| Re: Zoom out of astronomical image preserving header info [message #42666 is a reply to message #42625] |
Fri, 18 February 2005 13:34   |
mperrin+news
Messages: 81
Registered: May 2001
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burkina <stebia@inwind.it> wrote:
> The problem with hrebin (and hcongrid) is that they don't zoom the
> image out as I need (like atv for example). They will produce an image
> with that number of pixels, so that if the zoom factor is 2, an
> original image of, say, 300x300, will become 600x600. This means a lot
> of time in processing the image when you need a very large zoom factor
> (as in my case) and enormous image files. That's not what I need. I
> actually need a costant image size, but with the original image
> shrinked to the desired dimension.
> In practice, I need a functionality completely equivalent to the ATV
> zoom, together with the possibility to re-center the final image where
> I want. I need space outside the image with the correct RA and DEC
> coordinates. ATV does it, but it can't do other things I need. That's
> why I can't use it directly.
In that case, may I suggest that you read through the atv source and copy
the algorithms from there? ATV is actually fairly well written and I think
it's not too difficult to pull out the relevant sections.
In particular, look at atv_getdisplay for the code that actually
resizes the array using congrid and embeds it into a larger fixed-size
array initialized to all zeros. You may have some more complicated
manipulations needed to get the astrometry header to match correctly.
What you really want is to resize the image to a smaller size and then
embed it in a larger array, I think. The first part is easy with
HCONGRID. The second needs the inverse of HEXTRACT, which doesn't seem
to exist yet. (HEMBED?) Maybe if you end up writing such a thing, you
could consider contributing it to the library!
- Marshall
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