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Render Resize

May 2, 2012, 17:53 (This post was last modified: May 2, 2012 19:22 by Arc.)
Post: #1
Render Resize
Hi - first off I want to say I have googled and even youtubed to try and find a answer, and have failed.

I've recently started trying to learn how to use GIMP through making signatures, and for the past 2 weeks or so, it has been going fine.

Today, when attempting to resize the large image down to signature size, even though the preview shows a good quality render, after it scales the image loses all quality. Whats more, thinking it might just be a poor image, I tried to resize previously succesful images and got the same bad result.

Here are some screenshots showing pre / post scale

http://img225.imageshack.us/img225/616/render1g.jpg

Preview there is fine, and shows a good quality render (exactly what I'm looking for)

http://img684.imageshack.us/img684/9660/render2e.jpg

This is the result

I understand that the aspect box is unticked, but even with that selected the image became distorted

I have also tried cubic / Sinc, both resulting in blurry picture.
The most frustrating thing is that the preview shows that the picture can be made that small and retain it's quality, and up until now this has not been an issue.
Anyhelp would be greatly appreciated, whether I have just stupidly changed some settings I do not know.

Thanks,
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May 2, 2012, 19:58
Post: #2
RE: Render Resize
You get a floating selection, so you aren't really resizing the layer, but only a part of it.

What isn't clear to me is the original size. By how much are you scaling down? Can you post the original render (or a URL to it?)

Also why is the alpha-lock set? This could be an explanation by itself...

Keep it simple:

- "Edit/Copy" then "Edit/Paste as new layer" (or load directly from file; "File/Open as layers")
- Scale the layer making sure you keep the aspect ratio.

In some cases, when you scale down by values multiple of integer (or close to) i.e., 1/2 , 1/3, 1/4.., you can get "aliasing" effects. The cure is counter-intuitive but has a mathematical justification: before scaling down, apply a Gaussian blur the same factor: if you scale to 1/3, apply a blur of 3px.

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May 2, 2012, 20:30
Post: #3
RE: Render Resize
I tried without alpha lock, same result.

To make a working example - last week I created a basic signature using this render

http://img163.imageshack.us/img163/9383/...terbya.png

Through using basic re-scale tool, I made

http://imageshack.us/f/140/fostersign1.png/

Not brilliant, but the quality of the render was retained.

Then today, seemingly out of nowhere, the best quality render I can get is

http://img822.imageshack.us/img822/4403/fostertest.png

Looking at the two side by side, the difference in quality is clear. I just cannot understand what I did, or what setting that is on which caused this.

In the first instance, that quality was kept without the need for blurring etc.

Thanks for the reply
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May 2, 2012, 23:01
Post: #4
RE: Render Resize
Indeed. I get sharp results scaling down to 90%. But as I said above your process seems a bit contrived. And usually Sinc/Lanczos is the best interpolation.

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May 3, 2012, 06:25
Post: #5
RE: Render Resize
(May 2, 2012 23:01)ofnuts Wrote:  Indeed. I get sharp results scaling down to 90%. But as I said above your process seems a bit contrived. And usually Sinc/Lanczos is the best interpolation.


As I say, all I do is use the Scale tool on the left hand side under the tool menu, which up until now worked Angry

I've tried every other variation of scaling image, layers etc and I just can't get the thing to stay sharp
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May 3, 2012, 06:57
Post: #6
RE: Render Resize
(May 3, 2012 06:25)Arc Wrote:  As I say, all I do is use the Scale tool on the left hand side under the tool menu, w
Among other things... but why do you get a floating selection, and why is the alpha-lock set?

Can you post the XCF?

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