downsampling reduces noice! - uh noise! - con't.

Started Nov 16, 2011 | Discussions thread
Great Bustard Forum Pro • Posts: 45,199
Downsampling vs noise reduction

John Sheehy wrote:

Associating downsampling or blurring with noise reduction will cause nothing but misconception.

Absolutely. However, a downsampled or blurred photo will appear less noisy when displayed at the same size. For example, if you downsample a photo, then upsample it to the original size, you have removed all the high-frequency noise and detail.

As I said and demonstrated a while back:

http://forums.dpreview.com/forums/read.asp?forum=1018&message=35068712

To that end, let's consider the following samples:

Does it really make sense to call the 50D pics "more noisy"? Or, instead, does it make more sense to say the noise is basically the same, but the 40D pics are simply "more blurry"?

In my estimation, the latter description seems to more accurately represent the images.

In another striking comparison, see what the difference is between downsampling and actual noise reduction:

http://forums.dpreview.com/forums/read.asp?forum=1018&message=37714016

The original crop:

Downsampled then upsampled:

Filtered with Noise Ninja:

It could not be more clear: downsampling may well make a photo appear less noisy by eliminating high frequency noise along with the detail, but it is a horrible way to reduce noise in a photo.

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