Digital Zoom Discrepancy Between Tutorials
John, question about some images in the Digital Zoom Tutorial compared to images found in the PTZ Guide (Both excellent references, by the way) In the first you make a strong case for the irrelevancy of higher than single digit zoom factors. As an extreme example you show this highly pixelated crop and zoom (12X) of a 29MP image:
Then in the PTZ guide, while making a similar if less vitriolic point, you max out the digital zoom here to 12X on a 2.1MP camera:
To my eye, the first one is far more pixelated and has been zoomed far beyond the point of being helpful. The second picture on the other hand, while no Van Gogh, is just reaching the point of not being helpful, IMHO.
Yet, the first is from a 29M image and the second from a 2.1M image, one with less than 1/10 the pixels... How can it be?
Note: The quality difference seems so large that I assume I am misunderstanding something from the videos, or my math is wrong. That's ok by me. Also, I apologize if my cropping and sizing for the post has altered the perception of the images, I don't think it has; but use them only as a reference back to the actual videos to be safe.
I do, of course, have a theory that might explain it partially but first I want to make sure that I have the comparison framed correctly. Thanks!
One is done in gimp (the 29MP), the other in a VMS. How they report digital zoom levels might be different.
For example, the Axis one was shown on a much smaller frame than the Avigilon one.
Whose side are you on anyway? ;)
Yes, I know it's smaller, I actually had to digitally zoom it a bit more to normalize it with the Gimp one, thus even further degrading the Axis pic.
Fortunately we have no need for my speculative comparison since we have your more grounded one:
Gimp's digital zoom levels appear to be different then Axis's. For example, 12x on Gimp on a 29MP image zooms in a lot further / tighter than 12x on Axis HD.
Twice as far, by my estimate. And so I agree, the Gimp image appears zoomed in far more That could certainly be what I subconsciously picked-up on and good reason for the quality difference. That would satisfy me and I would be ready to accept it, case closed, if it weren't for this baffling (to me) picture:
Here's the thing, if Axis reported digital zoom levels differently than others why do these pictures match? Not only are they apparently between two different cameras mfrs. Axis and (Canon?*), but they also show that Axis' digital zoom is reported in line with the way their optical zoom is. Is Gimp zoom different than optical zoom or do you think Axis reports digital zoom differently over 4X?
You may be right in the video that "any camera has more than enough digital zoom", but you also contend multiply that 4x is more than enough, even for multi-megapixel cameras. And if you are right about the zoom reporting differences, then this would not apply at least to Axis cameras, (and whoever may have copied their way of reporting).
At the risk of speculation, Occam's razor suggests that maybe their was another click still left in the zoom range when the video was made?? (I know, I know, I'm ordering a Q1755 right now. ;)
*Correct me if wrong.
Ok. I figured it out, no speculation.
PTZ tutorial is fine.
The Axis camera zoom, both digital and optical, from the PTZ tutorial do actually match gimp. I scaled in gimp the wide opening Axis shot to 40x and then to 120x and the FOV's match up.
The reason that the digital zoom tutorial examples seem far more ridiculous, even though coming from higher resolution sources is simple:
You are (sometimes) only showing a fraction of the actual zoomed FOV on your monitor. Gimp is actually zooming correctly and reporting correctly, but unlike a VMS window, gimp makes the whole image window bigger with every zoom. But as you point out, you don't have a 3MP screen, so when you zoom much of the scene goes off the screen. Especially in the case of the 12X 29MP image. Which gives the illusion of extreme zooming. So you were right in saying that the two screenshots can't be compared, but the reason is that one is not displaying the whole zoomed FOV.
Would you agree that this is what is happening on a technical level, at least?
I thought you might, since I believe it's obvious if you watch the video, so I didn't include any screenshots or 'evidence'. Just trying to save space and time. But I do have them, and will provide them if your not fully convinced.
Also, I assume you are prepared to argue that it doesn't matter whether the whole FOV is showing, but first I wanted to make sure we are agreement about what technically is occuring.
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