From 5d6318f242cce5f9b5677baedde736a2b81061df Mon Sep 17 00:00:00 2001 From: Jacopo Mondi Date: Wed, 17 Jan 2024 11:21:50 +0200 Subject: [PATCH 1151/1215] media: uapi: Document PiSP Compressed RAW Bayer formats Document the Raspberry Pi compressed RAW Bayer formats. The compression algorithm description is provided by Nick Hollinghurst from Raspberry Pi. Signed-off-by: Jacopo Mondi Reviewed-by: Naushir Patuck --- .../userspace-api/media/v4l/pixfmt-bayer.rst | 1 + .../media/v4l/pixfmt-srggb8-pisp-comp.rst | 74 +++++++++++++++++++ 2 files changed, 75 insertions(+) create mode 100644 Documentation/userspace-api/media/v4l/pixfmt-srggb8-pisp-comp.rst --- a/Documentation/userspace-api/media/v4l/pixfmt-bayer.rst +++ b/Documentation/userspace-api/media/v4l/pixfmt-bayer.rst @@ -20,6 +20,7 @@ orders. See also `the Wikipedia article :maxdepth: 1 pixfmt-srggb8 + pixfmt-srggb8-pisp-comp pixfmt-srggb10 pixfmt-srggb10p pixfmt-srggb10alaw8 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/pixfmt-srggb8-pisp-comp.rst @@ -0,0 +1,74 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later + +.. _v4l2-pix-fmt-pisp-comp1-rggb: +.. _v4l2-pix-fmt-pisp-comp1-grbg: +.. _v4l2-pix-fmt-pisp-comp1-gbrg: +.. _v4l2-pix-fmt-pisp-comp1-bggr: +.. _v4l2-pix-fmt-pisp-comp1-mono: +.. _v4l2-pix-fmt-pisp-comp2-rggb: +.. _v4l2-pix-fmt-pisp-comp2-grbg: +.. _v4l2-pix-fmt-pisp-comp2-gbrg: +.. _v4l2-pix-fmt-pisp-comp2-bggr: +.. _v4l2-pix-fmt-pisp-comp2-mono: + +************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************** +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') +************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************************** + +================================================ +Raspberry Pi PiSP compressed 8-bit Bayer formats +================================================ + +Description +=========== + +The Raspberry Pi ISP (PiSP) uses a family of three fixed-rate compressed Bayer +formats. A black-level offset may be subtracted to improve compression +efficiency; the nominal black level and amount of offset must be signalled out +of band. Each scanline is padded to a multiple of 8 pixels wide, and each block +of 8 horizontally-contiguous pixels is coded using 8 bytes. + +Mode 1 uses a quantization and delta-based coding scheme which preserves up to +12 significant bits. Mode 2 is a simple sqrt-like companding scheme with 6 PWL +chords, preserving up to 12 significant bits. Mode 3 combines both companding +(with 4 chords) and the delta scheme, preserving up to 14 significant bits. + +The remainder of this description applies to Modes 1 and 3. + +Each block of 8 pixels is separated into even and odd phases of 4 pixels, +coded independently by 32-bit words at successive locations in memory. +The two LS bits of each 32-bit word give its "quantization mode". + +In quantization mode 0, the lowest 321 quantization levels are multiples of +FSD/4096 and the remaining levels are successive multiples of FSD/2048. +Quantization modes 1 and 2 use linear quantization with step sizes of +FSD/1024 and FSD/512 respectively. Each of the four pixels is quantized +independently, with rounding to the nearest level. +In quantization mode 2 where the middle two samples have quantized values +(q1,q2) both in the range [384..511], they are coded using 9 bits for q1 +followed by 7 bits for (q2 & 127). Otherwise, for quantization modes +0, 1 and 2: a 9-bit field encodes MIN(q1,q2) which must be in the range +[0..511] and a 7-bit field encodes (q2-q1+64) which must be in [0..127]. + +Each of the outer samples (q0,q3) is encoded using a 7-bit field based +on its inner neighbour q1 or q2. In quantization mode 2 where the inner +sample has a quantized value in the range [448..511], the field value is +(q0-384). Otherwise for quantization modes 0, 1 and 2: The outer sample +is encoded as (q0-MAX(0,q1-64)). q3 is likewise coded based on q2. +Each of these values must be in the range [0..127]. All these fields +of 2, 9, 7, 7, 7 bits respectively are packed in little-endian order +to give a 32-bit word with LE byte order. + +Quantization mode 3 has a "7.5-bit" escape, used when none of the above +encodings will fit. Each pixel value is quantized to the nearest of 176 +levels, where the lowest 95 levels are multiples of FSD/256 and the +remaining levels are multiples of FSD/128 (level 175 represents values +very close to FSD and may require saturating arithmetic to decode). + +Each pair of quantized pixels (q0,q1) or (q2,q3) is jointly coded +by a 15-bit field: 2816*(q0>>4) + 16*q1 + (q0&15). +Three fields of 2, 15, 15 bits are packed in LE order {15,15,2}. + +An implementation of a software decoder of compressed formats is available +in `Raspberry Pi camera applications code base +`_.