Default image extension

[beersandrew]

Nick Porcino mentioned about having a default file format of exr since he can color manage exr and not png.

@hybridherbst wanted to discuss.

creating this issue for a discussion about the pros and cons of different default extensions

[meshula]

jpeg, png, and exr are built into UsdImaging and always available to Hydra as of 23.11. As of 23.08 OpenEXR is only available via the OIIO plugin. EXR is always available to usdz, as of 23.08.

8 bit imagery saves space. exr is the HDR format of choice.

jpeg

lossy
good compression
srgb, 8 bit
no alpha channel

png

lossless
moderate compression (LZ77)
linear or srgb, 8 or 16 bits
alpha channel (un-premultiplied)

exr

lossless
moderate compression (LZ77, dwa a and b)
linear, 16 or 32 bits
color space specified as chromaticities plus white point
alpha (un-premultiplied)
rich attribute system including camera matrices, SMPTE 2065 attributes, and camdkit

exr features not yet exposed to usd, but expected in the future

depth (z) images
deep pixels (multiple samples per pixel, depth information)
unlimited layers (diffuse, specular, etc)
unlimited parts (frame 0, frame 1, etc)