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Author Topic: New Photoshop CC 2017 gamma options - which to use with Lightroom?  (Read 1821 times)

Ad_Astra

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I have noticed in Photoshop CC 2017 under Color Settings there is a whole new range of gamma settings to use with ProPhotoRGB, sRGB etc. You can select from a gamma of: 0.75, 1, 1.2, 1.4, 1.5, 1.8, 2.0, 2.2, 2.5, 3.0

I have two questions on this:

1) In Lightroom and ACR I understand that they use "Melissa RGB" which is ProPhoto gamut and a gamma of 2.2. I assumed Photshop did the magic and converted to the original ProPhoto RGB gamma 1.8 when movonmg from Lightroom to Photoshop. Now we have a ProPhoto RGB gamma 2.2 should I use this as the default color space in Photoshop? It sounds better to me as there is no gamma conversion step.

2) What use are these new gamma settings for? Is there an application in photography for these?

Many thanks


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Dave Ellis

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #1 on: February 05, 2017, 10:52:51 PM »

I have noticed in Photoshop CC 2017 under Color Settings there is a whole new range of gamma settings to use with ProPhotoRGB, sRGB etc. You can select from a gamma of: 0.75, 1, 1.2, 1.4, 1.5, 1.8, 2.0, 2.2, 2.5, 3.0

I have two questions on this:

1) In Lightroom and ACR I understand that they use "Melissa RGB" which is ProPhoto gamut and a gamma of 2.2. I assumed Photshop did the magic and converted to the original ProPhoto RGB gamma 1.8 when movonmg from Lightroom to Photoshop. Now we have a ProPhoto RGB gamma 2.2 should I use this as the default color space in Photoshop? It sounds better to me as there is no gamma conversion step.

2) What use are these new gamma settings for? Is there an application in photography for these?

Many thanks

My understanding is that LR/ACR uses PhotoPro RGB with a gamma of 1 (linear) in the editing space and Melissa (PhotoPro RGB with an sRGB gamma curve, roughly 2.2) for histogram display. Accordingly, it shouldn't matter what gamma you use in your PS Colour settings as when you export the image to PS from LR or ACR, it will involve a direct linear to gamma conversion rather than a conversion from one gamma value to another. If you are going to use ProPhoto RGB in PS, I think you'd be better off sticking to the standard gamma of 1.8 for that color space.

As for your second question, I'm afraid I don't know and can't think why these gamma choices have been introduced.

Dave
« Last Edit: February 05, 2017, 11:13:52 PM by Dave Ellis »
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Simon J.A. Simpson

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #2 on: February 07, 2017, 12:54:36 PM »

I have noticed in Photoshop CC 2017 under Color Settings there is a whole new range of gamma settings to use with ProPhotoRGB, sRGB etc. You can select from a gamma of: 0.75, 1, 1.2, 1.4, 1.5, 1.8, 2.0, 2.2, 2.5, 3.0

I've looked for these and cannot find them under ‘Color Settings’.  Could you say where these are to found in the panel.

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Ad_Astra

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #3 on: February 07, 2017, 02:14:07 PM »

Apologies, it is my mistake. I have a plug-in that uses false profiles. I was wondering why this hadn't cropped up before. All the ProPhoto RGB profiles I see with different gamma were installed by the plug-in. I guess in CC 2017 it is the first time I have had to revisit the color profiles page in a while which totally confused me with multiple ProPhoto RGB profiles.

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Simon J.A. Simpson

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #4 on: February 07, 2017, 02:53:03 PM »

Ad.  Not at all…  Glad we cleared that up.

All the best.
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Jim Kasson

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #5 on: February 07, 2017, 04:17:17 PM »

I have noticed in Photoshop CC 2017 under Color Settings there is a whole new range of gamma settings to use with ProPhotoRGB, sRGB etc. You can select from a gamma of: 0.75, 1, 1.2, 1.4, 1.5, 1.8, 2.0, 2.2, 2.5, 3.0

I have two questions on this:

1) In Lightroom and ACR I understand that they use "Melissa RGB" which is ProPhoto gamut and a gamma of 2.2. I assumed Photshop did the magic and converted to the original ProPhoto RGB gamma 1.8 when movonmg from Lightroom to Photoshop. Now we have a ProPhoto RGB gamma 2.2 should I use this as the default color space in Photoshop? It sounds better to me as there is no gamma conversion step.

2) What use are these new gamma settings for? Is there an application in photography for these?

