Sony Zone


828: Smart (?) Zoom

Digital Photo Myth #9A: Every Feature Name is Consistently Applied.
Digital Photo Myth #9B: Every Feature is a Good Thing.

By Peter iNova  
Design and photography by Peter iNova

With the V1 came a new concept. Sony engineers had cleverly figured out that digital zoom isn't always a benefit, so they created a "Smart Zoom" feature that limited the digital enlargement to the inverse of a smaller-than-full-frame's proportional size reduction. A half size frame could only receive a two times digital enlargement.

Digital zoom is the process of taking a smaller chunk--a crop, so to speak--of a full frame and blowing it up to the full frame size. Of course the new full frame is reduced in detail by the enlargement process. So performing a digital zoom on a full frame image will only degrade the final image. And since only a portion of the original chip capture has been expanded to fill the whole frame, no large benefit in file storage space is achieved, either. But wait, there's more...

A 5M image chip 2560 pixels wide when shot at 1.3M size transforms the chip image to a file exactly 1/4 of the surface area of the original, thus each dimension is exactly half. The native down-sampling improves the image considerably and the smaller file is pixel perfect.

It's so good, in fact, that if a digital zoom were added BEFORE the full frame was down-sampled into the smaller frame, some or all of the lost detail from the blow up would collapse back into the improved detail of the small file.

It's a variation on the math of "One times two, multiplied by 0.5 equals one."

So what Sony's engineers designed into the V1 was a form of Limited Digital Zoom that never allowed the zoom enlargement to exceed the inverse of the file size reduction. In the case of a 1.3M file with its 1280 pixel wide image, the original 2592 pixel wide original file was limited to a Smart Zoom enlargement of just double. (The V1 uses the new 5M size of 2592 x 1944 pixels compared to the 707/717's 5M size of 2560 x 1920 pixels. Ignore the 32 x 24 more pixels. They don't add any significant extra image area, but they do make it sound like Bigger = Better.)

At two power of digital zoom and a 50% reduction in the linear dimensions of a file, the two phenomena would cancel each other out. Such a Smart Zoom setting will be exactly and precisely the detail and quality of a straight half-size crop from the middle of a full frame. The Smart part comes from the fact that you can't OVER digital zoom and thus expand the image digitally larger than a simple crop. Detail is preserved up to the crop level and isn't allowed to cause large files with severely compromised, reduced detail.

If you shoot with the V1 and DO NOT use the full range of the digital zoom, some degree of down-sampling still occurs and the result will be more telephoto than the optical zoom lens's maximum while still retaining an improvement in detail. This is especially true for images gathered as VGA files. Those 640 x 480 pixel images are video size, and far sharper and more detailed than anything you've experienced from a live video camera. They're very useful for Internet images, appearing rather large on the web as you can see here.

Here's a VGA frame from the V1 that was shot at its "x11" setting with Smart Zoom switched on. The number means that from maximum wide angle, the camera is performing at 11 power greater than 34mm (its widest) making an image that is equal to a shot with a 374mm lens (if such a thing could be attached). The limiting factor is the VGA frame's size, but this image is as sharp and clear as one can expect from a VGA frame under the best of circumstances. Smart zoom has delivered the goods. We have a VGA image that ranks among the cleanest on record, and we have an extra long telephoto effect nearly three times the focal length of the optical zoom at the same time.

The V1's Smart Zoom with VGA maximizes at what Sony calls "x16" meaning "x4" from the optical zoom and up to x16 as four more power of enlargement kick in as Smart Zoom. At x16 the image quality is an exact match to a crop out of the full 5M frame. No more, no less. So shooting at maximum Smart Zoom is not the smartest way to use it.

When the 828 appeared, Smart Zoom followed. Turn that feature on and the image is digitally zoomed up to the inverse degree that the chosen file size is smaller than a full 8M frame. Technically, this should completely defeat the idea of Smart zoom, because it does NOT allow for less than full Smart Zoom to be applied to the image, no matter what smaller file size was chosen, so no improvement by down-sampling can occur.

Some folk have claimed that it works like a champ, but that is not the case. Seeing, in this case is believing. But as in so many things that balance evidence with belief, some people would rather believe than see. So let's remove the blinders and perform a test.

Below are rollover A/B images. Roll your mouse over the image to see the B version.

Which is sharper, more detailed, and certainly "Smarter?"

One of these was a VGA image that used Smart Zoom, the other is a VGA-size crop out of the center of an 8M image. There are microscopic differences in them and you are viewing both source images at 100% size with no scaling or color correction or anything other than cropping deeply into the 8M image.

For this view, the camera was set to 28mm equivalent, so the 8M image was quite wide angle. In fact, it was 5.1 times the width of what you see here.

The VGA shot was enlarged by 5.1 power, making it equivalent to about a 142mm tele lens. It is not possible to use Smart Zoom at an intermediate setting with the 828 camera, so with Smart Zoom on, you can't capture a full wide, 28mm perspective. Of course, switching it off couldn't be easier, so that isn't so bad, but unlike the V1, which CAN zoom from full wide to maximum digital tele in one continuous sweep, the 828 is not as zoom flexible.

From the same vantage point, it may come as no visual surprise to see how Smart Zoom works in full optical telephoto zoom:

Do you see what I see? Both shots are within a micro-trice of each other. The B image shows a small anomaly in one of the shadows dead center, and if you look carefully, this seems to be a phenomenon that recurs every 128 pixels. Some sort of pixel row and column effect.

Follow the horizontal pixel row from the wiggling shadow over to the balcony on the left and you can see its effect there, as well. It shows up on the wiggling of the chimney, too, in a vertical manner. It doesn't show up as a noticeable effect except with this sort of direct A/B comparison. Foliage and mountains don't call attention to it at all.

No, it's not heat. Heat doesn't show artifacts every exactly 128 pixels.

On very scrupulous inspection tiny noise differences seem to be present, and depending on the foliage of certain plants, detail contrast moves around a bit, but not more than one might expect from two back-to-back shots in either form.

Which is which?

(Answer at bottom.)

Answer Time

Which is which. In every case, the full-frame, 8M crop is A. B is the VGA frame with Smart Zoom applied. Its artifacts of pixel row dropping or doubling (what IS that?) causes straight line detail to "swim" in the tele overlay. Is that chimney doing the hula?

This is a form of artifact that produces false detail, and if you look carefully at the wide image, it can be seen there, too. Apparently the scaling engine in the 828 does not perfectly enlarge or reduce the 5.1X magnification factor used here. Perhaps the ever so slight image scale difference between 8M crop and Smart Zoom scaled images is tied to the compromised pixel rows and columns.

Smart Zoom has a low IQ. It prevents over-enlargement of the image by the digital zoom conversion process (the alternative, Precision Zoom does a straight 2X enlargement and CAN compromise image quality), but it ends up lowering image quality to that of a straight crop. As such its sole use is as an in-camera crop to the smaller file sizes that can use it.

I think of it as a neutral feature, not a smart one. One thing is for certain. Smart Zoom isn't going to the head of the class in the 828 the way it does in the compact V1.

More will be here as the Sony Zone pages evolve.


PS: As experience grows with these cameras, so will this review and the Sony eBook. Available now on the order page.

© 2004 Peter iNova. All rights reserved. Do not replicate or link to images without permission. All photos by Peter iNova unless attributed to others. Photos are the copyright of their originators.