Fwd: screengraber and pixel calibration

[Jose Guzman-2]

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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[Michael Schmid]

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
>
>
>
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html
> <Screenshort.jpeg>

... [show rest of quote]

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[Alan Hewat]

> use the keyboard shortcut of the operating system to capture the image (e.g. Print-Screen Button)

Yes. In MS Windows Alt+PrtSc captures just the active window (image).

> If I find time I'll publish the plugin used on the ImageJ wiki.

Do you mean:
http://biocomp.cnb.uam.es/~iarganda/SplineDeformationGenerator/ ?

> So it means that the optics have slight barrel distortion and the grid was not exactly perpendicular to the optical axis.
______________________________________________
Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
<[hidden email]> +33.476.98.41.68
        http://www.NeutronOptics.com/hewat
______________________________________________

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[Michael Schmid]

Hi Alan,

the plugin I was talking about is for measurement of periodicity along a line - an old version is here:
https://list.nih.gov/cgi-bin/wa.exe?A2=ind0703&L=IMAGEJ&P=R18654

Beware of lines truncated by the mailing list!

Michael
________________________________________________________________
On Feb 13, 2013, at 14:38, Alan Hewat wrote:

>> use the keyboard shortcut of the operating system to capture the image (e.g. Print-Screen Button)
>
> Yes. In MS Windows Alt+PrtSc captures just the active window (image).
>
>> If I find time I'll publish the plugin used on the ImageJ wiki.
>
> Do you mean:
> http://biocomp.cnb.uam.es/~iarganda/SplineDeformationGenerator/ ?
>
>> So it means that the optics have slight barrel distortion and the grid was not exactly perpendicular to the optical axis.
> ______________________________________________
> Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE
> <[hidden email]> +33.476.98.41.68
>        http://www.NeutronOptics.com/hewat
> ______________________________________________
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html

... [show rest of quote]

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[Cammer, Michael]

run("Close All");
for(i=0; i<10; i++) {
   run("Capture Screen");
   wait(500);  // wait half a second
}
run("Images to Stack", "method=[Copy (center)] name=Stack title=[] use");

________________________________________________________
Michael Cammer, Assistant Research Scientist
Skirball Institute of Biomolecular Medicine
Lab: [phone]  Cell: [phone]

-----Original Message-----
From: ImageJ Interest Group [mailto:[hidden email]] On Behalf Of Jose Guzman
Sent: Wednesday, February 13, 2013 7:35 AM
To: [hidden email]
Subject: Fwd: screengraber and pixel calibration

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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