Does decreasing Image Size increase Sharpness?

Started Feb 10, 2013 | Discussions thread
bugzie
Senior MemberPosts: 1,527
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Re: Does decreasing Image Size increase Sharpness?
In reply to nkistrup, Feb 10, 2013

nkistrup wrote:

All other things being equal, does reducing the image size setting, increase the sharpness of pictures taken? Example: If your camera's top resolution is 3648 x 2736, and you cut down to 1600 x 1200 (in this case my computer's top monitor resolution), will the sharpness increase? Given that you take shots faster by dropping the image size.

Why this question? In another forum, someone mentioned that the Sony RX100 can take sharper images by dropping it image size from 20M to 10M.

But even if true, it only applies to taking JPGs, since RAW is always full size.

When we talk about sharpness, we talk about a number of different things. One is purely the resolving power of the lens and the sensor. The larger the image, the more detail we can see. If we blow up our 20mp image so we can see all the detail -- look at the image at 100% -- pixel for pixel, we're going to see more detail in it than our 10mp image. Some lenses resolve more detail than others. But they might not appear "sharp". The tiny detail might appear quite soft. Try it for yourself if you have some different lenses of the same focal length. Get a tripod, make conditions perfect and test the resolving power of each lens. I've experimented a little with this, and in my tests, the lens that resolved the most detail actually produced the softest results. But it gave me detail lacking in the shots taken with other lenses. Other lenses produced more "punchy" results but they resolved less detail. This has to do with issues such as micro contrast. A lens might appear "soft" compared to another but actually be resolving more detail.

Another kind of sharpness is the one you're talking about. The apparent sharpness attained by sharpening algorithms of the camera's software or the "sharpening" in post processing. If you like, this is false sharpness. This is smoke and mirrors sharpness. Digital sharpening routines that accentuate edges and make images look sharper. They are not really sharper and if we use too much we can actually destroy very fine detail. Now we talk about "output" sharpening. That is, we change the amount of sharpening, false sharpening, according to how the image is going to be output. An extremely large file full of very fine detail when printed quite small can end up looking very soft. If you reduce the size of the image, and apply some digital sharpening it can end up looking much sharper. We have to take into consideration how the image is to be viewed. Your 10mp file can look much sharper when viewed on a monitor than a 20mp file because the accentuation of the edges caused by digital sharpening is more apparent. The 20mp file doesn't look as sharp because the computer has to interpolate the image down to your screen size and that will soften the image because this blurs the edges slightly.

So, the question of whether to shoot at 10mp or 20mp… A 10mp file can indeed appear sharper in certain viewing conditions. But this is just smoke and mirrors. Shoot at 20mp. That will give you maximum detail. If you are going to be viewing this image on your computer, create a special version for this. Down sample the image and apply some output sharpening. Or leave it at 20mp and apply some more aggressive sharpening because it will soften when viewed at smaller sizes. Make a special version of the file for this because if you use this file for other purposes, this amount of sharpening may be too much. There's sharpening done by the camera's software, there's sharpening we apply in post processing, and there's output sharpening. Be conservative with the first two, but with the last we can be as aggressive as we like if we create a special version of the file for a specific purpose.

Shooting a 20mp camera at 10mp because it looks sharper on your computer monitor is kinda silly. Why limit yourself from the get-go? You can have your cake and eat it too. Shoot at maximum resolution and then create a version for viewing on your monitor. You have paid for a 20mp camera. At some point, you're going to get a cracking shot where you'll want every one of those mega pixels.

If you're questioning whether we really need such high-resolution cameras, I get the point. A lot of novices don't really need 24mp cameras. Especially when much lower resolution images can give you apparently snappier results. But if you're a little more serious with your photography, you might want the flexibility of having higher resolutions.

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