Digital zoom vs resolution, especially for movies

[stickwolf]

Playing around with my Canon S3 settings... I got into thinking how sensible it is that the movie mode automatically has digital zoom enabled. I started to think "hey, since it is only 640x480, the digital zoom could just crop to a smaller part of the sensor, so it could be a true 48x zoom at that resolution!! Then I tried it and I was wrong. How disappointing!

It would seem totally simple and logical for zooming past optical at any resolution less than full to start cropping instead of blowing up the pixels. It sucks that I don't get that. Do any cameras actually work that way?

I used to think of digital zoom as useless because I could always just crop and blow up a full-res picture. But if I already wanted a lower-res picture, it would seem simple enough to have a feature that basically used the whole sensor and auto-cropped to the lower-res. Result would be identical to full-res cropped, instead of current result which is like a low-res cropped even more and then blown up back to original low-res size.

And for movies it would be the same issue, but even more substantially useful because there's no way to take a 6MP per frame movie and then crop later, so if this feature were added, I'd literally have 48x optical movie zoom. There's no possible workaround with the same results.

For pics, this would be a nice shortcut that saved memory, and I wouldn't really use it or care because I can always do the time-consuming version of shooting all my pics at full-res and then cropping. But for movies... jeez. Why didn't they design it this way? Any comments?

[SpecialK]

You lost me after the first paragraph.

If you just crop the image, you get a smaller image. You must enlarge it to get a zoom effect.

[stickwolf]

Ok, let me add visual aids:

Pretend this is the largest resolution file your terrible camera can take and this is max optical zoom
24583

There is no way without getting closer to get just the flower and still have a full resolution sharp image.

But, if you wanted a SMALLER image of just the flower, you could either crop smaller in post, or digitally zoom while shooting and then compress down to smaller size in post. Either way, this is the result:
24585

If you set the camera to a smaller image size while shooting you will have no way to get the above image. If you crop the small image in post and then blow up back to the small size that will look identical to digitally zooming to the flower while shooting. Having the camera save smaller resolution files, you will never be able to get the detail of the above crop. Instead, the result will be this:
24584

That is terrible. But the camera was all set to take enough data to get the better image above. So if a camera were designed better, then on any setting below full resolution it would start cropping from full res instead of zooming the already shrunk image. Digital zoom would then be basically an automatic short-cut version of cropping a full res image. This would NOT work for saving full res files. So it would have no impact on someone like me who always shoots full res anyway, except maybe providing a convenient way to kinda auto-crop while shooting.

BUT... for MOVIE modes!! Movie mode on my S3 is max at 640x480. If digital zoom on movies behaved like my hypothetical auto-crop, then I'd have TRUE 48x zoom while shooting movies with no resolution loss!!! The cropping from full resolution sensor would be like an added optical zoom aspect. I'm assuming the restriction to 640x480 is based on memory and buffer being limited for 30fps images, but the sensor could still operate at full resolution. So I'm suggesting the camera could handle movie data by throwing out the outer section of the sensor while saving instead of applying digital zoom to images that have already taken the full sensor output and squished to 640x480. This would occur when zooming past normal optical zoom. There is no reason this couldn't be done. I'd gladly take the noise of a 100% full res crop over the blurriness of digital zoom.

I know for a fact that cameras like the Panasonic DMC-TZ3 have larger than necessary sensors and simply use less than full sensor in order to have wide-angle at all resolutions or something. If the use or not of full or partial sensor could be changed by camera settings while in use, then my concept would work. Look at the difference above. Why in the heck don't they do things this way??

[stickwolf]

To be absolutely clear in a summary:

For anytime saving smaller than full size images (including while shooting movies), why doesn't "digital zoom" crop from full size before saving instead of enlarging files after they are saved small?

[timmciglobal]

...

You even lost me.

FILE SIZE has nothing to do with ZOOM. Digital zoom DOES crop and resample the EXACT same way you would CROP using the "full image".

As far as video goes there is no camera that can read enough of the sensors data off fast enough to get 30 FPS at 6 megapixels and while your right it would make sense if they could pixel map 640x480 from middle of sensor as far as I know it's not yet been implimented.

Tim

[stickwolf]

...

You even lost me.

FILE SIZE has nothing to do with ZOOM. Digital zoom DOES crop and resample the EXACT same way you would CROP using the "full image".


Oh yeah?!? Try setting your camera to a small resolution, then digitally zoom in and take the shot. Then take a full res shot and crop it later on your computer. Is the result exactly the same? I think not.


...
As far as video goes there is no camera that can read enough of the sensors data off fast enough to get 30 FPS at 6 megapixels and while your right it would make sense if they could pixel map 640x480 from middle of sensor as far as I know it's not yet been implimented.

