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askap-vast / vast-post-processing

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Finalise compression quantisation #80

Closed ddobie closed 5 months ago

ddobie commented 7 months ago

We currently use a "quantize_level" of 1024, which means that scaled integer pixel values will be quantized such that the difference between adjacent integer values will be 1/1024th of the noise level in the image background as calculated by astropy. The default level used in astropy is 16.

For reference, I achieve the following file sizes after cropping SB51490 to the central 6.3 deg square and applying compression

Quantise level File size (MB)
8 67.3
16 77.5
64 98.1
128 109
256 119
512 129
1024 139
taramurphy commented 7 months ago

How big was SB51490 originally? What if you do cropping but no scaling?

ddobie commented 7 months ago

The raw image is 720MB (typically our images are 700-750MB). Cropping to a 6.3 degree square without any compression reduces it to ~310MB