To find coordinates of the pixel having maximum counts

smp wrote on Mar 19, 2009

Hi,

I want to know whether there is any IRAF task which will tell (x,y) coordinates of that pixel which is having maximum counts , in a specified image section.

thanks
swapnil

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Mike Fitzpatrick wrote on Mar 19, 2009

See MINMAX.

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smp wrote on Mar 19, 2009

hi,

I tried MINMAX task. But it showed only minimum and maximum values for an image section.

It did not show (x,y) coordinates of those two pixels.

what I got is this:

im> minmax
Images to be examined (myimage.fits[1525:1570,520:540]): 

    myimage.fits[1525:1570,520:540] [46,3] 21.58049011230469 [20,9] 33647.60546875

So 21.58049011230469 is min. count and 33647.60546875 is max. count.

What are [46,3] and [20,9] before the counts? Definitely they are not x,y coordinates in my image section.

swapnil

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Mike Fitzpatrick wrote on Mar 19, 2009

They are the coords of the min/max pixel. However, suppose you have a 100x100 section of a 1024x1024 image, the coords will have a max value of 100 because the section size is only 100x100. Passing an image section into any task is very much like copying out that section to a new image first, in your case just add the task coords to the image section to get the coord in the parent image.

-Mike

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smp wrote on Mar 19, 2009

Thanks Mike.

I checked the co-ordiantes. They are right.

Now I am writing a small script , so that I can find x,y coordiantes of min. and max. counts for a specified image section in all my images:

procedure find_xy(input)

string input {prompt = "Name of file containing reduced images"}

begin

  string str

  minmax(images = input, force = no,update = no, verbose = no) | scan(str)

  print(str)

end

If I run this script , I get the error:

ERROR on line 13: Attempt to access undefined local variable `str'.
find_xy ()
find_xy ()

I have declared the 'str' as string .
What is the reason for such error?

Swapnil

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James Turner wrote on Mar 19, 2009

The cause of the error is that no value was placed in "str" by scan() because you ran minmax with verbose-, which doesn't print anything... Thus in the final print statement you are trying to print the value of an uninitialized variable.

Before using scan() to parse output from a command, it is always a good idea to run exactly the same command without the pipe first, to make sure it is doing what you think it should be.

Cheers,

James.

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Last post on Mar 19, 2009