Edit: This is a backdated post, backdated by about 4 years, to the time when I bought my first camera and took my first few steps into photography.
1) Digital Zoom should not be used.
2) Digital zoom spoils image quality.
3) A camera should not be judged by the amount of digital zoom that it offers.
These are the claims and instructions that one will find all over the internet, preached by professional photographers and enterprises. Is this real or just a myth?
I have been bitten by the digital photography bug and bought my first digital camera one year back with the same points in mind. I have refrained from using digital zoom as much as possible. What are my views on the points mentioned above?
Digital Zoom is not evil. Yes, the 3rd point makes a lot of sense. As much as possible don’t judge a camera by the amount of digital zoom. Compare with respect to optical zoom and then use digital zoom as the comparison when zoom is the main criteria for purchase. If you find a camera with 4x optical zoom, no doubt prefer it over one with 3x optical zoom. But when you have two cameras with 3x optical zoom and one has 4x digital zoom and the other 6x digital zoom, then without a question of doubt the 6x is the one that will find its way into my pocket. The reason? Lets see what is digital zoom and why people are against it.
Digital zoom is not a true zoom. Why? Optical zoom uses a combination of lenses to magnify the subject and duplicate the image in question over the entire area of the sensor. Whereas in digital zoom, the image is taken with the maximum possible optical zoom and then a small area is cropped from this and enlarged to fit the full frame size. (The megapixel size of the original image) i.e Suppose you have an image of full frame size 2560x1920 and you use 4x digital zoom. Now the 4 time magnified part of the full image will be 2560/4 x 1920/4 = 640 x 480. So a portion of the image that is sized 640x480 is cropped and enlarged to 2560x1920. What this means is that lots of extra pixel information is added to the image and even with the best resizing/re-sampling algorithm, some detail is lost and the picture will look jagged and bad. So what the advantage of digital zoom?
The advantage lies in the use of digital zoom. Consider a huge white background with a small dark object in the center. The dark object is not necessarily black but is in fact (say) dark blue with dark green and brown spots. Suppose, this image at full optical zoom still doesn’t enlarge the image to full frame and covers only about 1/10th of the frame. Now the camera metering ‘sees’ a lot of white and assumes this as only a black object. When you see your final picture the details on the small object is lost, maybe not completely, but at least it doesn’t reproduce the vividness of the actual colors. This is because the dynamic range of cameras is smaller than what the eye can see and to accommodate the amount of white information a little compensation is made with regards to the smaller objects. The sensor doesn’t know that the object is the most important part of the scene and compromises a little with its detail. This problem can be alleviated a little using spot metering which will meter only on the center portion of the frame so that the object is marked as the important part of the picture and some colors are now reproduced correctly. But what if the object is so small that even spot metering is not enough? In this case digital zoom comes to the rescue.
When I zoom completely into the object, there are the following advantages.
1) I am able to see the point of interest more clearly and can frame it better in the viewfinder/LCD.
2) Since the object occupies a larger portion of the viewfinder, the camera can meter it better and can help reproduce much of the dynamic range.
The result? A much better reproduced picture. But it will be distorted because it is blow up. So what? Resize it back to the smaller size from which it was cropped. In the above example it is 640x480. Now downsizing also causes losses and some may argue that again the point of digital zoom was lost, but it is not so. Downsizing is much less lossy than expanding. Moreover, take the image in RAW mode and use the same re-sampling/resizing algorithm to downsize the zoomed image as the algorithm that was used to expand it. This causes very low pixel loss and the best part is that you have a well metered and reproduced image. So what if you can take only a small print? At least you have a print of that interesting object that you can show off to your friends with a similarly specified cam and lesser digital zoom.
Disclaimer: There are many many more considerations that you have to consider before comparing digital zoom and it also depends on the users preference. Some may prefer the feel of one camera and that may be a deciding factor. Some may like the twistable screen of a cam and weigh that over the higher digital zoom of another. The bottom line is that keep digital zoom out of the mind till every other required feature is found and still further narrowing of choice is required.
Of course when you have the money then you would buy a camera with larger optical zoom or bigger lenses in the case of SLRs. But not all are so fortunate like the pro photographers and monetarily blessed to afford such large lenses and ultra zoom cameras. In this case I would say there is no other choice than to go for digital zoom.
Zooming is also a foolish option when you can get closer to the subject. Move in as much as possible and then use optical zoom to get a shot, if that is also not good enough then go digital.
Inspiration: I was out birding this morning and there was a huge lake with a small bird sitting on a stick in the middle of the lack which was inaccessible to me. I was on the periphery and almost on the verge of falling over. I had a 400mm lens and spot metering on, but even this was not enough for a good shot. The water reflections and the dark coloring of the bird were both counter-productive to a good shot and I had to zoom in digitally. The shot was much better than the completely optically zoomed shot since I now had only the bird in focus and it was well metered because the bird filled almost 2/3rd of my frame. As I came back home I thought well and hard about how useful digital zoom was to my trip and then decided to write down this article.
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