Tim

Yeah, that's what I'm talking about! Since it has a 6MP sensor, and since the movie is limited already to 640x480, then if they could pixel map from the middle of the sensor it'd result in true 48x zoom for the otherwise identical specs of my S3... well, assuming they could have a smooth transition range controllable all the way from full sensor to 640x480 in the middle. All the while, whatever portion of the sensor was being used, the movie would just be saved at 640x480. Anyway, result would be essentially true 48x optical zoom for a 640x480 movie. That'd be a reasonable feature to market for a camera. And a larger MP camera could do the same for even larger movie resolutions.

[timmciglobal]

Stick: SMALL is the number of PIXELS SAVED and as such "small" naturally results in LESS quality when then using digital zoom feature....

SMALL has nothing to do with "zoom" it's simply the ammount of base pixels to "Start" with and less pixels = less detail. If you "crop" a 4000x3000 image you have a portion of that, if you do the SAME with a 2000x1500 image you have LESS detail once the crop is done.

With memory prices where they are no reason to use < large unless you have no intention of printing/croping and posting just directly to web.

Tim

[stickwolf]

Yeah, but for movies...!

Anyway, I'm still right about the results of combining digital zoom with small file size. It is worse than cropping from large file size. And since the only purposes of small file size are convenience and memory saving, the sensor portion zoom that I'm suggesting would achieve those same goals with better results! But you're right that cropping full size later is the way to go, and just get a large memory card. And yet that point doesn't make the facts I'm saying irrelevant or untrue.

An amateur P&S shooter carelessly setting a low file size and using digital zoom would benefit from my solution. And if one should never use those features, then they should eliminate them from cameras, or they should improve them as I suggest.

And who wouldn't appreciate true 48x zoom for movies?

[Visual Reality]

I see what you are saying. Cropping from full-size surely gives a better picture. The problem is, the camera is simply not powerful enough to do that amount of processing in real-time. It just cannot capture 30 frames per second at high resolution, and process them, with sound.

However, you propose that not the entire sensor is used, to get a 640x480 file that doesn't need said cropping. I'm having trouble understanding how you are getting 48x zoom though. If you only use a 640x480 portion of the sensor you get the same thing as cropping a 640x480 area out of the image. It isn't zoomed, and its the same size as it was before. It is just cropped out.

Maybe that is what you are getting that. You can have, in movie mode, a cropped portion of the screen that is essentially at the same "zoom" as a full-size image, only in 640x480 pixels, as opposed to the full size image shrunk down to 640x480. Then at that point, you start your zoom. Well, you still end up with a max 12x zoom, now its just really small.

I don't see how its that beneficial.

[stickwolf]

Ok, I'll try to explain again... obviously SOME things are getting across.

What if the FULL sensor were used just like it is now almost all the time... then after 12x optical zoom (still using full sensor), the camera had a further zoom that was accomplished by progressively shrinking the portion of the sensor used. In other words, enable that AFTER reaching full tele zoom normally. If it could happen smoothly from full sensor down to 640x480 it would be at least another 4x zoom.

To explain further, the camera would behave to the user exactly as it does now. It would be STUPID to enable this extra sort of zooming before using up the normal 12x optical zoom. And accordingly, the camera I have in my hands uses optical zoom and only enables digital zoom when optical zoom is used up.

The difference I'm suggesting is that when digital zoom enables (again this means past 12x optical), it STARTS to use less and less of the sensor instead of digitally zooming the full sensor's output that has already been compressed to the 640x480 resolution.

So anyway, if it did exactly what you seem to understand, but it enabled it progressively after 12x optical zoom was first reached, then it would be effectively 48x+ zoom.

To clarify further, there is one problem with Visual's post: if the camera were identical and simply always used only the middle sensor, then we would indeed have only 12x zoom... but it would no longer be 36-432 equivalent, it would be something like 144-1728 equivalent. That's because it would be showing a smaller portion of the lens's input. So my suggestion is to have 36-432 equivalent happen as normal and then start shrinking the sensor use to result in up to 1728 equivalent. Doesn't that sound pretty awesome?

[stickwolf]

I just read the new Canon S5 review, and low and behold, my idea exists... they call it "safety zoom." I mean, I think it basically functions comparably. And Jeff even mentions that some other cameras have it as well. The only real question now is whether it is available in movie mode... he didn't mention that. Anybody know? At any rate, it looks like the future will be this idea implemented pretty universally, since it certainly is simple enough (despire the naysayers here who somehow feel that if an improvement is minor and not exciting then it isn't even worth implementing).

[David Metsky]

It works in still mode only when you reduce the image resolution. It's really not any different functionally from normal digital zoom, all it is doing is putting a warning and a hard stop in place to prevent loss of quality. There's no new functionality here involving using a smaller part of the CCD, as far as I can tell. So this isn't what you have been describing.

