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nevcairiel · 21st March 2018, 23:23

There is actually a bit of a trick when extending the bitdepth of a full range signal, you fill the new bits with the leading bits of the pixel, ie. like this for 8 to 10-bit:

- You shift to 10-bit first, which adds two empty bits.
- Then you fill those empty bits with the top bits from the original signal

Code:

  1111111100
+         11111111
= 1111111111

This has several good properties, namely:
- All 1 also remains all 1, ie. maximum 8-bit (255) remains maximum 10-bit (1023)
- Zero also remains zero
- Its easy and fast

I can't say that this is what its doing, but it is generally regarded as producing a more faithful signal when increasing bitdepth then plain zero padding, and a full stretch from 0-255 to 0-1023 is computationally rather expensive.

Note that this does not apply when you are dealing with limited range (ie. 16-235), because 16 and 235 map to the limited-range 10-bit values exactly when you simply shift them up (ie. 64 to 940)
But when handling full-range signals like RGB, plain zero padding is not entirely accurate.

21st March 2018, 23:23	#49748 \| Link
nevcairiel Registered Developer Join Date: Mar 2010 Location: Hamburg/Germany Posts: 10,348	There is actually a bit of a trick when extending the bitdepth of a full range signal, you fill the new bits with the leading bits of the pixel, ie. like this for 8 to 10-bit: - You shift to 10-bit first, which adds two empty bits. - Then you fill those empty bits with the top bits from the original signal Code: 1111111100 + 11111111 = 1111111111 This has several good properties, namely: - All 1 also remains all 1, ie. maximum 8-bit (255) remains maximum 10-bit (1023) - Zero also remains zero - Its easy and fast I can't say that this is what its doing, but it is generally regarded as producing a more faithful signal when increasing bitdepth then plain zero padding, and a full stretch from 0-255 to 0-1023 is computationally rather expensive. Note that this does not apply when you are dealing with limited range (ie. 16-235), because 16 and 235 map to the limited-range 10-bit values exactly when you simply shift them up (ie. 64 to 940) But when handling full-range signals like RGB, plain zero padding is not entirely accurate. __________________ LAV Filters - open source ffmpeg based media splitter and decoders Last edited by nevcairiel; 21st March 2018 at 23:32.