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Re: Read _ tiff with Sub_Rect Keyword [message #44995 is a reply to message #44876]

Wed, 27 July 2005 12:28

Chris[2]
Messages: 39
Registered: August 2003

Member

Couldn't you eliminate the loop entirely using stride?

image[*, *, m] = a[*,0:samples-1:xper+1]

Or, even better, since you are inserting the "a" array into a contiguous
block of memory in "image", you can just use 0,0 as the subscripts:

image[0, 0, m] = a[*,0:samples-1:xper+1]

This will insert the entire "a" subarray into "image", starting at position
[0,0]. This is *much* faster than using index ranges, or even the *'s,
because IDL doesn't have to compute the locations internally. It just copies
the data as one block.

One other point. I think you want just "xper" in your loop, not "xper+1".
And finally, if your image isn't a multiple of "xper", your array indexing
will run off the end. So I think you really want to compute ximg and yimg
as:
ximg = (samples + xper - 1)/xper
yimg = (lines + yper - 1)/yper

-Chris

<meinel@aero.org> wrote in message
news:1122383746.592213.326040@g44g2000cwa.googlegroups.com.. .
> Isn't it more efficient to write
>
> for j =0 ,samples-1,xper+1 do begin
> image[0:2,k,m] = a[0:2,j]
> k++
> endfor
>

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[Message index]

		Re: Read _ tiff with Sub_Rect Keyword By: edward.s.meinel@aero. on Tue, 26 July 2005 06:15
		Re: Read _ tiff with Sub_Rect Keyword By: raval.chintan on Tue, 26 July 2005 05:06
		Re: Read _ tiff with Sub_Rect Keyword By: Chris[2] on Mon, 25 July 2005 08:32
		Re: Read _ tiff with Sub_Rect Keyword By: raval.chintan on Mon, 25 July 2005 03:36
		Re: Read _ tiff with Sub_Rect Keyword By: btt on Fri, 22 July 2005 06:52
		Re: Read _ tiff with Sub_Rect Keyword By: Chris[2] on Wed, 27 July 2005 12:28

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