[Graystar]

I just read the new Canon S5 review, and low and behold, my idea exists... they call it "safety zoom." I mean, I think it basically functions comparably. And Jeff even mentions that some other cameras have it as well. The only real question now is whether it is available in movie mode... he didn't mention that. Anybody know?

Safety Zoom was announced in August ?06 with the new A series cameras (630, 640, and 710.) I believe all cameras introduced since then have it. The Safety Zoom feature is NOT available in movie mode on my A710, and I don?t believe it?s available on any other camera?s movie mode. The TX1 might be different. You?d have to check the specs.

It?s a nice feature. I just don?t think there?s enough horsepower in the camera to apply it during movies.


It's really not any different functionally from normal digital zoom, all it is doing is putting a warning and a hard stop in place to prevent loss of quality. There's no new functionality here involving using a smaller part of the CCD, as far as I can tell.

Actually, that?s exactly what Safety Zoom does.

The hard stop is there whether or not Safety Zoom is engaged. The hard stop simply signals the end of optical zoom.

Safety Zoom is also used with the digital teleconverter. So if you set your digital tele to 1.5X, and your resolution is set below the maximum, the camera will crop instead.

On my A710, when in safety zoom the zoom bar will be yellow. Beyond that you?re in deteriorative zoom and the zoom bar is blue. With digital teleconverter, the ?T? is white when safety zoom is engage and blue when in the deteriorative zoom range.
________
Mercedes-Benz 500E Specifications (http://www.mercedes-wiki.com/wiki/Mercedes-Benz_500E)

[stickwolf]

Safety Zoom was announced in August ‘06 with the new A series cameras (630, 640, and 710.) I believe all cameras introduced since then have it. The Safety Zoom feature is NOT available in movie mode on my A710, and I don’t believe it’s available on any other camera’s movie mode. The TX1 might be different. You’d have to check the specs.

It’s a nice feature. I just don’t think there’s enough horsepower in the camera to apply it during movies.


Right, but it's optical quality issues that are generally the limiting factor, so hopefully we can expect to see this for movies when the computer chips in the cameras get faster. For movies, this feature would be really useful, since (as I've been saying) movies are always lower resolution than the CCD offers for stills.



Actually, that’s exactly what Safety Zoom does.

The hard stop is there whether or not Safety Zoom is engaged. The hard stop simply signals the end of optical zoom.

Safety Zoom is also used with the digital teleconverter. So if you set your digital tele to 1.5X, and your resolution is set below the maximum, the camera will crop instead.

On my A710, when in safety zoom the zoom bar will be yellow. Beyond that you’re in deteriorative zoom and the zoom bar is blue. With digital teleconverter, the “T” is white when safety zoom is engage and blue when in the deteriorative zoom range.

Right. What else would "prevent loss of quality" mean? It certainly appears to be totally different than normal digital zoom. Otherwise it would be a very stupid gimmick if the whole point was that it just decided for you how much digital zoom was too much. I expect it certainly does use a smaller portion of the sensor. They don't process it that way though, they probably buffer a full-res image and instantly crop it for you digitally. And that's the reason it couldn't be done for movies, because it requires buffering the whole full-res image. So we still have yet to see something that would dynamically work quite as I hope, but this is the right idea.

-Aaron

[David Metsky]

Are you sure that's how it's implemented? I thought it simply judged where you could see the loss of image quality and stopped it there. In full image size, that means no digital zoom because it's noticeable right away. If you reduce the image size to 3MP you can get away with more digital zoom because it's not otherwise noticeable.

But I think you are getting the exact same pixels you'd get if you shot a full frame image and then cropped. I haven't seen evidence the camera is doing any additional processing that I couldn't do with a straight crop tool. It's a convenience so you don't have to crop yourself and prevents you from using too much digital zoom, but AFAICT, that's it.

[griptape]

So here's my opinion. GO BUY A CAMCORDER! Most point and shoots you can't even use the optical zoom. You want something that can give you the zoom of a camcorder, go buy one.

[stickwolf]

Are you sure that's how it's implemented? I thought it simply judged where you could see the loss of image quality and stopped it there. In full image size, that means no digital zoom because it's noticeable right away. If you reduce the image size to 3MP you can get away with more digital zoom because it's not otherwise noticeable.

But I think you are getting the exact same pixels you'd get if you shot a full frame image and then cropped. I haven't seen evidence the camera is doing any additional processing that I couldn't do with a straight crop tool. It's a convenience so you don't have to crop yourself and prevents you from using too much digital zoom, but AFAICT, that's it.

We are agreeing on the result. The result is equal to shooting full frame and then cropping as done with any software. And as such, it is just a convenience.



So here's my opinion. GO BUY A CAMCORDER! Most point and shoots you can't even use the optical zoom. You want something that can give you the zoom of a camcorder, go buy one.


