Operating system: Windows 10 Pro 10.0.17134 Build 17134
Graphics card: Nvidia 660 GTX
Broken: 2.80 (sub 35), branch: blender2.8, commit date: 2018-11-30 00:46, hash: 4c31bed6b46, type: Release
Previous versions (2.79 and earlier) are broken too in similar ways.
Short description of error
Some float TIFF files get rendered in wrong colors in eevee or cycles. Even though the image looks correct in the image viewer, it will show wrong colors in the render. But i mainly tested normal maps, so the report will be about normal maps.
Here are some example outputs which compare the original float TIFF image with a version externally converted to integer. The image is applied as normal map, both versions of the normal map look the same in any external program or even the blender image viewer, but they render differently. Left uses the original image and right uses the converted image:
|Rendered in eevee|
|Rendered in cycles, but files are not packed into the blend file|
|Rendered in cycles, but files are packed into the blend file|
I'm not sure yet, but it seems it doesn't happen with all float RGB TIFF images. I could only reproduce it with normal maps i have here. Some float RGB TIFF images for the base color didn't show any huge color differences in the output.
Exact steps for others to reproduce the error
Here is a blend file from which the above examples where created from. For some reason it makes a difference for cycles if the images are packed into the blend file, so you may unpack or repack the two textures to test. To reproduce the behaviour, just open the file in blender 2.8 and display the viewport as LookDev or Rendered.