libavcodec/pixdesc.h

   1 /*
   2  * pixel format descriptor
   3  * Copyright (c) 2009 Michael Niedermayer <michaelni@gmx.at>
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * FFmpeg is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with FFmpeg; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 #include <inttypes.h>
  23
  24 #include "libavutil/intreadwrite.h"
  25 #include "get_bits.h"
  26
  27 typedef struct AVComponentDescriptor{
  28     uint16_t plane        :2;            ///< which of the 4 planes contains the component
  29
  30     /**
  31      * Number of elements between 2 horizontally consecutive pixels minus 1.
  32      * Elements are bits for bitstream formats, bytes otherwise.
  33      */
  34     uint16_t step_minus1  :3;
  35
  36     /**
  37      * Number of elements before the component of the first pixel plus 1.
  38      * Elements are bits for bitstream formats, bytes otherwise.
  39      */
  40     uint16_t offset_plus1 :3;
  41     uint16_t shift        :3;            ///< number of least significant bits that must be shifted away to get the value
  42     uint16_t depth_minus1 :4;            ///< number of bits in the component minus 1
  43 }AVComponentDescriptor;
  44
  45 /**
  46  * Descriptor that unambiguously describes how the bits of a pixel are
  47  * stored in the up to 4 data planes of an image. It also stores the
  48  * subsampling factors and number of components.
  49  *
  50  * @note This is separate of the colorspace (RGB, YCbCr, YPbPr, JPEG-style YUV
  51  *       and all the YUV variants) AVPixFmtDescriptor just stores how values
  52  *       are stored not what these values represent.
  53  */
  54 typedef struct AVPixFmtDescriptor{
  55     const char *name;
  56     uint8_t nb_channels;        ///< The number of components each pixel has, (1-4)
  57
  58     /**
  59      * Amount to shift the luma width right to find the chroma width.
  60      * For YV12 this is 1 for example.
  61      * chroma_width = -((-luma_width) >> log2_chroma_w)
  62      * The note above is needed to ensure rounding up.
  63      */
  64     uint8_t log2_chroma_w;      ///< chroma_width = -((-luma_width )>>log2_chroma_w)
  65
  66     /**
  67      * Amount to shift the luma height right to find the chroma height.
  68      * For YV12 this is 1 for example.
  69      * chroma_height= -((-luma_height) >> log2_chroma_h)
  70      * The note above is needed to ensure rounding up.
  71      */
  72     uint8_t log2_chroma_h;
  73     uint8_t flags;
  74     AVComponentDescriptor comp[4]; ///< parameters that describe how pixels are packed
  75 }AVPixFmtDescriptor;
  76
  77 #define PIX_FMT_BE        1 ///< big-endian
  78 #define PIX_FMT_PAL       2 ///< Pixel format has a palette in data[1], values are indexes in this palette.
  79 #define PIX_FMT_BITSTREAM 4 ///< All values of a component are bit-wise packed end to end.
  80
  81 /**
  82  * The array of all the pixel format descriptors.
  83  */
  84 extern const AVPixFmtDescriptor av_pix_fmt_descriptors[];
  85
  86 /**
  87  * Reads a line from an image, and writes to \p dst the values of the
  88  * pixel format component \p c.
  89  *
  90  * @param data the array containing the pointers to the planes of the image
  91  * @param linesizes the array containing the linesizes of the image
  92  * @param desc the pixel format descriptor for the image
  93  * @param x the horizontal coordinate of the first pixel to read
  94  * @param y the vertical coordinate of the first pixel to read
  95  * @param w the width of the line to read, that is the number of
  96  * values to write to \p dst
  97  * @param read_pal_component if not zero and the format is a paletted
  98  * format writes to \p dst the values corresponding to the palette
  99  * component \p c in data[1], rather than the palette indexes in
 100  * data[0]. The behavior is undefined if the format is not paletted.
 101  */
 102 static inline void read_line(uint16_t *dst, const uint8_t *data[4], const int linesize[4],
 103                              const AVPixFmtDescriptor *desc, int x, int y, int c, int w, int read_pal_component)
 104 {
 105     AVComponentDescriptor comp= desc->comp[c];
 106     int plane= comp.plane;
 107     int depth= comp.depth_minus1+1;
 108     int mask = (1<<depth)-1;
 109     int shift= comp.shift;
 110     int step = comp.step_minus1+1;
 111     int flags= desc->flags;
 112
 113     if (flags & PIX_FMT_BITSTREAM){
 114         GetBitContext gb;
 115         init_get_bits(&gb, data[plane] + y*linesize[plane], linesize[plane]*8);
 116         skip_bits_long(&gb, x*step + comp.offset_plus1-1);
 117
 118         while(w--){
 119             int val = show_bits(&gb, depth);
 120             if(read_pal_component)
 121                 val= data[1][4*val + c];
 122             skip_bits(&gb, step);
 123             *dst++= val;
 124         }
 125     } else {
 126         const uint8_t *p = data[plane]+ y*linesize[plane] + x*step + comp.offset_plus1-1;
 127
 128         while(w--){
 129             int val;
 130             if(flags & PIX_FMT_BE) val= AV_RB16(p);
 131             else                   val= AV_RL16(p);
 132             val = (val>>shift) & mask;
 133             if(read_pal_component)
 134                 val= data[1][4*val + c];
 135             p+= step;
 136             *dst++= val;
 137         }
 138     }
 139 }