Fair enough. But that doesn't mean my idea doesn't make sense. And it sure is obvious by the marketing and new products being designed that I'm not alone in being interested in a truly quality multifunction photo/video device. And the first company that uses my idea and can offer a 40x+ zoom capable video recording in a point-and-shoot digital camera with high quality manual controls.. that will sell a LOT, I'm certain of it.

[griptape]

Your idea is admittedly a nice thought, but it has no grounding in reality. For the same reason that digital cameras can't produce the same image quality as a dedicated camcorder, camcorders can't produce the same image quality still pictures. They're two completely different sensor technologies. Far more practical than your idea would be just to put two different lenses and sensors in the same camera.

[stickwolf]

Your idea is admittedly a nice thought, but it has no grounding in reality. For the same reason that digital cameras can't produce the same image quality as a dedicated camcorder, camcorders can't produce the same image quality still pictures. They're two completely different sensor technologies. Far more practical than your idea would be just to put two different lenses and sensors in the same camera.

I didn't realize the sensor technology was different. But for less than pro level usage, there's certainly nothing wrong with using the same LENSES.

[David Metsky]

The problem is that you're expecting the cameras to use only part of the CCD when capturing the image, right? Use only a section that corresponds to 640x480 in the center of the CCD for full zoom, is that correct?

Because right now sensors can't do that. You get the entire image that falls on the sensor and then the electronics come along and create the image that gets stored to disk. It's not set up to take part of the image at a time, you get it all, then they're potted down to 640x480 or whatever. It's the same when shooting at less them max resolution in still mode. The camera takes the entire sensor image and then pots it down to whatever you have set.

It would be an interesting enhancement to the technology, but I don't think it's simple.

[Graystar]

Are you sure that's how it's implemented?

Actually, no. As far as the hard stop is concerned, your description is correct. You can zoom through the optical zoom and into digital zoom without stopping as long as you remain in the non-deteriorative region. I could have sworn my camera was stopping at the end of optical zoom regardless of the resolution, but that wasn't the case.

That said, lots of testing has demonstrated that you get the same exact results from a 640 x 480 center crop of a full resolution, full zoom image as you do from a 24X zoom in 640 x 480 resolution.
________
TOYOTA SA HISTORY (http://www.toyota-wiki.com/wiki/Toyota_SA)

[stickwolf]

That said, lots of testing has demonstrated that you get the same exact results from a 640 x 480 center crop of a full resolution, full zoom image as you do from a 24X zoom in 640 x 480 resolution.

But that's only if they have a feature like this new safety zoom, however they implement it. At any rate, he real suggestion that I most am saying is that if this safety zoom could work for movies, that'd be great, since you can't record movies at full resolution on any of these sorts of cameras, even stuff like the TX1. So if they made a camera with processing power strong enough to do safety zoom during a movie... well, the question would be: would that power automatically be enough to actually record a movie at full resolution? If so, then I guess my suggestion wouldn't matter much. Except for storage issues, so maybe still...

I was hypothesizing a way to do a movie safety-zoom without insane processing power or memory issues. But overall, the new safety zoom feature of the S5 is truly the effect that I was talking about, just unfortunately not available for movies.

[Visual Reality]

It would require being able to save up to 8mp images at 30 frames per second. Currently the camera can only do between 1 and 2. They have a long way to go.

[John_Reed]

I posted Panasonic's explanation of their "Extended Zoom" (EZ) feature a couple of years ago, as it applied to the FZ30, which I'm still using:

http://john-reed.smugmug.com/photos/36041959-L.jpg

Key points about EZ "cropping:" Unlike digital zoom, the EZ cropped shot, once taken, is NOT interpolated back to the camera's full image size, it REMAINS at the cropped size.

Example: If I shot a full-sized image with my FZ30, i.e., 3264 x 2448 pixels, I'd get that size image from the camera, obviously. If I shot a 5MP EZ image with the camera, I'd get a 2560 x 1920 image. The functional differences for the camera are that in the full res mode, the zoom range is 12X, i.e., 35-420mm, whereas in the 5MP EZ range, the zoom range is 35-535mm. On the other hand, using digital zoom, the 5MP "crop" would amount to a 27.5% "Digital zoom" level. So at full zoom, the camera would take that 2560 X 1920 image it captured from the crop, and interpolate it back to 3264 x 2448 pixels to store an 8MP image. This is where the DZ "softness" enters in, through this process of interpolation to a larger size.

Benefits of EZ? Many people, including reviewers, think it's a waste of time, but those of us who use it a lot like it a lot. For one thing, viewing the cropped image gives you a closer look at your distant subject (we bird photogs refer to this as "subject intimacy") as you're framing the shot. Secondly, metering is improved on distant subjects, as you're getting more of the intended subject, less of superfluous surroundings, and finally, the images are smaller, so file sizes are smaller, burst rates are faster, etc.