Resumen

The picture is of the John Moulton Barn at the base of the Teton Range.

Raison d'être

This is a cleaner/more acurate version of en:Image:YUV_components.jpg. The improvements are:

• Use a lossless compression algorithm, PNG removing jpeg artifacts
• Don't scale U, V to extreme values - use the raw value, which more closely approximates the chroma component
• Fix the inverted polarity of U, V components

Generation

To generate this map Brian Szymanski used this perl script, and then ran optipng with a full search to shrink the filesize. If you want to understand the below code, you should probably use perltidy - the code is mostly here for my reference, but it is wrong. The first channel of the blue/yellow map has to be set to U as well and the third channel of the red/green map has to be set to 0.5. I will fix it soon and update the image.

perl -e 'use strict; use warnings; use GD; GD::Image->trueColor(1);
my %color_cache;
sub cached_allocate { my $img = shift; my @rgb = @_;
   my $rgb = join(",", @rgb);
   $color_cache{$rgb} = $img->colorAllocate(@rgb) unless($color_cache{$rgb});
   return $color_cache{$rgb};
}

my $img = GD::Image->new("barn.png");
my ($height, $width) = ($img->height, $img->width);
my $yuv_img = GD::Image->new($width, $height*4);
foreach my $y (0..$height-1) {
   foreach my $x (0..$width-1) {
      my ($r, $g, $b) = map { $_ / 256 } my @rgb = $img->rgb($img->getPixel($x, $y));
      my $Y = 0.299*$r+0.587*$g+0.114*$b;
      my $U = 0.436*($b-$Y)/(1-0.114);
      my $V = 0.615*($r-$Y)/(1-0.299);
      $Y *= 256;
      $U += .436; $U *= (256/.872);
      $V += .615; $V *= (256/1.23);
      ($Y, $U, $V) = map { int(0.5+$_) } ($Y, $U, $V);
      die "YUV: $Y,$U,$V" if (($Y > 255) or ($U > 255) or ($V > 255));
      $yuv_img->setPixel($x, $y, cached_allocate($yuv_img, @rgb));
      $yuv_img->setPixel($x, $height+$y, cached_allocate($yuv_img, $Y, $Y, $Y));
      $yuv_img->setPixel($x, 2*$height+$y, cached_allocate($yuv_img, 0, 255-$U, $U));
      $yuv_img->setPixel($x, 3*$height+$y, cached_allocate($yuv_img, $V, 255-$V, 0));
   }
};
print $yuv_img->png' >barn-yuv.png

Licencia

Yo, el titular de los derechos de autor de esta obra, lo libero al dominio público. Esto aplica en todo el mundo. En algunos países esto puede no ser legalmente factible; si ello ocurriese: Concedo a cualquier persona el derecho de usar este trabajo para cualquier propósito, sin ningún tipo de condición al menos que éstas sean requeridas por la ley.