The digital zoom heresy (or Why a limit on digital zooms?)

[Lauren]

We all 'know' that digital zooms are useless. You're just taking an area of the CCD and blowing it up, the same as cropping it in Photoshop. Digital zoom just makes a part of the picture bigger without actually getting closer to the actual object.

So why don't we see 10x digital zooms? 100x digital zooms? If we are able to zoom in 4x digitally, what's to stop us from zooming in until we've got one pixel blown up to 2048x1680?

Digital zoom obviously doesn't simply mean 'cropped'. It means 'cropped and enlarged'. What kinds of in-camera image enhancements are we throwing away by disregarding digital zooms?

[Binji7]

Several cameras do just that, crop the image. Some on the other hand do interpolations - so you still get a larger image, but most of the data in it is 'guessed' by the camera - probably determined by the value of adjacent pixels.

Another reason why you don't get 100x zoom digicams is because of the final output medium. They would look HORRIBLE if I printed out a 8x10 with 10x Digital zoom, interpolated or not.

Look at the Video Camera segment - many have 400x zooms, but the final output medium is on a TV with a very low output res (less than VGA 640x480 I think).

It all depends on that final destination................

[Lauren]

I believe that NTSC is 640x240 and the vertical pixels are doubled. I've been known to lie, though.

[Gimli]

Originally Posted by Lauren

I believe that NTSC is 640x240 and the vertical pixels are doubled. I've been known to lie, though.

From some website

The NTSC standard has a fixed vertical resolution of 525 horizontal lines stacked on top of each other, with varying amounts of "lines" making up the horizontal resolution, depending on the electronics and formats involved.

PAL has 625 horizontal lines making up the vertical resolution

Now I thought, most TVs could only handle a 300 line of resolution signal. HDTV being just a little over 1000 lins of resolution...

Or am I wrong?

[voxmagna]

Actually this question is not as stupid as it seems, since I tried to get a similar debate going once before with few 'takers'.

Say you only need 6x4 prints at 300dpi. thats 2Mpix. If your cam is a 12Mpix cam or higher - why not digital zoom? Very compact. light and convenient and probably cheaper to make in future, than a big glass lens.

Where is the quality trade off point between more pixels, standard lens, less pixels in sensor and big glass zoom?

Now I thought, most TVs could only handle a 300 line of resolution signal. HDTV being just a little over 1000 lins of resolution...

Yes, although there are 625/525 lines, first they don't all carry picture, second the horizontal bandwidth is limited by what you can get coded over air and filter out, thirdly most TV's have a fairly coarse shadow mask or PIL mask tube. So the actual visual resolution is really close to 300 lines. Interlace throws in some nasty probs as well.

However, you can do a bit better with RGB/YUV or digital video and progressive scan. Put your cam pics out to a TV on RGB and see the difference! - still not up to a pc's SVGA though.

[normc]

We need more discussion on digital zooms and some input on the firmware used by camera producers. For example, does metering and focus occure before (on the entire CCD ) or after the digital zoom? I know digital zooms have preformed better on all of the Sony Cameras that I have owned compared to others also owned, so they are not ALL the same.

I think the comments made by the above writers are very good ones and deserve good answers. If digital zooms can be done better in an editing program we need to know why? If the answer to the metering and focus question is after the zoom then how would you do the same thing in an editing program?

[Lauren]

I think normc hit on exactly the stuff I was thinking about. Namely, perhaps we are actually missing out on some good stuff by pooh-poohing digital zoom.

We are all coming at this from an angle that forces us to consider the digicam as a black box. We can't tell what's going on in its head beyond what it shows us.

The way to prove this one way or the other would be to take two shots of a scene, one using digital zoom and another without. Crop the un-digizoomed pic and enlarge to match the digizoomed one. Compare, contrast, write a 2000 word essay on the analogies between the steam engine and the personal computer.

Any takers? (though I seem to recall in a previous discussion that this was already done and decided in favor of digital zoom...)

[voxmagna]

Any takers? (though I seem to recall in a previous discussion that this was already done and decided in favor of digital zoom...)

Yes I think you are right. The comparison test must be done on uncompressed RAW image files. Though I can't understand why in camera digizoom should be worse than in post editing. In post, you are often working on the compressed image, whereas in cam, it can be done before the jpeg compression. Somebody said editors and pc's are more sophistocated. So the question remains - what is the order of processing an image after capture and how is the in-cam zoom process different to editor software.

[NHL]

Well how big or powerful can an in-camera processor be? Usually to save both cost and power (ie running on battery) not the most powerful processor are used and after a 12-bit A/D conversion, the computation is usually round off to 8-bit, which is all that is needed for jpeg or tiff (ie 24-bit color).

A raw 12-bit capture can be input to Photoshop with the option of computing at 16-bit (with floating point from a Pentium, Opteron etc...). On top of that there's fractal programs as well as all kind of vendors competing for the quatlity of theses enlargements (ie digital zoom), unlike a one vendor(take it or leave it) camera only. :lol: :lol: :lol:

Definetly post-processing from the raw is better than in camera jpeg (or tiff)!!! 8) 8) 8)
... The problem is some camera just don't have raw output... ops: ops: ops:

[Mike_PEAT]

I actually turned off the digital zoom on my camera (then again I have a 10x OPTICAL zoom).

Anyway, the way I see it is I can do digital zoom on the computer better than I can do it on the camer with a lot more control!

Digital zoom distorts the picture...I want to get the best undistorted picture I can, and then I can distroy it after on the computer however I want; but at least I still have the original sharp and clear that I can always get back to. Using digital zoom you never have that.

Also, most digicam owners don't want to lug a tripod around (don't forget that even with digital zoom you are multiplying camera shake as well). One of the complaints from new megazoom owners is that their picture is blurry at the full 10x optical zoom...never mind if you added the 3x digital zoom on top of that to give 30x zoom.