src/libcamera/formats.cpp


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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2019, Google Inc.
 *
 * formats.cpp - libcamera image formats
 */

#include "libcamera/internal/formats.h"

#include <algorithm>
#include <errno.h>

#include <libcamera/base/log.h>
#include <libcamera/base/utils.h>

#include <libcamera/formats.h>

/**
 * \file internal/formats.h
 * \brief Types and helper functions to handle libcamera image formats
 */

namespace libcamera {

LOG_DEFINE_CATEGORY(Formats)

/**
 * \class PixelFormatInfo
 * \brief Information about pixel formats
 *
 * The PixelFormatInfo class groups together information describing a pixel
 * format. It facilitates handling of pixel formats by providing data commonly
 * used in pipeline handlers.
 *
 * \var PixelFormatInfo::name
 * \brief The format name as a human-readable string, used as the test
 * representation of the PixelFormat
 *
 * \var PixelFormatInfo::format
 * \brief The PixelFormat described by this instance
 *
 * \var PixelFormatInfo::v4l2Formats
 * \brief The V4L2 pixel formats corresponding to the PixelFormat
 *
 * Multiple V4L2 formats may exist for one PixelFormat when the format uses
 * multiple planes, as V4L2 defines separate 4CCs for contiguous and separate
 * planes formats. The two entries in the array store the contiguous and
 * non-contiguous V4L2 formats respectively. If the PixelFormat isn't a
 * multiplanar format, or if no corresponding non-contiguous V4L2 format
 * exists, the second entry is invalid.
 *
 * \var PixelFormatInfo::bitsPerPixel
 * \brief The average number of bits per pixel
 *
 * The number per pixel averages the total number of bits for all colour
 * components over the whole image, excluding any padding bits or padding
 * pixels.
 *
 * For formats that store pixels with bit padding within words, only the
 * effective bits are taken into account. For instance, 12-bit Bayer data
 * stored in two bytes per pixel report 12, not 16, in this field.
 *
 * Formats that don't have a fixed number of bits per pixel, such as compressed
 * formats, report 0 in this field.
 *
 * \var PixelFormatInfo::colourEncoding
 * \brief The colour encoding type
 *
 * \var PixelFormatInfo::packed
 * \brief Tell if multiple pixels are packed in the same bytes
 *
 * Packed formats are defined as storing data from multiple pixels in the same
 * bytes. For instance, 12-bit Bayer data with two pixels stored in three bytes
 * is packed, while the same data stored with 4 bits of padding in two bytes
 * per pixel is not packed.
 *
 * \var PixelFormatInfo::pixelsPerGroup
 * \brief The number of pixels in a pixel group
 *
 * A pixel group is defined as the minimum number of pixels (including padding)
 * necessary in a row when the image has only one column of effective pixels.
 * pixelsPerGroup refers to this value. PixelFormatInfo::Plane::bytesPerGroup,
 * then, refers to the number of bytes that a pixel group consumes. This
 * definition of a pixel group allows simple calculation of stride, as
 * ceil(width / pixelsPerGroup) * bytesPerGroup. These values are determined
 * only in terms of a row. The ceiling accounts for padding.
 *
 * A pixel group has a second constraint, such that the pixel group
 * (bytesPerGroup and pixelsPerGroup) is the smallest repeatable unit.
 * What this means is that, for example, in the IPU3 formats, if there is only
 * one column of effective pixels, it looks like it could be fit in 5 bytes
 * with 3 padding pixels (for a total of 4 pixels over 5 bytes). However, this
 * unit is not repeatable, as at the 7th group in the same row, the pattern
 * is broken. Therefore, the pixel group for IPU3 formats must be 25 pixels
 * over 32 bytes.
 *
 * For example, for something simple like BGR888, it is self-explanatory:
 * the pixel group size is 1, and the bytes necessary is 3, and there is
 * only one plane with no (= 1) vertical subsampling. For YUYV, the
 * CbCr pair is shared between two pixels, so even if you have only one
 * pixel, you would still need a padded second Y sample, therefore the pixel
 * group size is 2, and bytes necessary is 4. YUYV also has no vertical
 * subsampling. NV12 has a pixel group size of 2 pixels, due to the CbCr plane.
 * The bytes per group then, for both planes, is 2. The first plane has no
 * vertical subsampling, but the second plane is subsampled by a factor of 2.
 *
 * The IPU3 raw Bayer formats are single-planar, and have a pixel group size of
 * 25, consuming 32 bytes, due to the packing pattern being repeated in memory
 * every 32 bytes. The IPU3 hardware, however, has an additional constraint on
 * the DMA burst size, requiring lines to be multiple of 64 bytes. This isn't an