive when printed after this gamut expansion and remapping.
I hope these are images from a cell phone.  ;D
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Doug Gray

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Re: Converting ProPhoto RGB to Adobe RGB - which Rendering Intent to use?
« Reply #11 on: July 29, 2016, 10:42:26 am »

I hope these are images from a cell phone.  ;D

Yup. Really makes those look nice!  ;D

All in all it looks like an effort to pretty up the puny sRGB space.
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Dinarius

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Re: Converting ProPhoto RGB to Adobe RGB - which Rendering Intent to use?
« Reply #12 on: July 29, 2016, 02:41:24 pm »

Just to be sure...

When I create the ProPhoto to Adobe Action in CS6, do I choose Assign or Convert to Profile?

Many thanks.

D.
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rasworth

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Re: Converting ProPhoto RGB to Adobe RGB - which Rendering Intent to use?
« Reply #13 on: July 29, 2016, 02:49:19 pm »

Convert, assuming you want to retain the same colors.  If colors exist within your Pro Photo rendered images that are outside the Adobe 1998 gamut then they will be clipped to colors within the gamut.

Richard Southworth
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Doug Gray

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Re: Converting ProPhoto RGB to Adobe RGB - which Rendering Intent to use?
« Reply #14 on: July 29, 2016, 02:49:33 pm »

Just to be sure...

When I create the ProPhoto to Adobe Action in CS6, do I choose Assign or Convert to Profile?

Many thanks.

D.

Convert.  "Assign" is almost always the wrong thing to do in normal workflow except when importing an image that isn't tagged with a colorspace but you know what it is. Then you assign it. Never use assign to convert colorspaces.
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digitaldog

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Re: Converting ProPhoto RGB to Adobe RGB - which Rendering Intent to use?
« Reply #15 on: July 29, 2016, 06:02:47 pm »

Just to be sure...
When I create the ProPhoto to Adobe Action in CS6, do I choose Assign or Convert to Profile?
And why you don't want to use Assign: http://digitaldog.net/files/AssignConvert_Tutorial.pdf
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GWGill

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Re: Converting ProPhoto RGB to Adobe RGB - which Rendering Intent to use?
« Reply #16 on: July 29, 2016, 10:58:55 pm »

There is detail on using Photoshop at the end of the paper which recommends the ROMM ICC profile, which is v4 compliant, unlike the standard sRGB. The large gamut ROMM profile contains this expanded PRM gamut which can then be printed or proofed. They have some pretty wireframe graphs showing the gamut expansion.
That's the problem with the use of the PRMG in my view. If you want perceptual (i.e. compression only) rather than saturation intent (compression & expansion), you are out of luck.

You get a much better defined and accurate transformation using a device link or device profile with a source space specific perceptual (or whatever) gamut mapping, rather than relying on the PRMG fudge.
« Last Edit: July 30, 2016, 01:47:05 am by GWGill »
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Lundberg02

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Re: Converting ProPhoto RGB to Adobe RGB - which Rendering Intent to use?
« Reply #17 on: July 30, 2016, 12:03:39 am »

The best you can do is print ProPhoto from Photoshop using PS manages and the printer's perceptual.
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Doug Gray

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Re: Converting ProPhoto RGB to Adobe RGB - which Rendering Intent to use?
« Reply #18 on: July 30, 2016, 01:09:11 am »

That's the problem with the use of the PRMG in my view. If you want perceptual (i.e. compression only) rather than saturation intent (compression & expansion), you are out of luck.

You get a much better define and accurate transformation using a device link or device profile with a source space specific perceptual (or whatever) gamut mapping, rather than relying on the PRMG fudge.

That's the odd thing. The ICC sRGB reference perceptual profile doesn't compress, it mostly expands the gamut.

For instance in a colorchecker image the two colors most affected are cyan and yellow. If I set Photoshop to perceptual, attach the ICC v4 sRGB profile to a colorchecker card image that is in standard sRGB (only cyan is clipped in sRGB) then print it on Baryta SG canon 9500 II using perceptual both the cyan and yellow are printed with far more saturation than is possible in a standard sRGB gamut.

For instance the cyan patch comes out at Lab=(36, -29, -44) and the yellow patch prints at Lab=(83,13, 97).  Both of these are over 10 dE from the sRGB gamut boundary.

Basically, if you want color "Pop" from an sRGB image that profile is one way to get it. It happens because the PRMG is larger than sRGB so they re-map (expand) the sRGB gamut to the larger PRMG.

It's sort of like making a silk purse out of a sow's ear.
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GWGill

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Re: Converting ProPhoto RGB to Adobe RGB - which Rendering Intent to use?
« Reply #19 on: July 30, 2016, 01:55:49 am »

That's the odd thing. The ICC sRGB reference perceptual profile doesn't compress, it mostly expands the gamut.
It's not odd - that's the way it has to work. Introducing a defined intermediate gamut doesn't solve the problem that the source and destination gamuts are not simultaneously known to the gamut mapping. And without both, you can't know whether it's actually an expansion or compression. So you end up expanding the source gamut to the PRMG, and then compressing the PRMG to the destination gamut, resulting in a "saturation" type mapping. You mightn't notice if the source gamut mostly exceeds the destination (i.e. the case for a lot of the gamut for a display space to ordinary printing space), although there is excessive movement of colors that might result in inaccuracy, compared to the mapping situation where there is no PRMG involved.
Quote
Basically, if you want color "Pop" from an sRGB image that profile is one way to get it.
If I want "pop", I'll choose a saturation intent, not a saturation intent that is masquerading as a perceptual one.
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