Re: Please help to point us to the right direction with ImageJ

[Qu, Tanxia]

Hello,

We are trying to use ImageJ to:
1. auto detect the center of the circle
2. measure distance of the four edges to center

The original tif image is 2MB. The sample is a pdf print but renamed to a txt file to be allowed for attachment.

We are new to ImageJ. Any help is greatly appreciated.

Tanxia
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[Michael Schmid]

Hi Tanxia,

here is a simple, though not super-accurate method:

(1) Auto threshold
(2) with the Wand, click the center, to select the thresholded square
(3) Crop
(4) Find Maxima with a tolerance of about 30 and 'exclude edge maxima'

The coordinates of the selected point roughly give you the position of the circle. Given the image size of the cropped image, it is easy to calculate the distance to the edges of the image.

For slightly better accuracy:
If all your circles have the same size (in pixels), you can construct a prototype circle and use the Feature Finder plugin to find it.
  http://imagejdocu.tudor.lu/doku.php?id=plugin:analysis:feature_finder:start

Michael
________________________________________________________________
On Sep 23, 2014, at 21:49, Qu, Tanxia wrote:

> Hello,
>
> We are trying to use ImageJ to:
> 1. auto detect the center of the circle
> 2. measure distance of the four edges to center
>
> The original tif image is 2MB. The sample is a pdf print but renamed to a txt file to be allowed for attachment.
>
> We are new to ImageJ. Any help is greatly appreciated.
>
> Tanxia

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ImageJ mailing list: http://imagej.nih.gov/ij/list.html