I'm trying to convert NEF files to PNG or some other lossless format.

Using Preview/Imagemagick, the 10MB NEF file is converted to 60-70MB png file or 95MB tiff file.

Also tried converting to HEIC but it only allows 8bit depth, the resulting files are relatively small, 7MB.

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    TIFFs are always a lot bigger than NEFs. Mine go from 30MB to 140. I've no real idea why PNGs should be larger. – Tetsujin Nov 5 '20 at 10:19
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    What is your final goal that requires that you save the NEF file into another format? Archive? Display on the web? – Saaru Lindestøkke Nov 5 '20 at 11:14
  • Move to phone gallery – Avner Barr Nov 5 '20 at 12:02
  • Why do you need 16bit PNG on your phone? – xiota Nov 5 '20 at 14:04
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    This is not a complete answer - we'd need more information on the exact formats - but a couple factors would be that the NEF is 12- or 14-bits per pixel, and only a single value at each sensor site. Going to 16-bit is a 14-33% change per value. Then, the PNG/TIFF have three values per pixel (RGB), so that's an additional 3X expansion. Then there's the difference in compression algorithms - not sure exactly what NEF uses, but PNG and TIFF have several options, including uncompressed.... – twalberg Nov 5 '20 at 14:27

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