[NTG-context] CMYK colors not as expected

Hans Hagen pragma at wxs.nl
Wed Jun 29 10:10:58 CEST 2011

On 28-6-2011 2:06, Hans van der Meer wrote:
> I would be pleased to get some advice from "color-knowledgeable people" on the following matter.
> In TV-broadcasts there are usually two kinds of subtitles present: Teletext as characters and DVB as pixels. These can be extracted and rendered with Metapost. I have done this, but I am not very satisfied with the colors produced. On the television screen they look bright, when rendered in Metapost they are dull and muddy. The text is barely readable.
> As I am fairly sure I did extract the correct bits from the CLUT contained in the stream, I wonder if I am doing something not right at the Metapost side. In the datastream the values given are the most significant 6, 4, 4 and 2 bits of respectively Y, Cr, Cb, T. These are scaled to the values given to Metapost by dividing them by 255.
> In the zip one finds the program (ConTeXt MKIV) used for typesetting, an example pixel map with clut, and the output. I would be obliged to get some comments.

As you're doing a lot of calculations, you can consider using bitmaps


         bitmapimage(2,2,"334455 667788 99aabb ccddee")
         scaled 3cm
         rotated 15 ;
         bitmapimage(2,2,"33 55 77 99")
         scaled 2cm
         rotated 30 ;
         bitmapimage(2,2,"0000ff00 ff00ff00 00ff0000 ffff0000")
         scaled 1cm
         rotated 45 ;


                                           Hans Hagen | PRAGMA ADE
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