Yes. If your build of Dolphin was compiled with ffmpeg support (this is the case if it is able to create AVI files), then set the following in GFX.ini to get it to output PNG instead:
[Settings]
DumpFramesAsImages = True
However, if you want to grab just a few frames for comparison, it may be easier to just use Dolphin's screenshot functionality. It uses the same code.
[Settings]
DumpFramesAsImages = True
However, if you want to grab just a few frames for comparison, it may be easier to just use Dolphin's screenshot functionality. It uses the same code.