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• Converting limited range YUV to sRGB using ImageMagick

  6 juillet 2019, par Rotem

  I am trying to convert a set of raw video frames from YUV444 to sRGB using ImageMagick.

  Input format : Raw YUV444 limited range, BT.709 in planar data order.
  Required output format : sRGB (set of PNG images).

  Main issue : ImageMagick conversion always applies JPEG conversion formula.

  • Remark about "limited range" YUV format :
    In 8 bits limited range YUV format, the range of Y is [16, 235] and the range of U, V is [16, 240]. (limited range BT.709 is used in HTDV systems).
    JPEG uses "full range" YUV format, where Y,U,V range is [0, 255].
    sRGB is used in PC systems, and the range of R,G,B is full range [0, 255].
    YUV and YCbCr are interchangeable.

  For testing, I used the following sample image :

  • Sample image in sRGB format (rgb_input.png) :
    

  I converted the sample to YUV444 format using FFmpeg :
  ffmpeg -y -colorspace bt709 -i rgb_input.png -pix_fmt yuv444p yuv_input.yuv

  Following image illustrates the YUV444 output (in planar data order) :

  • Input image for ImageMagick in YUV444 format (yuv_input.yuv planar data order illustration) :
    

  I converted yuv_input.yuv to PNG using ImageMagick converter (version 7.0.8-51) :
  magick -depth 8 -interlace plane -size 128x96 -colorspace Rec709YCbCr -sampling-factor 4:4:4 yuv:yuv_input.yuv rgb_output_magick.png

  • Result of ImageMagick (rgb_output_magick.png) :
    
    If you look carefully you see that the image is different than rgb_input.png.

  Same conversion using FFmpeg (used as reference) :
  ffmpeg -y -s 128x96 -colorspace bt709 -pix_fmt yuv444p -i yuv_input.yuv -pix_fmt rgb24 rgb_output_ffmpeg.png

  • Result of FFmpeg (rgb_output_ffmpeg.png) :
    
    Note : The true format of my raw input video frames prevents me from using FFmpeg.

  Conversion formula from 8 bits limited range YUV BT.709 to sRGB :
  R = 1.1644*Y + 0.00000*U + 1.79270*V - 248.10
G = 1.1644*Y - 0.21325*U - 0.53291*V + 76.878
B = 1.1644*Y + 2.11240*U + 0.00000*V - 289.02

  How can I do the above conversion using ImageMagick converter ?

• lavu/opt : apply range checks also when setting format string value

  16 décembre 2013, par Stefano Sabatini

  lavu/opt : apply range checks also when setting format string value
  Previously when setting a pixel/sample format as a string range checks
  
  were not performed. This is consistent with the
  
  av_opt_set_pixel/sample_fmt() interface.
  

  • [DH] libavutil/opt.c

• Audio merge modify video length

  15 septembre 2022, par sfarzoso

  I'm trying to merge an audio soundtrackPath to a video videoPath, so I wrote this script :

  


  ffmpeg -i $videoPath -i '$soundtrackPath' -c:v copy \
-filter_complex \"[0:a]aformat=fltp:44100:stereo,apad[0a];[1]aformat=fltp:44100:stereo,volume=1.5[1a];[0a][1a]amerge[a]\" \
-map 0:v -map \"[a]\" -ac 2 $outputPath 2>log.txt


  


  which is working but there are two issues that I don't know how to fix :

  


  

  1. Merge audio is too low, is possible decrease the volume of soundtrackPath ?

  


  2. Video lenght is 1:59 and the soundtrackPath is 3:29, the final result will modify the video length to 3:29, is possible to adapt the audio only for the video length ?