I see the confusion has been cleared up (including the Lr gamma's being unity), so I'll just deal with your last question. Changing the gamma changes the potential for rounding errors, contouring, and artifacts. However, if you are using 15 bit precision or greater, that is usually not a problem in Ps.

Changing the gamma will change the way that layers blend, in many cases. It will also change the visual effect of arithmetic operations among layers. It can also change the visual effect of curves.

If you're using PPRGB for your editing space, I'd advise you to stick with the default gamma (1.8), unless you have a specific reason for doing otherwise. The most common gamma other than the default gamma is one, but even that is unusual.

Jim

Redcrown

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #6 on: February 07, 2017, 11:59:24 PM »

This business of "gamma", and the Photoshop color settings for Gray Working Spaces in particular has always confused me.

When processing RGB images in Photoshop, I can't see how the Gray Working Space makes any difference. I've done a lot of tests to try to find a difference. None found. So, please describe a test we can all do that demonstrates a difference.

Example 1: I open an RGB image and drop in some sample points. Then I cycle trough various Gray Working Spaces. There is no visible difference on screen, there is no change in the RGB values of the sample points. Same result in sRGB, Adobe98, and ProPhoto. Same result in 8bit and 16bit.

Example 2. I open an RGB image with the Gray Working Space set to Gray Gamma 2.2. I apply a strong Curves adjustment layer, flatten and save as Version 1. Then I repeat with Gray Working Space set to Dot Gain 20%, which is the default for my Photoshop. Same image, same Curves adjustment, flattened and saved as Version 2.

Then I load Version 1 and Version 2 as layers, put the top layer in Difference mode, and check the Histogram StdDev value. It's zero. No difference. Again, the same "no difference" result regardless of RGB working space and bit depth. I've repeated this test with different types of adjustment layers, never finding a difference.

Example 3. I open an RGB image, drop some sample points, and dupe it. With Gray Working Space set to Gray Gamma 2.2, I convert one copy to grayscale via Image/Mode/Grayscale. The I change the Gray Working Space to Dot Gain 20% and convert the second copy to grayscale.

The images look identical on screen, but the sample points (K% values) are now quite different. Why is that? How come different sample point values produce the same on-screen values. I convert both these images back to RGB mode, and Voila!, the sample points are the same again.
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Schewe

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #7 on: February 08, 2017, 01:07:38 AM »

When processing RGB images in Photoshop, I can't see how the Gray Working Space makes any difference. I've done a lot of tests to try to find a difference. None found.

The Gray Working Space has no direct impact on RGB images...the Gray Working Space only impacts grayscale images. The only way an RGB image will be modified by the Gray Working Space is when converting from RGB to grayscale.

I set my Gray Working Space gamma to match that of my RGB working space... for PP RGB 1.8 and for ARGB & sRGB gamma 2.2. That mitigates the impact of gamma changes when converting from RGB to B&W.
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pfigen

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #8 on: February 08, 2017, 03:39:42 AM »

Well, the choice of Gray Gamma in your Color Settings does in fact affect RGB (and CMYK) images in how they display the individual R,G,B,C,M,Y,K plus all three channels in Lab. While this doesn't affect the way your composite RGB/CMYK/Lab is displayed, it has a drastic impact on the channel display, which, depending on what you're doing, might have an effect on what you're doing - using duped channels for any number of reasons, etc.
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kirkt

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #9 on: February 08, 2017, 09:16:09 AM »

The use of false profiles has several applications, but you are essetially reinterpreting what the RGB numbers in your image represent through the use of Photoshop's color management system. The false profile technique can be used in the same color model as the original file to alter the tonal mapping in the image (gamma) or by interpreting RGB numbers originating in one color space with the appearance in another space.  The term "false" profile is used because you are ASSIGNING a color profile to a set of RGB numbers that is not the profile that is the "true" interpretation of those numbers.

The key concept in either case is the the RGB numbers in the file DO NOT CHANGE when you use the false profile technique. The appearance of the image changes, because the RGB numbers are being interpreted differently, but the RGB numbers are preserved.

What are some applications?

Let's say you have an image in AdobeRGB that has weak highlight contrast, maybe due to too much highlight compression or overexposure. There might be little to no clipping in the image, but the highlights are lifeless and need some work. The native gamma for AdobeRGB is 2.2, but you can remap the tones in your image by ASSIGNING a false AdobeRGB profile to the image to tell Photoshop to reinterpret the RGB numbers in a way that uncompresses the highlights and restores the contrast in those areas. You would do this by Assigning a false AdobeRGB profile with a gamma that is greater than 2.2.  This approach will maintain the color (AdobeRGB primaries) but remap the tones. You can then use the darker result to bring the highlights back.  Same goes for images that need shadow and dark midtone lift - you can ASSIGN a false profile that has a lower gamma than the current profile to remap these regions.

