Blender saves to different formats using different techniques and curving according to some file based assumptions. TIFFs do not save "raw" by default, nor does the term "raw" have any real meaning here. Some examples file formats may have on output include:
- Saving to a JPEG or TIFF at 8 bits per channel will apply a nonlinear sRGB curve to the data, and may change the internal float format to the respective format's storage type.
- Saving to an EXR will transfer the internal reference space buffers unchanged which, by nature of EXR, is a linearized float scene referred format.
From what I can deduce from your screenshot(?) it appears that a subtle shifting is happening in the intensity along the trunk. This suggests that the right image is being color managed for your display from within Photoshop.
Blender does not use ICCs for color management, nor is the display corrected by default. Further, it will not tag images with ICC profile information when saving. This means that the software will make a guess as to what reference space the image is in when it is loaded.
If I had to speculate, I would guess that the image viewer on the right is color correcting the assumed sRGB image format you have loaded. This effectively takes the theoretical sRGB values output from Blender and attempts to emulate the correct sRGB values based on a profile of your display. It may also have to do with an incorrect reference space being set from within your image viewer.
So without further information, it would be impossible to diagnose what is happening with absolute certainty. That said, if you open the color management settings in Photoshop, you will likely find a display correction profile in place there, or an incorrect working reference space ICC profile. In the case of the former, you can disable the display profile and see the raw dump to the screen as Blender rendered it. In the case of the latter, there are sadly many sRGB ICC profiles out there that are not identical to each other, and some are even outright incorrect.
Hope this helps you make a little progress into figuring out the issue.
- Blender can be augmented to display color critical and accurate results, hardware depending. This involves profiling one's display, converting the resulting profile into a 3D LUT, and inserting it into the OpenColorIO configuration set.
- The sRGB.icm ICC file included with the Argyll color management system is accurate and should deliver proper output.