| Re: Array resize with arbitrary arithmetic [message #52942] |
Mon, 12 March 2007 15:15  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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David Fanning writes:
>> image=read_bmp('9 March 2007\775u.bmp') ; 640x240 array
>> temp = Rebin(image, 2, 320, 240)
>> temp = Total(Temporary(temp), 1)
>
> Whoops, that REBIN command should be REFORM. :-)
Let this be a lesson to those of you who think you
can answer IDL questions at the same time you are
working on something else. Sheesh!
I *think* the answer to the original question, which
looks to me like we want to multiply the first pixel
by 256 and add the second, adjacent pixel to it (does
that seem weird to you!?) is this:
image=read_bmp('9 March 2007\775u.bmp') ; 640x240 array
temp = Rebin(image, 2, 320, 240) ; Adjacent pixels in cols
temp[0,*,*] = temp[0,*,*] * 256 ; Multiply 1st col by 256.
temp = Total(temp,1) ; Add columns together.
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: Array resize with arbitrary arithmetic [message #52944 is a reply to message #52943] |
Mon, 12 March 2007 14:50  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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rpertaub@gmail.com writes:
> I have this 640x240 array. I need to change it to a 320x240 array.
> However, in first array, consecutive 2 pixels hold information for 1
> pixel in second array and I need to do a certain bit of arithmetic to
> obtain that. This should not be too difficult, except I keep getting
> errors and I am not sure why:
> This is what I do:
>
> pro compress_image
>
> image=read_bmp('9 March 2007\775u.bmp') ; 640x240 array
>
> comp_image=make_array(76800,/long) ;1x76800 array that I can
> reform to 320x240array later
>
> temp=0
>
> for j=0,239 DO BEGIN
> for i=0,319 DO BEGIN
>
> comp_image[0,temp]= image[2*i,j]*256 + image[2*i+1,j] ;
> arithmetic necessary
> temp=temp+1
> endfor
>
> endfor
>
>
> end
Seems to me the way to do this might be like this:
image=read_bmp('9 March 2007\775u.bmp') ; 640x240 array
temp = Rebin(image, 2, 320, 240)
temp = Total(Temporary(temp), 1)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: Array resize with arbitrary arithmetic [message #53010 is a reply to message #52942] |
Tue, 13 March 2007 20:26 |
Dick Jackson
Messages: 347
Registered: August 1998
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Senior Member |
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Hi Radha,
"David Fanning" <news@dfanning.com> wrote in message
news:MPG.205f7ed4a7dbb8da989ed1@news.frii.com...
> David Fanning writes:
>
>>> image=read_bmp('9 March 2007\775u.bmp') ; 640x240 array
>>> temp = Rebin(image, 2, 320, 240)
>>> temp = Total(Temporary(temp), 1)
> [...]
> I *think* the answer to the original question, which
> looks to me like we want to multiply the first pixel
> by 256 and add the second, adjacent pixel to it (does
> that seem weird to you!?) is this:
>
> image=read_bmp('9 March 2007\775u.bmp') ; 640x240 array
> temp = Rebin(image, 2, 320, 240) ; Adjacent pixels in cols
> temp[0,*,*] = temp[0,*,*] * 256 ; Multiply 1st col by 256.
> temp = Total(temp,1) ; Add columns together.
That's not bad, but if I'm right, this arithmetic isn't so arbitrary! We're just
turning each pair of bytes into an unsigned short integer, so this one line
should do the whole thing:
comp_image = UInt(image, 0, 320, 240)
... except if you're on a "little-endian" machine, you'll need to swap the
bytes. This statement will work to fix it if needed:
Swap_Endian_InPlace, comp_image, /Swap_If_Little_Endian
Now, I don't have your data, but this test should prove the point. I tested it
on Intel (little-endian) and works fine, can someone double-check it on
big-endian hardware, please?
IDL> image=bindgen(6,2)*21B
IDL> print,image
0 21 42 63 84 105
126 147 168 189 210 231
IDL> comp_image = UInt(image, 0, 3, 2)
IDL> Swap_Endian_InPlace, comp_image, /Swap_If_Little_Endian
IDL> print,comp_image
21 10815 21609
32403 43197 53991
If you really need the result as Long, then *after* all this, do
comp_image = Long(comp_image)
Hope this helps!
--
Cheers,
-Dick
--
Dick Jackson Software Consulting http://www.d-jackson.com
Victoria, BC, Canada +1-250-220-6117 dick@d-jackson.com
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