Please explain "EMPTY MAGNIFICATION"

Joyful · Post by **Joyful** » Mon Dec 14, 2015 1:13 am

Good Morning folks -

I have just come against the term"EMPTY MAGNIFICATION", and wonder what it means in real life.

Please will SKS illustrate examples of this for me, as I may be suffering from it.

Thanks in advance

Joyful

rjlittlefield · Post by **rjlittlefield** » Mon Dec 14, 2015 1:34 am

I don't have an image handy, but here it is in words:

Real magnification: the subject looks bigger, and you see more detail.

Empty magnification: the subject looks bigger, but you do NOT see more detail.

Imagine taking an image that is 100x100 pixels, and blowing it up to 300x300 pixels. That would be empty magnification -- bigger but no more detail.

In an optical system, the amount of detail is always limited, by diffraction if nothing else. "Empty magnification" happens when the image is magnified beyond the point necessary for the viewer to see all the detail that the image contains.

--Rik

Joyful · Post by **Joyful** » Mon Dec 14, 2015 2:12 am

Thanks Rik - on the ball - as always !

Thanks for a very clear explanation. I get the 100x100 up to 300x300 story.

Does this image look like it has empty magnification in it ?

rjlittlefield · Post by **rjlittlefield** » Mon Dec 14, 2015 9:41 am

Joyful wrote:Does this image look like it has empty magnification in it ?

There is a simple test that I like to use:

1. Pull the image into Photoshop (or any similar tool).
2. Crop it to be an even number of pixels on each axis.
3. Make a copy.
4. Resize the copy to be 50% (shrunk to half size).
5. Resize the 50% copy by 200% (restoring it back to the original size).
6. Layer the shrunk/restored copy on top of the original.
7. Flash to compare.

Using this test, an image that clearly has empty magnification will look almost exactly the same after it has been shrunk and restored. That is one extreme case. At the other extreme, an image that clearly does not have empty magnification will look much different, with significant detail being completely lost in the shrink/restore. Between those two extremes there is a spectrum of variation.

When I apply this test to your image, here is what I see. (This animation has been blown up by 200% as an extra step 8, to make the comparison simpler to see.)

In this flash-to-compare, I can only find a few subject details that were completely lost in doing the shrink/restore. But there are lots of details whose contrast was cut so much that they would be simple to overlook in the shrunk/restored version, although they're obvious in the original. Those details would be effectively lost.

It's worth noting at this point that there is an unavoidable tradeoff between looking sharp and retaining all the details. A frighteningly long time ago, I summarized that tradeoff in an article titled "On the resolution and sharpness of digital images..."

In order for our digital image to "look sharp", we have to shoot it or render it at a resolution that virtually guarantees some of the detail in the optical image will be lost. If you see some tiny hairs just barely separated at one place in the digital image, it's a safe bet that there are quite similar tiny hairs at other places that did not get separated, just because they happened to line up differently with the pixels.

Conversely, in order to guarantee that all the detail in the optical image gets captured in the digital image, we have to shoot and render at a resolution that completely guarantees the digital image won't look sharp.

So, there's "sharp" and there's "detailed" -- pick one or the other 'cuz you can't have both. What a bummer!

So, I would say that your image is in the transition zone. It doesn't look sharp at the magnification that it's shown, but if it were magnified less, some detail would be lost.

There is much more discussion of that tradeoff, at the link listed above.

--Rik

Bushman.K · Post by **Bushman.K** » Mon Dec 14, 2015 12:16 pm

Joyful, there is another method, which is close to one rjlittlefield just suggested.
Using freeware GIMP editor and Wavelet decomposition plugin, you can split your image into several planes (layers), representing different size of details - 1px, 2px, 4px and so on. You can examine them individually by switching all other layers off.

First one (1px) can't be totally empty - it usually contains something even if the image is "overmagnified". Camera noise is always there, as well as subtle hints of edges. But turning and off against the Residuals layer helps to find out, if these details are valuable or not.

In case of your image, amount of finest (1px) details is significant, but fairly small.

Same method can also be used for detail enhancement and noise suppression, because changing the contrast of any layer and fusing them back together leads to sharpening/blurring details of corresponding size.

Joyful · Post by **Joyful** » Mon Dec 14, 2015 1:56 pm

Thanks Rik and Bushman.

May I send you the full file that I obtained from my stack of over 300 images so you can assess the image uncropped ? about 32 meg ? I will include full technical details.

PM or WeTransfer ?

Joyful

Bushman.K · Post by **Bushman.K** » Mon Dec 14, 2015 2:16 pm

Since email will not work due to file size, feel free to use any file sharing service such as Sendspace or DropBox, or whatever you like.

Olympusman · Post by **Olympusman** » Mon Dec 14, 2015 2:56 pm

Another manifestation of empty magnification is to use higher powered eyepieces. For the most part, 10X eyepieces are pretty much a standard ( Olympus NFKs are an exception having far more modest magnifications for use in photomicrography). So if you are using 15X or 20X eyepices, you are simply enlarging the image already provided by the condenser/objective combination. It is not that much different from shooting an image with a digital camera using digital zoom. Instead of using digital zoom, you would be far better off not using digital zoom and have a better original image which you can then post-process in a program such as Photoshop. Once you use digital zoom or higher powered eyepieces, there is no going back.
A great example of empty magnification is in advertisements for camcorders that offer 800X zoom, which is ludicrous. Not only is the digital magnification absurd, but I doubt there is a tripod anywhere on the planet that stabilize such a ridiculous feature.

Mike

Joyful · Post by **Joyful** » Tue Dec 15, 2015 1:34 am

Hi Bushman -

I have downloaded and installed Gimp with the Wavelet decompression plug-in, but then get stuck. I am totally new to Gimp. Please offer some guidance to a geriatric blonde, or tell her where she can get a downloadable manual so I can generate the layers you describe and view them individually. All I see is a grey screen.

Joyful Thanks in Anticipation

Joyful · Post by **Joyful** » Tue Dec 15, 2015 4:07 am

GETTING THERE - My version of Gimp had all the tools hidden, so I struggeled to see layers at all.

To recap - If I bring in an image, and can see nothing (just a grey screen) at level 1 does that indicate an out-of-focus image or what ?

Joyful New discoveries every day !

Bushman.K · Post by **Bushman.K** » Wed Dec 16, 2015 1:24 pm

Some sort of tutorial on this topic.

http://www.photomacrography.net/forum/v ... 540#181540