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************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************** 15V4L2_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================================================ 19Raspberry Pi PiSP compressed 8-bit Bayer formats 20================================================ 21 22Description 23=========== 24 25The Raspberry Pi ISP (PiSP) uses a family of three fixed-rate compressed Bayer 26formats. A black-level offset may be subtracted to improve compression 27efficiency; the nominal black level and amount of offset must be signalled out 28of band. Each scanline is padded to a multiple of 8 pixels wide, and each block 29of 8 horizontally-contiguous pixels is coded using 8 bytes. 30 31Mode 1 uses a quantization and delta-based coding scheme which preserves up to 3212 significant bits. Mode 2 is a simple sqrt-like companding scheme with 6 PWL 33chords, 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 36The remainder of this description applies to Modes 1 and 3. 37 38Each block of 8 pixels is separated into even and odd phases of 4 pixels, 39coded independently by 32-bit words at successive locations in memory. 40The two LS bits of each 32-bit word give its "quantization mode". 41 42In quantization mode 0, the lowest 321 quantization levels are multiples of 43FSD/4096 and the remaining levels are successive multiples of FSD/2048. 44Quantization modes 1 and 2 use linear quantization with step sizes of 45FSD/1024 and FSD/512 respectively. Each of the four pixels is quantized 46independently, with rounding to the nearest level. 47In 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 49followed by 7 bits for (q2 & 127). Otherwise, for quantization modes 500, 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 53Each of the outer samples (q0,q3) is encoded using a 7-bit field based 54on its inner neighbour q1 or q2. In quantization mode 2 where the inner 55sample 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 57is encoded as (q0-MAX(0,q1-64)). q3 is likewise coded based on q2. 58Each of these values must be in the range [0..127]. All these fields 59of 2, 9, 7, 7, 7 bits respectively are packed in little-endian order 60to give a 32-bit word with LE byte order. 61 62Quantization mode 3 has a "7.5-bit" escape, used when none of the above 63encodings will fit. Each pixel value is quantized to the nearest of 176 64levels, where the lowest 95 levels are multiples of FSD/256 and the 65remaining levels are multiples of FSD/128 (level 175 represents values 66very close to FSD and may require saturating arithmetic to decode). 67 68Each pair of quantized pixels (q0,q1) or (q2,q3) is jointly coded 69by a 15-bit field: 2816*(q0>>4) + 16*q1 + (q0&15). 70Three fields of 2, 15, 15 bits are packed in LE order {15,15,2}. 71 72An implementation of a software decoder of compressed formats is available 73in `Raspberry Pi camera applications code base 74<https://github.com/raspberrypi/rpicam-apps/blob/main/image/dng.cpp>`_. 75