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From: Ullrich Koethe (koethe_at_[hidden])
Date: 2006-11-01 15:55:09

Hi all,

I'm back in the discussion.

François Duranleau wrote:
> Now it's my take about color vs pixel :)
> I don't understand why pixel is a bad name. For someone in the graphics
> community, pixel really is the right name. The term pixel stands for
> picture element, and it seems to me that GIL's pixel is exactly that: an
> element in a raster image.

I disagree. An image is a collection of sampling points with associated
sample values. Each sampling point defines a pixel, which is the Voronoi
region around the sampling point (i.e. the set of points in the Euclidean
plane that is nearest to a particular sampling point). In a square raster,
the sampling points are conveniently located at integer coordinates, so
that the pixels become squares. Sampling points and pixels are therefore
geometric entities (points and regions in the plane), whereas pixel values
can essentially live in an arbitrary domain. For convenience, the term
pixel is often used as a synonym for sampling point, but it cannot be the
pixel value at the same time.

Consequently, the right term is pixel_value, and GIL is halfway right,
because the associated typedef is already called pixel_value_type. Calling
the concept itself pixel_value would just be consequent, IMHO. Parhaps,
just using 'value' and 'value_type' would be even simpler (because 'pixel'
is implied by the image data structure).


PS. I'm working on a detailed review. I hope it is still of useful after 
the review deadline.
|                                                                |
| Ullrich Koethe  Universitaet Hamburg / University of Hamburg   |
|                 FB Informatik        / Dept. of Informatics    |
|                 AB Kognitive Systeme / Cognitive Systems Group |
|                                                                |
| Phone: +49 (0)40 42883-2573                Vogt-Koelln-Str. 30 |
| Fax:   +49 (0)40 42883-2572                D - 22527 Hamburg   |
| Email: u.koethe_at_[hidden]               Germany             |
|        koethe_at_[hidden]                        |
| WWW:      |

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