1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _v4l2-pix-fmt-pisp-comp1-rggb: 5.. _v4l2-pix-fmt-pisp-comp1-grbg: 6.. _v4l2-pix-fmt-pisp-comp1-gbrg: 7.. _v4l2-pix-fmt-pisp-comp1-bggr: 8.. _v4l2-pix-fmt-pisp-comp1-mono: 9.. _v4l2-pix-fmt-pisp-comp2-rggb: 10.. _v4l2-pix-fmt-pisp-comp2-grbg: 11.. _v4l2-pix-fmt-pisp-comp2-gbrg: 12.. _v4l2-pix-fmt-pisp-comp2-bggr: 13.. _v4l2-pix-fmt-pisp-comp2-mono: 14 15************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************** 16V4L2_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') 17************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************** 18 19================================================ 20Raspberry Pi PiSP compressed 8-bit Bayer formats 21================================================ 22 23Description 24=========== 25 26The Raspberry Pi ISP (PiSP) uses a family of three fixed-rate compressed Bayer 27formats. A black-level offset may be subtracted to improve compression 28efficiency; the nominal black level and amount of offset must be signalled out 29of band. Each scanline is padded to a multiple of 8 pixels wide, and each block 30of 8 horizontally-contiguous pixels is coded using 8 bytes. 31 32Mode 1 uses a quantization and delta-based coding scheme which preserves up to 3312 significant bits. Mode 2 is a simple sqrt-like companding scheme with 6 PWL 34chords, preserving up to 12 significant bits. Mode 3 combines both companding 35(with 4 chords) and the delta scheme, preserving up to 14 significant bits. 36 37The remainder of this description applies to Modes 1 and 3. 38 39Each block of 8 pixels is separated into even and odd phases of 4 pixels, 40coded independently by 32-bit words at successive locations in memory. 41The two LS bits of each 32-bit word give its "quantization mode". 42 43In quantization mode 0, the lowest 321 quantization levels are multiples of 44FSD/4096 and the remaining levels are successive multiples of FSD/2048. 45Quantization modes 1 and 2 use linear quantization with step sizes of 46FSD/1024 and FSD/512 respectively. Each of the four pixels is quantized 47independently, with rounding to the nearest level. 48In quantization mode 2 where the middle two samples have quantized values 49(q1,q2) both in the range [384..511], they are coded using 9 bits for q1 50followed by 7 bits for (q2 & 127). Otherwise, for quantization modes 510, 1 and 2: a 9-bit field encodes MIN(q1,q2) which must be in the range 52[0..511] and a 7-bit field encodes (q2-q1+64) which must be in [0..127]. 53 54Each of the outer samples (q0,q3) is encoded using a 7-bit field based 55on its inner neighbour q1 or q2. In quantization mode 2 where the inner 56sample has a quantized value in the range [448..511], the field value is 57(q0-384). Otherwise for quantization modes 0, 1 and 2: The outer sample 58is encoded as (q0-MAX(0,q1-64)). q3 is likewise coded based on q2. 59Each of these values must be in the range [0..127]. All these fields 60of 2, 9, 7, 7, 7 bits respectively are packed in little-endian order 61to give a 32-bit word with LE byte order. 62 63Quantization mode 3 has a "7.5-bit" escape, used when none of the above 64encodings will fit. Each pixel value is quantized to the nearest of 176 65levels, where the lowest 95 levels are multiples of FSD/256 and the 66remaining levels are multiples of FSD/128 (level 175 represents values 67very close to FSD and may require saturating arithmetic to decode). 68 69Each pair of quantized pixels (q0,q1) or (q2,q3) is jointly coded 70by a 15-bit field: 2816*(q0>>4) + 16*q1 + (q0&15). 71Three fields of 2, 15, 15 bits are packed in LE order {15,15,2}. 72 73An implementation of a software decoder of compressed formats is available 74in `Raspberry Pi camera applications code base 75<https://github.com/raspberrypi/rpicam-apps/blob/main/image/dng.cpp>`_. 76