Posted by
Michael Schmid on
URL: http://imagej.273.s1.nabble.com/Fwd-screengraber-and-pixel-calibration-tp5001755p5001756.html
Hi Jose,
if the ImageJ panel is in the background, the operating system won't pass keyboard shortcuts like the one for capturing to ImageJ. You can put the IJ panel to the very bottom, to reduce the part of the image covered.
Better: use the keyboard shortcut of the operating system to capture the image (e.g. Print-Screen Button) and paste the Image to ImageJ thereafter (when it is in the foreground).
If the resolution of your camera is less than that of the screen (1600*1200), of course it would be better to have the capture window at 1:1 zoom. Then you have space for the IJ panel.
Calibration:
Your image is distorted, and also the vertical scale is not equal to the horizontal one.
Here are a few results that I got (last column is line angle)
170.843 0.559 at bottom
171.329 0.559
171.700 0.559
171.996 0.559
171.842 0.522
172.189 0.522
172.169 0.559 at top - periodicity is clearly longer than at bottom
173.145 -89.946 left side
173.390 -89.891
173.804 -89.946
173.893 -89.946
173.911 -89.946
173.999 -89.946 center - vertical periodicity is largest here
173.565 -89.767
173.464 -89.709
173.299 -89.709
173.433 -90 right side
So it means that the optics have slight barrel distortion and the grid was not exactly perpendicular to the optical axis.
If I find time I'll publish the plugin used on the ImageJ wiki.
Michael
________________________________________________________________
On Feb 13, 2013, at 13:35, Jose Guzman wrote:
> Hi everybody,
>
> I am trying to save live images with ImageJ by simply grabbing from the
> computer screen with Shift+Ctrl+G (see attachment)
>
> 1) Is it possible to acquire the image without the menu of ImageJ program?
>
> 2) I'm using a 25 x 25 um grid for calibration. I wondered if the
> calibration of 172 pixels per 25 um is correct (different measurements
> give me slightly different values).
>
> Thanks a lot in advance
>
> Jose
>
>
>
>
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