image processing - How to convert a jpg to yuv in C? -

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even though question of nature sounds similar, having problems in converting jpg image yuv in c (without using opencv).

this have understood of now, how solve problem :

  1. identify structure of file formats jpg , yuv. i.e each byte in file contains. think jpg format looks like.
  2. with above structure tried read jpg file , tried decipher 18th , 19th bytes. did type cast them both char , int don`t meaningful values width , height of image.

  3. once have read these values, should able convert them jpg yuv. looking @ resource.

  4. appropriately, construct yuv image , write (.yuv) file.

kindly me pointing me appropriate resources. keep updating progress on post. in advance.

based on https://en.wikipedia.org/wiki/yuv#y.27uv444_to_rgb888_conversion

yuv conversion

decoding jpeg, in pure c without libraries ... following code straightforward ...

https://bitbucket.org/halicery/firerainbow-progressive-jpeg-decoder/src

assuming have jpeg decoded rgb using above or library (using library easier).

int width = (width of image); int height = (height of image); byte *mydata = (pointer rgb pixels); byte *cursor; size_t byte_count = (length of pixels .... i.e. width x height x 3); int n; (cursor = mydata, n = 0; n < byte_count; cursor += 3, n += 3)  {     int red = cursor[0], green = cursor[1], blue = cursor[2];     int y = 0.299 * red + 0.587 * green + 0.114 * blue;     int u = -0.147 * red + -0.289 * green + 0.436 * blue;     int v = 0.615 * red + -0.515 * green + -0.100 * blue;      cursor[0] = y, cursor[1] = u, cursor[2] = v; }  // @ point, entire image has been converted yuv ...

and write file ...

file* fout = fopen ("myfile.yuv, "wb");  if (fout) {     fwrite (mydata, 1, byte_count, fout);     fclose (fout); }

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