Re: OT: Looking for image file format that can handle 16b its per channel

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#114

From: Oliver Kreylos
Date: Thu, 30 Dec 1999 00:00

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Paul Richards wrote:
[snip]
> ASCII PPM?  What do you mean by that?  The PPM's I currently can make
> have the header in ASCII, and they do have a "maxValue" field but the
> data is just raw binary.
> 
> Could you explain a little further on how these ASCII ones work?

Well, I can try...

The header for an ASCII ppm is the code P3, followed by width, height
and maxValue, as usual. Note that the values for those fields are given
in ASCII - I mean, they are printed out.

In a "raw" or binary ppm file, the code is a P6, and the image data is
written as a series of bytes - three per pixel. In the ASCII format,
each pixel is written as three integer values - all spelled out.
Example:

P3
2 2 1000

   0    0    0       0 1000    0

1000    0    0    1000 1000 1000

The maxVal field can be arbitrarily large (well, let's say it *can* be
65535), so you can effectively store 16 bits per channel per pixel.

HTH,

  Oliver

-- 
Email: kreylos@cs.ucdavis.edu
WWW:   http://graphics.cs.ucdavis.edu/~okreylos

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From: Oliver Kreylos <kreylos@cs.ucdavis.edu>
Subject: Re: OT:  Looking for image file format that can handle 16b its per  channel
Date: 1999/12/30
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