I was experimenting with heightmap and I discovered that Blender cannot invert the image file in a way that is absolutely negative version of the original image. So I started reading and found out that Blender has a linear color space that makes this difference. If I invert the image with Photoshop, I get very much different version of the image.
First, the image inverted with Blender. The original image is also visible in Blender picture
And the Photoshop version.
Now, when I save the file in Blender to PNG and then open it again in Blender without progression and try to invert it to the original, I get (slightly) different version of the image (Only small difference visible). However I don’t know if it’s because of blender’s PNG exporter, but still there is some difference. In Photoshop I can do this operation without any difference between the files.
In the center there is the original PNG heightmap that can be downloaded from this link: https://dl.dropboxusercontent.com/u/5904620/Blender_aid/mosaic.png .
Left is the photoshop version of inverted and saved PNG heightmap. Right there is the map inverted in Blender and saved to PNG.
Of course I cannot use the heightmap that is inverted in Blender, because the result is just wrong. I can indeed invert it in displace modifier and get correct displacement, but if I need for some reason the corrected version of the height map, I don’t know how to get it with Blender.