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Weird gamma using spot light with bitmap
Posted: Thu Oct 18, 2018 1:05 pm
by davorin
Good afternoon (o;
I am doing some simulation of user interfaces where a spot light with a bitmap cast an image onto a semitransparent glass object...
Suddenly I discovered when I used color gradients in the bitmap that the gamma is totally wrong in rendering...looks like brightness over saturation...
Original bitmap:
- linear_gradient.png (9.91 KiB) Viewed 3638 times
and rendered output (bitmap is turned 180 degrees):
Also it depends from which side the camera is looking onto....
Re: Weird gamm using spot light with bitmap
Posted: Thu Oct 18, 2018 1:15 pm
by B.Y.O.B.
Have you specified the correct gamma value for the image?
How do your color management settings look like, are you using filmic?
Can you upload a testscene with all textures that shows the problem?
Re: Weird gamm using spot light with bitmap
Posted: Thu Oct 18, 2018 1:27 pm
by davorin
Tried a little with gamma settings...but higher values gets me more of the left side being dark...
color settings I didn't touch as other stuff looks normal to me...
Attached the scene...think it should contain all bitmaps..
BTW: What is best for a spot light bitmap?
Using a black background or using a transparent background?
Re: Weird gamma using spot light with bitmap
Posted: Thu Oct 18, 2018 1:39 pm
by davorin
This is now with a higher gamma value for the bitmap (5):
Note the fine line at the left which should be not lit...
Especially the effect can be seen with this bitmap I used originally.
The gradients around the white circles are almost flat:
Re: Weird gamma using spot light with bitmap
Posted: Thu Oct 18, 2018 1:54 pm
by B.Y.O.B.
You are using filmic color management.
Your image is probably completely over-exposed. Filmic has this behaviour that overexposed colors get desaturated instead of blowing out.
Also, the gamma of your image is probably 2.2, not 5, which leads to excessive banding because the 8 bit image does not have enough information.
Attached is a fixed scene where these problems are solved.
Re: Weird gamma using spot light with bitmap
Posted: Thu Oct 18, 2018 2:00 pm
by davorin
Wow..that looks great...think I have to adjust the other lamps as the cube below is now too dark (o;
many thanks
richard
Re: Weird gamma using spot light with bitmap
Posted: Thu Oct 18, 2018 2:06 pm
by B.Y.O.B.
Or you have to make the overall image brighter by adjusting the tonemapper scale, but in turn make the spot light darker.
By the way, I disabled automatic tonemapping, this is usally better once you know the tonemapping scale your scene needs.
And one general tip: if you use filmic, sometimes switch to default to make sure your image is not completely over-exposed.