1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2
3 .. _v4l2-pix-fmt-pisp-comp1-rggb:
4 .. _v4l2-pix-fmt-pisp-comp1-grbg:
5 .. _v4l2-pix-fmt-pisp-comp1-gbrg:
6 .. _v4l2-pix-fmt-pisp-comp1-bggr:
7 .. _v4l2-pix-fmt-pisp-comp1-mono:
8 .. _v4l2-pix-fmt-pisp-comp2-rggb:
9 .. _v4l2-pix-fmt-pisp-comp2-grbg:
10 .. _v4l2-pix-fmt-pisp-comp2-gbrg:
11 .. _v4l2-pix-fmt-pisp-comp2-bggr:
12 .. _v4l2-pix-fmt-pisp-comp2-mono:
13
14 **************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************
15 V4L2_PIX_FMT_PISP_COMP1_RGGB ('PC1R'), V4L2_PIX_FMT_PISP_COMP1_GRBG ('PC1G'), V4L2_PIX_FMT_PISP_COMP1_GBRG ('PC1g'), V4L2_PIX_FMT_PISP_COMP1_BGGR ('PC1B), V4L2_PIX_FMT_PISP_COMP1_MONO ('PC1M'), V4L2_PIX_FMT_PISP_COMP2_RGGB ('PC2R'), V4L2_PIX_FMT_PISP_COMP2_GRBG ('PC2G'), V4L2_PIX_FMT_PISP_COMP2_GBRG ('PC2g'), V4L2_PIX_FMT_PISP_COMP2_BGGR ('PC2B), V4L2_PIX_FMT_PISP_COMP2_MONO ('PC2M')
16 **************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************
17
18 ================================================
19 Raspberry Pi PiSP compressed 8-bit Bayer formats
20 ================================================
21
22 Description
23 ===========
24
25 The Raspberry Pi ISP (PiSP) uses a family of three fixed-rate compressed Bayer
26 formats. A black-level offset may be subtracted to improve compression
27 efficiency; the nominal black level and amount of offset must be signalled out
28 of band. Each scanline is padded to a multiple of 8 pixels wide, and each block
29 of 8 horizontally-contiguous pixels is coded using 8 bytes.
30
31 Mode 1 uses a quantization and delta-based coding scheme which preserves up to
32 12 significant bits. Mode 2 is a simple sqrt-like companding scheme with 6 PWL
33 chords, preserving up to 12 significant bits. Mode 3 combines both companding
34 (with 4 chords) and the delta scheme, preserving up to 14 significant bits.
35
36 The remainder of this description applies to Modes 1 and 3.
37
38 Each block of 8 pixels is separated into even and odd phases of 4 pixels,
39 coded independently by 32-bit words at successive locations in memory.
40 The two LS bits of each 32-bit word give its "quantization mode".
41
42 In quantization mode 0, the lowest 321 quantization levels are multiples of
43 FSD/4096 and the remaining levels are successive multiples of FSD/2048.
44 Quantization modes 1 and 2 use linear quantization with step sizes of
45 FSD/1024 and FSD/512 respectively. Each of the four pixels is quantized
46 independently, with rounding to the nearest level.
47 In quantization mode 2 where the middle two samples have quantized values
48 (q1,q2) both in the range [384..511], they are coded using 9 bits for q1
49 followed by 7 bits for (q2 & 127). Otherwise, for quantization modes
50 0, 1 and 2: a 9-bit field encodes MIN(q1,q2) which must be in the range
51 [0..511] and a 7-bit field encodes (q2-q1+64) which must be in [0..127].
52
53 Each of the outer samples (q0,q3) is encoded using a 7-bit field based
54 on its inner neighbour q1 or q2. In quantization mode 2 where the inner
55 sample has a quantized value in the range [448..511], the field value is
56 (q0-384). Otherwise for quantization modes 0, 1 and 2: The outer sample
57 is encoded as (q0-MAX(0,q1-64)). q3 is likewise coded based on q2.
58 Each of these values must be in the range [0..127]. All these fields
59 of 2, 9, 7, 7, 7 bits respectively are packed in little-endian order
60 to give a 32-bit word with LE byte order.
61
62 Quantization mode 3 has a "7.5-bit" escape, used when none of the above
63 encodings will fit. Each pixel value is quantized to the nearest of 176
64 levels, where the lowest 95 levels are multiples of FSD/256 and the
65 remaining levels are multiples of FSD/128 (level 175 represents values
66 very close to FSD and may require saturating arithmetic to decode).
67
68 Each pair of quantized pixels (q0,q1) or (q2,q3) is jointly coded
69 by a 15-bit field: 2816*(q0>>4) + 16*q1 + (q0&15).
70 Three fields of 2, 15, 15 bits are packed in LE order {15,15,2}.
71
72 An implementation of a software decoder of compressed formats is available
73 in `Raspberry Pi camera applications code base
74 <https://github.com/raspberrypi/rpicam-apps/blob/main/image/dng.cpp>`_.
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