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Old Dec 2, 2016, 8:54 AM   #31
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As I explained, the simple act of downsampling reduces noise, but so do a lot of other steps in post processing. For instance, JPEG files are compressed using a lossy compression, which means that detail as well as noise will be diminished when you convert an uncompressed image to JPEG. You can adjust the level of compression of a JPEG file, but you can't turn it off entirely. So the process of saving an image to a JPEG file will reduce noise.

In addition, adjusting the hue, saturation, and/or brightness lessens the impact of noise on image quality. That is, errant pixels are usually much brighter than the surrounding accurate pixels (hence "errant"), and are usually at their highest level. So when you adjust the portion of an image in which an errant pixel exists (if not the entire image), to increase the level of the accurate pixels, the level of the errant pixel can't be increased as much (if at all). As a result, the difference between the accurate pixels and the errant pixel is reduced, and thus it's impact on image quality.

And, btw, the process of upsampling, which frequently occurs during printing, also reduces noise. A 4000x3000 resolution image, when printed on a 1200 dpi printer must be upsampled to 4800x3600, when printing even just a 4x6 photo.
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Old Dec 2, 2016, 10:48 AM   #32
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Thanks TCav,
I had no idea about these things.
... john
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Old Dec 2, 2016, 4:14 PM   #33
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So "Noise Reduction" should be one of the last things you do to your images, and I doubt that, after everything else you may do to your images, you would have very much noise anyway.
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Old Dec 3, 2016, 11:00 AM   #34
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I am of the contrary opinion. (I often am) Noise, if it is sufficient to bother with, should be removed or reduced as early in post-process as possible, and preferably in the Raw development stage. Certainly before conversion to Jpeg, which treats noise as detail, and creates artifacts which are more difficult to remove than the initial noise.
Noise pixels are factored in with wanted pixels by photo editing software, when doing any processing, creating some amount of inaccuracy in the process, so, if your goal is to create an accurate representation of a scene, it should have the noise minimized at the outset.
In most cases, I don't bother much with noise reduction, because the intended display method isn't going to show the noise anyway.
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Old Dec 3, 2016, 4:08 PM   #35
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Quote:
Originally Posted by VTphotog View Post
In most cases, I don't bother much with noise reduction, because the intended display method isn't going to show the noise anyway. [emphasis mine. -TCav]
On this, we agree.
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Old Dec 3, 2016, 4:22 PM   #36
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This is a 100% crop of a larger image of mine:



It's noisy.

But the noise is only noticeable in the out-of-focus blur of objects outside the depth of field (mainly, the boards and metal panels in the background). The noise that occurs in the in-focus areas is lost in the surrounding detail.

And none of the noise appears when the entire image is reduced (downsampled) for display here:

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