thresholding bug?

[Neil Fazel]

I have two thresholded text images on which I am using the Wand Tool to draw contours. Both images are thresholded between 30 and the maximum value. I noticed that the Wand Tool contours on one of the images hugs the thresholded region (as expected), but on the other one is several pixels inside the thresholded region.

I tried to find out the reason, and it seems that in the latter case, the thresholded region (the red region) is displayed larger than it should be (by a few pixels). Looking at the pixel values I have verified that the Wand Tool contour is drawn correctly, i.e. it passes between pixel having values smaller and greater than the threshold value (30).

I have attached the two images side by side. On the left-hand side, the Wand Tool contour and the thresholded region basically coincide. On the right-hand side, the contour is inside the thresholded image. It seems to me, based on the correctness of the Wand Tool contour in both cases, that for the image on the right-hand side, the thresholding itself is correct, but there might be something going on with the the way it is displayed (i.e. the red pixels)

Here's a Dropbox link to the text image on the right-hand side.

https://www.dropbox.com/s/a61uzdrne2fdg0v/8351%20MS%201%202%20S4K%20-%20PSL%20-%20filters%20%26%20fiducials%20removed%20-%20600%20x%20600%20-%20INNMA%20h7%2Cv45.txt

Thanks,
Neil


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