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Re: reading pixels from images from automated XYpositions [message #39007 is a reply to message #38994]

Wed, 14 April 2004 16:02

Yunxiang Zhang
Messages: 19
Registered: October 2003

Junior Member

I think you'd better explain in detail the definition of your pos. I can't
understand it from your code. But I think I may have a similiar question
of how to extract features from an image.

For example, let's define a 7X7 pixels area a molecule. And I have all N
molecules' positions stored in a 2XN array pos. Thus, molecule No. i will
be,

Image[pos[0,i]-3:pos[0,i]+3,pos[1,i]-3:pos[1,i]+3]

which is a 7X7 data. But if if I want to extract all the molecules at the
same time without using a loop. Then I got,

molecules=Image[pos[0,*]-3:pos[0,*]+3,pos[1,*]-3:pos[1,*]+3]

% Expression must be a scalar or 1 element array in this context: <INT
Array[1, N]>.

Can anybody show me how to do this properly?

Thanks!
Yunxiang

On Wed, 14 Apr 2004, Thomas Nehls wrote:

> Hi folks,
>
> I want to get information(mean, stddev, median) about the values of
> certain pixels(7x7 pixels areas) from an image.
> The according XY positions should be read from a file, where a list of
> positions is given.
>
> This is, what I thought could work:
>
>> PRO input,x
>>
>> FOR n=0,x-1 do grey_scale_value,n
>> END
>>
>> PRO grey_scale_value, n,x
>> file = DIALOG_PICKFILE(/READ)
>> img = READ_TIFF(file)
>> positions = DIALOG_PICKFILE(/READ)
>> pos =bytarr(3,6)
>> pos = READ_SYLK(positions,/ARRAY)
>> pixels1 = img[0,23:26,35:38]
>> pixels2 = img[0,(pos[1]-3 where pos[0]=n):(pos[1]+3 where pos[0]=n),(pos[2]-3 where pos[0]=n):(pos[2]+3 where pos[0]=n)]
>>
>> OPENW,1,'greyscale_data.dat',/APPEND
>> PRINTF,1, (n+1),mean(pixels2),stddev(pixels2),median(pixels2)
>> CLOSE,1
>> END
>
> first I tried pixels1, the scheme works, but I think I used the 'where'
> command in the wrong way...
> Do you have a hint for me?
> Thanks
> Tom
>
>

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[Message index]

		Re: reading pixels from images from automated XYpositions By: Thomas Nehls on Fri, 16 April 2004 04:58
		Re: reading pixels from images from automated XYpositions By: Rick Towler on Thu, 15 April 2004 09:50
		Re: reading pixels from images from automated XYpositions By: Thomas Nehls on Thu, 15 April 2004 09:23
		Re: reading pixels from images from automated XYpositions By: Yunxiang Zhang on Wed, 14 April 2004 16:02

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