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Old Nov 29, 2016, 8:55 PM   #21
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Your image posted here is only 70KB, which is not going to show as much detail. You may have used too low a quality setting for it to look sharp. I like to use Irfanview to do resizing, as it has some very good algorithms, and also has a plug - in to allow setting a specific file size , which is something I do for posting here.
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Old Nov 29, 2016, 10:41 PM   #22
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Hi TCav,
I'm sorry. I don't get it. Are you saying that, the the downsized picture being fuzzier than the full sized one, makes sense? If so, would you say that it's fuzzier because there are less pixels spread over the same area?
Hi VTphotog,
I downsized it to 1024x768, as are the others. So, all downsizing algorithms are not equal?
...... john

Last edited by Shinnen; Nov 29, 2016 at 10:46 PM. Reason: Add more
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Old Nov 30, 2016, 4:18 AM   #23
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Quote:
Originally Posted by Shinnen View Post
I downsized it to 1024x768, as are the others. So, all downsizing algorithms are not equal?
That's true, but that's not what I'm saying.

What I'm saying is that noise is individual errant pixels, and the process of downsampling (ANY process of downsampling) reduces the impact a single pixel has on image quality.

When you reduce a 12 megapixel image (4000x3000) to 3/4 of a megapixel (1024x768), the errant pixels will be averaged with their surrounding accurate pixels, such that their effect on overall image quality is negligible at worst, and is probably non-existant.
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Old Nov 30, 2016, 9:34 PM   #24
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Hi TCav,
I still don't get it. Aren't you trying to explain why a downsized image is fuzzier than the original? Well, it sounds like you're saying just the opposite "the errant pixels will be averaged with their surrounding accurate pixels, such that their effect on overall image quality is negligible at worst, and is probably non-existant".
..... john
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Old Dec 1, 2016, 5:24 AM   #25
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When you downsample (downsize) an image, you do lose detail. That is, individual pixels that contain accurate image data will be averaged with surrounding pixels to produce a less accurate but smaller portion of the total image. But along with that, you also lose the effect of inaccurate, or errant pixels, so image noise is lost as well.

So downsampling reduces the effect of all pixels, whether they contain accurate image data or image noise.

What I'm saying is that you shouldn't mess with your original image files in an attempt to reduce image noise, as the techniques used will often lessen detail as well, and common use of your images will almost always result in an image with less noise anyway.
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Old Dec 1, 2016, 8:52 AM   #26
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Hi TCav,
Alright. I think the problem here is that I don't understand the mechanics of downsizing, wrt pixel changes. Thanks for your explanation. I do appreciate it.
... john
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Old Dec 1, 2016, 10:45 AM   #27
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If you start with a 4000x3000 image, and you want to reduce the resolution down to 1333x1000 image, each pixel in the reduced image is the result of averaging a 3x3 pixel area of the original image.

4,000 X 3,000 = 12,000,000
1,333 X 1,000 = 1,333,000
12,000,000 / 1,333,000 = 9

This is an overly simplified explanation of downsampling, but it shows that detail as well as noise are diluted in the reduced image.
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Old Dec 1, 2016, 11:45 AM   #28
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Hi TCav,
Now you're talking my language ... simplicity.
"What I'm saying is that you shouldn't mess with your original image files in an attempt to reduce image noise ..." So, you're basically saying that any processing of a jpg/raw/etc. may produce a more pleasing image, but the new file will have lost some information from the original?
....... john
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Old Dec 1, 2016, 3:46 PM   #29
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Processing the RAW file is OK, as long as you do a "Save As..." so that you still have the RAW file to go back to. That goes for anything that changes the resolution as well as the file format, i.e.: RAW, PSD, DNG,TIF, PNG, JPG, etc.

I'm also saying that the vast majority of the time, there's no reason to reduce noise. Many unrelated steps in post processing will reduce noise anyway. And if you've already reduced the noise, don't do it again.
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Old Dec 1, 2016, 6:00 PM   #30
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"Many unrelated steps in post processing will reduce noise anyway." Now ....... that's interesting. Would you mind elaborating on that statement.
..... john
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