It's weird because now I'm finding that for my base color textures, the TGA looks too saturated in UE4, and the PNG looks too washed out. SRGB is checked for the base color texture of each in UE4.
There is a bug in UE4 regarding the import of 16bit PNG, they have a wrong sRGB correction. If you force your PNG to 8bits, it should fix the issue. The Targa format doesn't have the issue.
IIRC ue4 doesn't support 16bit textures (for materials) and the engine converts them to 8bit. I remember seeing some people with problems with washed out textures in ue4 with the sRGB check box not doing what it was supposed to. As for the TGA looking dull and oversaturated it might be that the sRGB property isn't checked…
Correct. The 16-bits per channel image has no gamma curve (tonemapping) applied to it. 8-bit images are stored with a gamma curve is applied. This is back when photographs first became digital, in order to represent on a computer screen what you see in real life (because a lack of bit-depth in displays) it was found that…