Timeline for Why shouldn't Bump, Normal and Displacement maps be gamma corrected?
Current License: CC BY-SA 3.0
11 events
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| Aug 15, 2016 at 3:09 | comment | added | user1118321 | This answer is factually incorrect. You tell Photoshop in what color space to manipulate data, and many images have information about what colorspace they are stored in. Photoshop will convert from the image's color space to its working space (which you can change), and can save color space info in the images it creates. If there is no color space info stored in the image, it makes a decision about which color space it assumes. But it is always doing this unless you specifically set it not to, and that is not the default. | |
| Aug 12, 2016 at 12:07 | comment | added | Quinchilion | You got it. The gradient will only look linear on the screen if you apply gamma correction to it. That, however, makes the gradient itself non-linear in terms of the raw values and thus unsuitable for use as a displacement map. | |
| Aug 12, 2016 at 9:58 | comment | added | Kristoffer Helander | If I create a gradient, let say 256 pixels wide, and I make sure those pixels are linear going from 0, 1, 2, 3, ... to 255. Then I have created a linear ramp, and if I use that as a displacement in 3D without any gamma correction in the 3D software I get a linear displacement effect. But does that same gradient look linear on the screen? And if I wanted to use that same gradient as a diffuse texture, I would have to apply the gamma correction on it, right? So when piping the map into Displacement you keep the pixels as is, but for Diffuse you have to linearize the texture by gamma correcting? | |
| Aug 11, 2016 at 16:11 | comment | added | Quinchilion | @KristofferHelander It's a confusing subject, I understand. As I was trying to say, Photoshop does no conversions. So if you load an image that is stored with gamma, it stays with gamma applied and because of that blurring is wrong. If you load a displacement map that is treated as linear data, it is loaded as linear and saved as linear because no conversions are applied by Photoshop by default. There is no special treatment based on the color model. The only difference between the two is that the displacement map is displayed wrong - the display still applies a gamma of 2.2 to it. | |
| Aug 11, 2016 at 14:19 | comment | added | Kristoffer Helander | If I fill a document in Photoshop half side red (255,0,0) and the other half with green (0,255,0) and then use a Gaussian blur on that, the resulting gradient becomes brownish rather then yellow in the middle as shown in that video I posted. Why is that? If the pixels in the image are linear then why does the math get screwed up? I don't understand how a displacement map painted in Photoshop is linear and good to go for rendering but at the same time the blurring of pixels gets screwed up with the wrong gamma and colors become to dark and brownish? | |
| Aug 11, 2016 at 13:58 | comment | added | Quinchilion | @KristofferHelander goo.gl/yqkeUP The bottom gradient represents physical brightness. If Photoshop applied a gamma of 1/2.2 for either drawing the gradient or displaying the image, you would see the bottom gradient. Instead, you see the top one, which coincidentally appears to be linear, but isn't. It also wouldn't work for viewing photos. The camera applied 1/2.2 when saving the photo, then Photoshop would apply another 1/2.2, but the display only adds gamma of 2.2 once. That wouldn't look right. | |
| Aug 11, 2016 at 13:31 | comment | added | Kristoffer Helander | Correct me if I'm wrong on this. When I draw a gradient ramp in Photoshop that looks linear to me on the screen the values in that ramp actually are linear. But Photoshop adds a viewing gamma of 1/2.2 since the monitor adds a gamma of 2.2, thus the images pixel values are linear and they also look linear. But this 1/2.2 gamma is only a viewing gamma that Photoshop use for displaying the image, it is not baked into to image, and therefore no gamma correction to the image need to be done in the 3D software, (use gamma 1.0) since the values already are linear? | |
| Aug 10, 2016 at 15:33 | comment | added | Quinchilion | @KristofferHelander Yes, but he says it's only the camera that stores the values as square roots and only the display that squares it back. Image editing software like Photoshop then just open and save the image with no conversions, which results in artifacts shown in the video when you try to blend colors. | |
| Aug 10, 2016 at 15:22 | comment | added | Kristoffer Helander | Here is a YouTube video also explaining that the stored value in an image is the 1/2.2 (but he simplifies it and just say that it's the square root, there is a disclaimer of that in text.) Computer Color is Broken - MinutePhysics link | |
| Aug 10, 2016 at 15:15 | review | First posts | |||
| Aug 20, 2016 at 2:10 | |||||
| Aug 10, 2016 at 15:14 | history | answered | Quinchilion | CC BY-SA 3.0 |