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  • GNOME
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  • #412

Closed
Open
Created Jul 09, 2012 by Bugzilla@bugzilla-migration💬Reporter

Possible wrong Otsu (auto) threshold value for binarisation

Submitted by Vincent

Link to original bug (#679622)

Description

Created attachment 218327 Picture-test to compute Otsu Thresholding

Hello,

Gimp use the Otsu method to compute binarization threshold.

If you compute the auto-threshold for the attached picture with Gimp 2.8 (menu "Colors / Threshold - Auto" or "Couleurs / Seuil - Auto in french), Gimp find 185.

If you compute the auto-threshold for the attached picture with ImageJ (menu "Image / Adjust / Threshold - Otsu"), ImageJ find 195.

I think these two threshold (195 and 185) can be improved.

  • Gimp return the threshold "s1" for maximum (GREATER) histogram standard variation.
  • ImageJ return the threshold "s2" for maximum (GREATER OR EQUAL) histogram standard variation.

I think you must compute s1 and s2 and return s = ( s1 + s2 ) / 2

Otsu threshold must be ( 185 + 195 ) / 2 = 190 for the attached picture. Look at the histogram, it is the middle...

(In most cases, s1 = s2 = s...)

Best regards,

Vincent

Attachment 218327, "Picture-test to compute Otsu Thresholding":
Imagette_test_Otsu_8bits.tif

Version: 2.8.8

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