[fitsbits] top or buttom

[Stephen Walton]

One point about this which I've always found somewhat confusing (though
maybe I'm the only one):  We usually consider the indices of an array
stored in memory as being (row,column) by analogy to mathematical
matrices.  But, if we adopt the convention that the first axis of a FITS
image is displayed horizontally and the second vertically, the first index
of the array is, in effect, the column index;  i.e., the Y coordinate.  
Suppose you read a FITS image into MATLAB witth the first index of the
FITS image corresponding to the first index of the array in which it is
stored.  If you use the MATLAB image toolbox to display that image it will
be transposed from what you're used to, because it displays the image
array as if it were a mathematical matrix, with element (1,1) in the upper
left corner and the first (i.e., row) index increasing vertically
downward.

--
Stephen Walton, Professor of Physics and Astronomy
California State University, Northridge
stephen.walton at csun.edu

On Wed, 19 Apr 2000, Eric Greisen wrote:

> The proposed WCS convention paper states:
> 
> 
> \subsection{Image display conventions}
> 
> It is very helpful to adopt a convention for the display of images
> transferred via the FITS format.  Many of the current image processing
> systems have converged upon such a convention.  Therefore, we
> recommend that FITS writers order the pixels so that the first pixel
> in the FITS file (for each image plane) be the one that would be
> displayed in the lower-left corner (with the first axis increasing to
> the right and the second axis increasing upwards)...