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Message-ID:  <[log in to unmask]>
Date:         Tue, 12 Sep 2000 13:16:25 -0500
Reply-To:     ImageJ Interest Group <[log in to unmask]>
Sender:       ImageJ Interest Group <[log in to unmask]>
From:         Rex Couture <[log in to unmask]>
Subject:      Difficulty with contrast/brightness adj.

        A quick and easy way to do image registration is to copy a corner from one image and to paste it into the other image, using Paste Control to set the paste mode to "difference" (or maybe "subtract" or "blend").  The paste window is then moved around until the best location is found, and the location is noted.

        In practice, this may not work at all because of limitations in brightness and contrast adjustment.  Usually the values in the paste window are near zero (i.e. invisible), so the contrast and brightness must be adjusted.  Unfortunately, the B&C control does not operate at this point.  Even if it did, the range of adjustment seems to be limited by the image histogram *before* pasting.  For example, in working with 16-bit integer images, my typical image values lie between 2500 and 4000.  The values for the difference image may be less than 100, and are therefore displayed as black.

        Any suggestions?

Sincerely,

Rex Couture, Ph.D.
Dept. of Radiology
Washington University
Campus Box 8131
510 S. Kingshighway
St. Louis MO 63110
(314) 747 0332

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