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13thsymphony / HDRImageViewer

UWP app to view high dynamic range (HDR) and wide color gamut (WCG) images.
https://13thsymphony.github.io/
MIT License
76 stars 21 forks source link

Estimated MaxCLL changes based on window size #53

Open Sawtaytoes opened 1 year ago

Sawtaytoes commented 1 year ago

Thanks for making this great piece of software! I use it all the time to help figure out what's going on in HDR space.

For some reason, the Estimated MaxCLL calculation changes pretty drastically based on the window size. I've noticed it report 300 nits darker if the window is smaller in images that are 600 nits peak.

Is this because it composites the current frame and grabs the brightest pixel rather than looking at the full-res image?

13thsymphony commented 1 year ago

Sorry for the delay in responding.

Unfortunately, I don't have an explanation for your reported behavior. The MaxCLL calculation DOES do a downscale, but this is based on the source/image's dimensions and is intended to bound the cost of the calculation for very large image sizes. Right now it caps the larger image dimension to the lesser of 0.5 and 2048 pixels.

The window size handler explicitly is supposed to not recalculate MaxCLL.

Do you mind sharing more repro info - is there a particular image that shows the change, certain specific window pixel sizes that trigger this (even a guestimate), also your GPU, driver and display info (a dxdiag would be sufficient).

Thanks!