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. Hans van der Meer
2011/6/28 Hans van der Meer
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.
have you already seen http://en.wikipedia.org/wiki/YCbCr ? -- luigi
On 06/29/11 08:08, luigi scarso wrote:
have you already seen http://en.wikipedia.org/wiki/YCbCr
As luigi says, the Y/Cb/Cr (with or without T) is not CMYK, it is a different kind of color space altogether, and is conceptually much closer to RGB than to CMYK. The wiki page has equations to convert YCbCr to RGB. I have no idea what the 'K' component in your CLUT is supposed to be. Best wishes, Taco
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 \starttext \startMPpage draw bitmapimage(2,2,"334455 667788 99aabb ccddee") scaled 3cm rotated 15 ; draw bitmapimage(2,2,"33 55 77 99") scaled 2cm rotated 30 ; draw bitmapimage(2,2,"0000ff00 ff00ff00 00ff0000 ffff0000") scaled 1cm rotated 45 ; \stopMPpage \stoptext ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | voip: 087 875 68 74 | www.pragma-ade.com | www.pragma-pod.nl -----------------------------------------------------------------
participants (4)
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Hans Hagen -
Hans van der Meer -
luigi scarso -
Taco Hoekwater