Lossless digital zoom in digital cameras

These last two weeks I've been on my honeymoon holidays...really really nice. I have been quite disconnected from computing or technological news, but I learned a useful feature of my digital camera that was absolutely unknown to me: the lossless digital zoom. Let me explain a little bit...

I have had several digital cameras and many of them had digital zoom. As this nice article explains, the digital zoom makes the illusion of having a longer optical zoom by making larger a small part of the original image the optical zoom gets (through interpolation). The result is a softened image (with less definition), not so clear as a normal one and not very useful in general. That's why I always disabled the digital zoom of my cameras. But, these holidays I discovered a great trick some modern cameras use to be able to enhance your optical zoom with a special kind of digital zoom that has no degradation...Is that magic ? No, but it's amazing anyway.

The trick is called "Smart zoom" by Sony and "Safe zoom" by Canon, but it's implemented by other cameras and it's pretty simple to implement. If you have a camera with many megapixels but you make a picture with less resolution than the maximum, your camera can actually make a picture with the maximum resolution and then crop it to the small part you have selected (by zooming with the digital zoom). In other words, the camera traditionally has had to make a large image from the small part selected by the digital zoom, and it had to "invent" the information it didn't have by interpolation; but now, it doesn't have to "invent" this information, because it actually has them (just selecting a larger resolution for the image). This article explains it much better than me, so read it (specially the "Smart zoom" part). This special zoom has limitations, it only can work if the image resolution you select is smaller than the maximum and the factor of zoom without degradation is not unlimited (in my camera I can "only" double the optical zoom range when I select a 1600x1200 resolution)...but it's enough for me.

The technique is equivalent to make a picture with a maximum resolution with the optical zoom and crop it yourself at home to the size of image you really wanted from the beginning, but it has some advantages:
  • You don't need to do this process at home (the camera does it for you), so this saves your time
  • You save space in your camera, because what is saved is the cropped image, not the lareg one (at maximum resolution)
  • You can choose the composition of the picture while you do it (I prefer it)
So...I have enabled the digital zoom in my camera again, it's worth it.

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