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Pixelation occurs when I make images smaller

Jul 11, 2011, 16:58
Post: #1
Pixelation occurs when I make images smaller
Hello, thanks for your time -

I assure you I did some Googling before I posted here, so I'll try to be quick. I am making an image smaller (from 1200 pixels wide to 700), and no matter what I try it always turns out pixelated. I hate it! I just want the size of the image to get smaller without compromising the quality of said image. Here's what I've tried:

- Saving to different formats before resizing (TIF, PNG, etc)
- Changing the X and Y resolution from 150, to 300, even 900 before resizing. It seems to have no effect.
- Changing the interpolation from cubic to the others (the others ones all look worse)

I am at a loss! I am using "image/scale image" to resize, by the way. And the original image was a 1200-wide TIF. Can anyone help? Google has been useless. I don't see why I'm not able to increase the number of pixels while making the image smaller to maintain the integrity of the original image.

Any help you could provide would be greatly appreciated!

-Benefit
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Jul 11, 2011, 17:58
Post: #2
RE: Pixelation occurs when I make images smaller
Posting here the image would help...

Shot in the dark: something that sometimes happens (and this can be what you call "pixellation") is "spatial frequency folding". Some regular pattern in your picture, scaled down, gets close to one pattern/pixel, so some of the pattern disappears, while the rest gets exaggerated. The solution is "low-pass filter" your image so that no pattern ends up with a frequency higher than a pixel. This is easy: just apply a gaussian blur (Filter/Blur/Gaussian) corresponding roughly to your scale factor (so for 1200->700, use a 2px gaussian blur) before scaling down (this "blurring" can be systematic, you'll never lose any thing with it since you scale down...).

As to the scale down algorithm, there is no good reason those days to not use sinc/lanczos. It's not the default because it requires more PCU power than cubic, but those days all computers are powerful enough.

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Jul 11, 2011, 18:03
Post: #3
RE: Pixelation occurs when I make images smaller
(Jul 11, 2011 17:58)ofnuts Wrote:  Posting here the image would help...

Here is the image post-resizing. It actually doesn't look TERRIBLE, but it's not where I would want it.

http://historicalbanyusa.org/wp-content/...maller.png

I will try your suggestion of using sinc. The blur thing seems convoluted to be honest, but I will try that too. Maybe I will do a little comparison... actually, you know what, what I will do is upload the original, then a variation of it using different settings and upload them all to imgur. I can't do that right this second, but I will.

Thanks for your help!

-brandon
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Jul 11, 2011, 18:55
Post: #4
RE: Pixelation occurs when I make images smaller
Yes, the blur thing is against "common sense" but its has a scientific justification and it works. For instance, in another forum, this picture had the problem (plain rescale on left, pre-blur on the right)(see in particular the green bench in the front, and the side of the ramp):

[attachment=525]

Your picture isn't too pixellated, except the jaw line of the lady in the middle.

Comparing and drawing your own conclusions in the way to go...

Btw, the file format has no influence on this, JPG is good enough with decent quality settings (>80). GIF is a different matter:since it reduces the number of colors this can lead to extra pixellation.

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