Why are .HDR files so much smaller than the rest?

[Victor Lin]

I've got a 171MP 360-degree pano. 

32-bit TIF, PSD, PSB, and EXR with no compression all hover around 1.9 GB (TIF with LZW and PackBits compression are actually larger, for some reason).

32-bit EXR with PIZ compression is 1.32 GB.

But saving as an .HDR file yields a file size of only 0.652 GB.

What's going on here? Surely .HDR files are 32-bits? Is there a lot of lossy compression going on?

[PTGui Support]

Hi Victor,

Yes, they are lossy compressed. In particular, you may see banding
artifacts near saturated colors.

Kind regards,

Joost Nieuwenhuijse
www.ptgui.com

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