Magnification

[esther31]

How do I know what magnification do I have?
I scanned my picture, the whole image size is 2464x3432 pixels. I cropped it to remove excess background to 1260x1260 pixels. Then I selected a 296x296 pixels and duplicate that to open in a separate window.

I need to know the magnification of that window. Does anybody know how to measure it?

Thanks!

[Stoyan Pavlov]

Scan a ruler at the same resolution and calculate the pixel size in the
corresponding units. Since you didn't scale the image, but just cropped it
the pixel size will be the same in all three images.



2013/3/25 esther31 <[hidden email]>

> How do I know what magnification do I have?
> I scanned my picture, the whole image size is 2464x3432 pixels. I cropped
> it
> to remove excess background to 1260x1260 pixels. Then I selected a 296x296
> pixels and duplicate that to open in a separate window.
>
> I need to know the magnification of that window. Does anybody know how to
> measure it?
>
> Thanks!
>
>
>
> --
> View this message in context:
> http://imagej.1557.n6.nabble.com/Magnification-tp5002384.html
> Sent from the ImageJ mailing list archive at Nabble.com.
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html
>

... [show rest of quote]

--
Dr. Stoyan P. Pavlov, MD, PhD
Departament of Anatomy, Histology and Embryology
Medical University "Prof. Dr. Paraskev Stoyanov", Varna
Prof. Marin Drinov Str.55
9002 Varna
 Bulgaria
Tel: +359 (0) 52 - 677 - 086
e-mail: [hidden email]

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html

[fmonson]

Now, the simple answer.
When you crop an image you do not change its magnification - if that is knowable - UNLESS you resize what is left.  Changing the resolution will not change the 'magnification' UNLESS the size of the image is altered in the process.  

The final magnification of 'John' may be different but all changes to the image of 'John' are relative.  John is not any bigger than he was when the image was captured, and unless you know the dimension of some object in the image that is left, the magnification will not be calculable.  

Processing of the type you have performed is usually applied to improve the image.  If you still have the original image, you can determine the 'new magnification' by comparing the dimensions of corresponding objects in the original and final images.

Cheers, again,

Fred

Frederick C. Monson, PhD
Technical Director
Center for Microanalysis and Imaging, Research and Training (CMIRT)
West Chester University of Pennsylvania
Schmucker Science South - Room SSS-024
MailDrop:  Geology-Astronomy
750 South Church Street
West Chester, PA, 19383
610-738-0437
[hidden email]

HomePage:  http://cmirt.wcupa.edu (with link to instrument Scheduler)


-----Original Message-----
From: ImageJ Interest Group [mailto:[hidden email]] On Behalf Of esther31
Sent: Monday, March 25, 2013 12:47 PM
To: [hidden email]
Subject: Magnification

How do I know what magnification do I have?
I scanned my picture, the whole image size is 2464x3432 pixels. I cropped it to remove excess background to 1260x1260 pixels. Then I selected a 296x296 pixels and duplicate that to open in a separate window.

I need to know the magnification of that window. Does anybody know how to measure it?

Thanks!



--
View this message in context: http://imagej.1557.n6.nabble.com/Magnification-tp5002384.html
Sent from the ImageJ mailing list archive at Nabble.com.

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html

[esther31]

Im sorry. I am still confuse.
I was scanning a slice of cake
So I know the size of the cake which is about 8 cm x 7 cm. I also have a ruler by the cake, which are both scanned. So I set my scale according to that ruler, and convert everything in mm... because I do not understand the concept of pixel.

I have that ruler with the cake and then did all of the cropping and duplicate with it. Attached is my pictures. Now, I put my image with the scale bar on my thesis and my advisor wants me to state the magnification of that image.

Thanks!

[Gabriel Landini]

Here is my take on this:
Magnification means how much bigger or smaller the image is compared to the
original object. That is OK if you only use a microscope, but gets confusing
when you use images (i.e. how bigger/smaller will they be shown/printed?).

As Stoyan suggested, scan a ruler and measure how big a pixel is (you can do a
spatial calibration within IJ with the scan of the ruler). Because you rarely
know at which size the image will eventually be shown or printed, the best
approach (others might differ) is to either:
a) add a calibration bar (there is a command for this) or
b) just give the size in calibrated units of the width of the photo and report
this in the legend (i.e. field width 54cm)

The advantage of a) is that you do not have to remember this size and still
have the bar if you choose to crop it or resize. The advantage of b) is that
you do not change the pixels of the image by drawing the bar. I think that you
can add the bar as an overlay, but not sure all programs might be able to show
it.

I always quote pixel size as well, because in images given in calibrated
units, you can't easily tell the resolution (amount of detail) of the image.
But that is a different story.

Hope it helps
Gabriel

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html

[Anderson, Charles (DNR)]

I agree with the previous responses that your image with the black calibration bar should be sufficient, BUT to satisfy your advisor:

Print your image exactly the size it will appear in your printed thesis.  Measure the black bar. If it is 20 mm on the printed image, then magnification is 20/5 = 4 X.  You might add to the caption, "Magnification is 4X on the printed thesis page."

Then delete the sentence before you submit your thesis for publication elsewhere.

-----Original Message-----
From: ImageJ Interest Group [mailto:[hidden email]] On Behalf Of esther31
Sent: Monday, March 25, 2013 2:26 PM
To: [hidden email]
Subject: Re: Magnification

Im sorry. I am still confuse.
I was scanning a slice of cake
So I know the size of the cake which is about 8 cm x 7 cm. I also have a ruler by the cake, which are both scanned. So I set my scale according to that ruler, and convert everything in mm... because I do not understand the concept of pixel.

I have that ruler with the cake and then did all of the cropping and duplicate with it. Attached is my pictures. Now, I put my image with the scale bar on my thesis and my advisor wants me to state the magnification of that image.

Thanks!

<http://imagej.1557.n6.nabble.com/file/n5002399/Regular_1_with_scale_bar.jpg>
<http://imagej.1557.n6.nabble.com/file/n5002399/Regular_1.jpg>



--
View this message in context: http://imagej.1557.n6.nabble.com/Magnification-tp5002384p5002399.html
Sent from the ImageJ mailing list archive at Nabble.com.

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html