Author Topic: How do I measure sRGB values in photoshop? (From Allegorithmic PBR Guides)  (Read 6835 times)

Good evening.

I've been reading the PBR Guides and in Vol2 it gives you guideline values for diffuse colors.
"For bright colors, you
should not have any values that go above 240 sRGB"

How do I check what values my colors/textures are in Photoshop? I'm trying to get some good green values for leaves that will work in a PBR workflow.

Thank you.

You can check with the levels (ctrl +L)

Hi Vince.

Thanks for the reply

How does the levels command give a numeric reading?
I need a numeric reading. The Levels command only shows the graph.

Ok It looks like the Info Pallete in Photoshop will give you exact RGB read outs wherever you hover over your mouse on your image.

One thing I don't understand though is the guidelines in the PBR Guide book only give you ONE number for a guide. Example: No darks should go below 50 srgb. I assume they mean that no value in any of your 3 RGB channels should go below 50?


Yes, no dark in general... Try also the curve tool (ctrl +m)

Hey tellychris,

as far as I know there is no such an option in photoshop, but I would use a workaround for this.
Create a Levels adjustment layer and select the mask (rectangle next to the levels adjustment).

What I would do then is to go to 'Select -> Colour Range'.
- Set Fuzziness to 0%
- Range: Your desired range. In my example: All values below an sRGB value of 30 (Screenshot attached)

(Yes, Vincent is right, in the Guide when talked about 30-50 sRGB it is meant to use Red 30, Blue 30, Green 30)

This way you see if you have any values fitting in your range.
If you click on OK now, this selection is used as a mask inside the levels node. Now you can edit the Output Levels and all values should be lifted.

You also could do the levels node without having to select the colour range, but to see those values this trick is quite useful and you also could use this as a mask for anything. You also could use it to check if your levels work correctly.


Best Reagrds
Last Edit: March 23, 2015, 08:02:11 am
Environment Artist - Twitter

You can even make an action to automate the process :auto levels then set the low and high to the proper values.

That said it's feasible in SD as well, I am pretty sure.

i am not sure if this will match the question , but you can in photoshop to convert rgb to srgb without to touch the color profile, you can just  do this :

Image > adjustments> color Balance



it will transforms the RGB value into what should be the Srgb values when converted to the proper color profile.
but the file remains to be in RGB profile, so it could only be used to check the final result, but nothing you can really use for production.

Just to clarify. Using the Info pallete near the histogram will NOT give me accurate values when I hover over a pixel?

In my picture it shows my green is in the 50-240 range. It's showing 123 in the info pallete. Does that not mean I am in the acceptable range if I wanted to use this green for a leaf color?

Please see attached. Thanks for the help.

Hey tellychris,

the Info Panel gives you exact values. You can use it, of course. :)


Best regards
Environment Artist - Twitter

Once again, you don't need to do it "by channel" : you can do both channel at the same time.
To get a view you can use the histogram (see first image)

And to fix the levels fastly, use the level tools (see second image):
First you make an autolevel
then you setup the output levels.

it should work in most of the cases (except if you havebig "holes" in your histogram

One thing I don't understand though is the guidelines in the PBR Guide book only give you ONE number for a guide. Example: No darks should go below 50 srgb. I assume they mean that no value in any of your 3 RGB channels should go below 50?

Hello, sorry for digging out an old thread, but as this is in the learning category, and people will still be using these topics for reference (like I was just now), I think this is important.

Let's assume we're using the strict rule (min 50 sRGB).

I tested it in Designer, using the "PBR Albedo Safe Color", "PBR BaseColor / Metallic Validate" and "Uniform Color" nodes (plus additional Uniform Color node to test stuff with the color picker).

When you start with dark green color (0,52,0), Validate gives thumbs down (it's too dark), and Safe Color converts it to (48,52,48). Grey, which is obviously not what we wanted.

But, if you start moving the Value slider up in Uniform Color (HSV mode), at 88 Validate gives full thumbs up. Which is simply (0,88,0). Still green color, which is what we wanted. This shows that individual channels can be below 50 (even 0), and still satisfy the restrictions.

Which makes sense, because if you convert a (0,88,0) color to black & white for example in Photoshop, it gives a (51,51,51) value, which is in the safe range. This would suggest that it's the overall value (greyscale value) that matters, not individual channels.

HOWEVER (and I wonder if this is a bug), I noticed something weird: for the "PBR BaseColor / Metallic Validate" node, (0,88,0) is OK, but (88,0,0) and (0,0,88) are not. In fact, for red, (175,0,0) seems to be the minimum, and for blue even (0,0,255) is not accepted... Is this by design, resulting from some real-life properties of colored materials, or simply a bug?

One thing I don't understand though is the guidelines in the PBR Guide book only give you ONE number for a guide. Example: No darks should go below 50 srgb. I assume they mean that no value in any of your 3 RGB channels should go below 50?

Hello, sorry for digging out an old thread, but as this is in the learning category, and people will still be using these topics for reference (like I was just now), I think this is important.

Let's assume we're using the strict rule (min 50 sRGB).

I tested it in Designer, using the "PBR Albedo Safe Color", "PBR BaseColor / Metallic Validate" and "Uniform Color" nodes (plus additional Uniform Color node to test stuff with the color picker).

When you start with dark green color (0,52,0), Validate gives thumbs down (it's too dark), and Safe Color converts it to (48,52,48). Grey, which is obviously not what we wanted.

But, if you start moving the Value slider up in Uniform Color (HSV mode), at 88 Validate gives full thumbs up. Which is simply (0,88,0). Still green color, which is what we wanted. This shows that individual channels can be below 50 (even 0), and still satisfy the restrictions.

Which makes sense, because if you convert a (0,88,0) color to black & white for example in Photoshop, it gives a (51,51,51) value, which is in the safe range. This would suggest that it's the overall value (greyscale value) that matters, not individual channels.

HOWEVER (and I wonder if this is a bug), I noticed something weird: for the "PBR BaseColor / Metallic Validate" node, (0,88,0) is OK, but (88,0,0) and (0,0,88) are not. In fact, for red, (175,0,0) seems to be the minimum, and for blue even (0,0,255) is not accepted... Is this by design, resulting from some real-life properties of colored materials, or simply a bug?

Hi,

I don't think it's a bug. (88,0,0) reads at ok for Albedo at the 30 srgb range. These are just approximations. The node wasn't designed to be used with a single uniform color. For (0,0,255) I get the green result. Are you using the albedo or metal mode? For metal, this would show incorrect.

Cheers,

Wes
Integrations Product Manager / Training
wes.mcdermott@allegorithmic.com
Twitter: The3DNinja

Still, it doesn't make much sense when it works for one color, and doesn't for another. Unless there's some physically-based explanation behind it.

Especially when you think of the colors not in terms of RGB, and some channels being 0, but in terms of hue. Set color to RGB(0,88,0), switch to HSV and move the Hue slider. Repeat for (0,0,255).

I'm using Albedo mode, and the strict 50 sRGB threshold, like I said in the previous post.