A similar approach can be used to enhance or alter color. Let's say you have a drab, dull sRGB image where the colors need some pop. These colors probably live in a narrow region within the sRGB color model close to neutrals. If you ASSIGN a false profile from a larger color space but with a similar gamma, then you reinterpret those color numbers into more colorful versions - you are leveraging the expanded gamut of the larger color space to make things more colorful. So, in this case you may want to ASSIGN a false profile of ProPhoto gamma 2.2 or sRGB gamma to get the color expansion of the larger ProPhoto color space, but with the same or very similar tonal distribution.

Of course you can also modify gamma and color at the same time by assigning a false profile in a different color space with a gamma different than the original file.

In either case, the appearance of the image changes but the RGB numbers do not. To lock in the alteration in tone and/or color, you need to CONVERT the file with the false profile to something else. Photoshop will then alter the RGB numbers so that the appearance in the false profile is maintained in the color space into which you convert.

Here are a couple of articles that describe the concept and some applications:

https://www.ledet.com/margulis/Makeready/MA48-Fate_and_False.pdf

And

http://www.knowhowtransfer.com/the-false-profile-multiply-technique/

Maybe you are referring to the False Profile panel from Giuliana Abbiati.

Kirk
« Last Edit: February 08, 2017, 09:46:12 AM by kirkt »
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Ad_Astra

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #10 on: February 08, 2017, 03:43:25 PM »

The Gray Working Space has no direct impact on RGB images...the Gray Working Space only impacts grayscale images. The only way an RGB image will be modified by the Gray Working Space is when converting from RGB to grayscale.

I set my Gray Working Space gamma to match that of my RGB working space... for PP RGB 1.8 and for ARGB & sRGB gamma 2.2. That mitigates the impact of gamma changes when converting from RGB to B&W.

Hi, I have read that Luminosity masks in Photoshop could get lopsided if the RGB and gray gamma do not match. I have mine matched but wondered if this comment on luminosity masks held true. I would appreciate your thoughts.

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Ad_Astra

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #11 on: February 08, 2017, 03:54:05 PM »

I see the confusion has been cleared up (including the Lr gamma's being unity)
Jim

Hi Jim, I had understood "Melissa RGB" was a gamma 2.2 color space, happy to be corrected but this raises a new question in my mind. Does Lightroom use a gamma of 1.0 for internal calculations and then apply a gamma of 2.2 for display? I would expect the picture to look strange on screen without some kind of tone curve applied.

I also have a longstanding question that I could never figure out.  If Lightroom uses ProphotoRGB color space and different gamma to Photoshop what happens when the raw file is passed to Adobe Photoshop in Prophoto RGB gamma 1.8? I guess as the Lightroom colorspace has a linear gamma there is no shift in tones. I used to think going from a gamma of 2.2 in Lightroom to 1.8 in Photoshop was having a side effect. If I understand correctly there is no side effect as it is really going from gamma 1.0 to gamma 1.8.

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Dave Ellis

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #12 on: February 08, 2017, 04:35:15 PM »

Does Lightroom use a gamma of 1.0 for internal calculations and then apply a gamma of 2.2 for display? I would expect the picture to look strange on screen without some kind of tone curve applied.


This is handled by the Colour management system in place between LR and the display. LR knows what colour space and gamma is in use and it's colour management system modifies this to what the Display ICC profile is "looking for".

Dave
« Last Edit: February 08, 2017, 09:11:53 PM by Dave Ellis »
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Jim Kasson

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #13 on: February 08, 2017, 04:57:55 PM »

Hi Jim, I had understood "Melissa RGB" was a gamma 2.2 color space, happy to be corrected but this raises a new question in my mind. Does Lightroom use a gamma of 1.0 for internal calculations and then apply a gamma of 2.2 for display? I would expect the picture to look strange on screen without some kind of tone curve applied.

Lr uses a unity gamma for its internal representation, with the PPRGB primaries and white point. It converts to your display's color space for display.

One point of potential confusion is Lr's displayed histogram. The horizontal axis on that histogram has a gamma of 2.2, which is applied as the buckets are tallied up.

