Help with the Equation for converting Gamma to Linear.

synergy11

Good day.

0.5^(1 / 2.2) = ~0.73 * 255 = 186

This is the equation for getting a linear space value (0.5) converted to a gamma space rgb value (186)

I am having trouble doing the opposite. What I want to do is convert a RGB value in Gamma space into a 0-1 linear value
Does anyone know what the formula is?

Thanks in advance.

Cheers.

Pikamus

Linear to Gamma

255*POWER(linearvalue/255,1/2.2)

Gamma To Linear

255 * POWER(gammavalue / 255,2.2)

monster

(186.0/255.0)^2.2 = 0.499505

RN

Note that 'linear' in this sense is that a certain 'x' value is mapped to the same 'y' value. It means it forms a "straight line graph."

That 'linear' has no relation to the data type used to represent the colour value -- whether it's represented by a normalised floating point value (0.0 ~ 1.0) or by an unsigned byte value (0 ~ 255).

Both of these data types can be used to represent both the linear-space and gamma-space RGB values. So you're dealing with two operations: how to convert back-and-forth between data types ( float <---> byte ) and how to convert back-and-forth between RGB spaces ( linear <---> gamma ).

EDIT: This all means that you don't need to convert to the byte range (i.e. multiply by 255) if you only need the result to be in floating point.

synergy11

Thanks Monster.

All I want to be able to do is get my color choices matching from Photoshop to Unreal engine 4 materials (RGB to 0-1). Also If I find a nice roughness value in Unreal I want to be able to paint that as my base roughness texture map in Photoshop. (0-1 to RGB)

Kryzon: I have no idea what you just said. HAH! I wish I did though.

On second thought Kryzon. That is what I am trying to do. First I need to convert the values from byte (0-255) to float value (0-1) then I need to convert RGB spaces (gamma to linear), I just did not have the proper language. Thanks!

As a side note: Does anyone know of a online converter/calculator that will convert anyRGB value in Photoshop into a Float value and also convert the RGB spaces?

Thanks again!

RN

In that case, Photoshop can display colours in a different way than Unreal depending on your Colour Management settings.

What you can do is go to Edit -> Colour Settings, and in "Working Spaces," select the "Monitor RGB" option in the RGB field. This turns off the Photoshop colour management and the colours that you pick now should look the same in Unreal.

Now you can click on the colour squares (in the toolbar) to open the extended colour picker, and you can see there the hex code for the currently picked colour. While the picker window is open you can also pick from your layers, you just have to click on the pixels.
Then you can copy the hex value and use it with something like this to get the float version:
http://www.corecoding.com/utilities/rgb-or-hex-to-float.php

EDIT: I think Unreal 4 already does gamma correction internally for you, so you shouldn't have to worry about it.
In any case, this article should explain more. It seems to be a texture property that you set in Unreal:
http://artbyplunkett.com/Unreal/unrealgamma.html#_Toc268114684

Count Vertsalot

https://maddieman.wordpress.com/2009/06/23/gamma-correction-and-linear-colour-space-simplified/

That might be helpful.

Xom01

A long time ago of your question and maybe you already solved it. but for those who still do not know it in photoshop there is a way to convert values from gamma 1 to gamma 2.2 or vice versa. With the color picker and with an exposure adjustment layer feeding the gamma correction either 0.4546 or 2.2 depending on the case if you want to convert from gamma 2.2 to gamma 1.0 or from gamma 1.0 to gamma 2.2 in the information box will launch you the equivalent values for the two gammas.

kanikama

thank you very much @Xom01 it works perfecly except in layers with transparency, I'm pretty much sure that there should be a good reason, but for me it is a bit from Photoshop side