I also have a longstanding question that I could never figure out.  If Lightroom uses ProphotoRGB color space and different gamma to Photoshop what happens when the raw file is passed to Adobe Photoshop in Prophoto RGB gamma 1.8? I guess as the Lightroom colorspace has a linear gamma there is no shift in tones. I used to think going from a gamma of 2.2 in Lightroom to 1.8 in Photoshop was having a side effect. If I understand correctly there is no side effect as it is really going from gamma 1.0 to gamma 1.8.

Setting aside issues of numerical precision, there no problem converting an image in a color space with gamma G1, primaries R, G, and B and white point W to another color space with the same primaries and a different gamma  say G2.  Boldface indicates vectors or  higher dimension arrays. A computationally inefficient, but easy to follow, way to do that would be, for and image I1 with gamma G1 to an Image I2 with gamma G2, assuming both images have full scale values of one:

unityGammaImage = I1 .^ (G1);
i2 = unityGammaImage .^ (1/G2);

I've used the Matlab notation of .^ to mean taking every element in the images to the exponent.

Thus it's easy for Lr to convert its internal color space to real PPRGB to export an image to Ps.

Jim
« Last Edit: February 08, 2017, 05:01:50 PM by Jim Kasson »
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Ad_Astra

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #14 on: February 09, 2017, 05:37:38 PM »

Thanks Jim for explaining the gamma conversion. I can stop worrying about the gamma changes from LR to Photoshop.

I am still a little puzzled by the unity gamma in LR. E.g. I thought the highlights slider was effectively moving the curved / flattened area of the gamma curve so that you recovered detail in the highlights by moving to the stepper part of the gamma curve. If LR has a unity gamma how does the highlight slider work behind the scenes?



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Jim Kasson

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #15 on: February 09, 2017, 06:07:37 PM »

Thanks Jim for explaining the gamma conversion. I can stop worrying about the gamma changes from LR to Photoshop.

I am still a little puzzled by the unity gamma in LR. E.g. I thought the highlights slider was effectively moving the curved / flattened area of the gamma curve so that you recovered detail in the highlights by moving to the stepper part of the gamma curve. If LR has a unity gamma how does the highlight slider work behind the scenes?

The reason for the unity gamma in Lr is to make the computations less computationally expensive; operations that blend the way that light blends are naturally implemented in linear spaces, and the order of operations tens to be less important. The "curves" shown in Lr are with a non-linear horizontal axis like the horizontal axis in the histogram. The curves that you see are for illustration. The curves that are applied in gamma = 1 space are not shaped like that, but are shaped as if the non-linear horizontal axis had been transformed with the same kind of exponential transform required to convert between color spaces of different gammas. However, that transform is computationally cheap, since the curve is one-dimensional, while the images are three dimensional.

Jim

scyth

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #16 on: February 09, 2017, 07:23:58 PM »

I guess as the Lightroom colorspace
LR is using many different colorspaces (cieXYZ, cieLAB, PP/g1, etc) in its pipeline when it renders the "image" from raw file to display/print/export/whatever... there is no single one ...
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Simon Garrett

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #17 on: February 10, 2017, 06:39:48 AM »

LR is using many different colorspaces (cieXYZ, cieLAB, PP/g1, etc) in its pipeline when it renders the "image" from raw file to display/print/export/whatever... there is no single one ...

Quite so. To list a few colour spaces LR uses:
  • Develop Module: ProPhoto RGB with linear gamma for computation
  • Library Module: Adobe RGB (images stored in previews in this form)
  • Histogram and curves in Develop: ProPhoto RGB but 2.2 gamma (more accurately: sRGB's gamma)
  • Histogram in Library: I assume (not sure) it uses Adobe RGB from the preview
  • Web Module: sRGB
And of course one can soft-proof, getting an emulation of what the image might look like if converted to the emulated colour space (and then colour-managed to the monitor's colour space).
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scyth

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #18 on: February 10, 2017, 09:14:39 AM »


  • Develop Module: ProPhoto RGB with linear gamma for computation


it uses a lot more of colorspaces in "Develop Module" in addition to "ProPhoto RGB with linear gamma" - see the posting above
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Simon Garrett

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Re: New Photoshop CC 2017 gamma options - which to use with Lightroom?
« Reply #19 on: February 10, 2017, 03:27:58 PM »

it uses a lot more of colorspaces in "Develop Module" in addition to "ProPhoto RGB with linear gamma" - see the posting above

My list was in addition to yours.  As you say, conversions are likely to go via one of the Profile Connection Spaces during any conversion, LR's colour management will also use the monitor's colour space, perhaps a printer's colour space, any proofing colour space, any export colour space...  Such is the case with a colour managed system. 
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