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Image Quality and Resizing

Mar 6, 2014, 23:45
Post: #1
Image Quality and Resizing
Just wondering some techniques or tutorials, dealing with image resizing. When photos are enlarged or downsized the images can go quite blurry depending on the new size....So looking for a way to keep great image quality when resizing heavily...
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Mar 7, 2014, 01:07
Post: #2
RE: Image Quality and Resizing
K, I can see a big difference. Thx for replying..
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Mar 7, 2014, 01:07
Post: #3
RE: Image Quality and Resizing
K, I can see a big difference. Thx for replying..
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Mar 7, 2014, 01:50
Post: #4
RE: Image Quality and Resizing
There are a few scripts & plugins that can help (2 1/2 built in) with smartly sharpening or blurring depending on if you're scaling up (sharpening) or down(blurring)

The ones that I've tested & work well are:

(*for scaling down only, preserves quality)
1. (Built in)
Selective blur
Filters > Blurs > Selective blurs
(varied results)
- first, scale down to preview & see what areas are affected
- undo the scale down
- adjust selective blur to focus on all those areas or the most affected area possible, pay attention to line edges/ overall quality.
Selective blur works best to smartly remove hsv noise while preserving edges, but could work well for pre-down scaling.


2. (add-on, simple .scm to folder)
Scale in steps
http://registry.gimp.org/node/9676

-It will appear under the "Script-fu" menu
To apply it, drag & drop it into the Gimp script folder (NOT the share one)
Edit > Preferences > Folders > Script (to find the folder path)

--------------

*For scaling up
(Built-in)
Unsharp mask (2nd version of unshapr variant is the 1/2 but gives a nice result)
1. After scaling up, "Filters > Enhance > unsharp mask..."
2. Turn up the ammount slider first until its sharper without any artifacts
Then turn up a little the radius slider.

Unsharp mask (GEGL experimental, also built in)
1. After scaling up, "Tools > GEGL Operation..."
2. Click the drop down box & navigate down to "unsharp-mask"
3. Have both sliders at the left, & slowly bring the top slider it up step by step
*I recommend doing this by clicking on the number box & pushing up on the keyboard arrow keys. First the "Dev" slider, then if needed the "scale"
NOTE: The higher the value, the longer it will take to process


============
Add-on
(A plugin sub-filter)
Resynthesizer Plug-in (for scaling small images up to about 300w x 250h)
sharpen by synthesis
Pros
- Works well for adding crips textureness to pixel art or icons after scaling up Smile
see this example: (link) http://gimpforums.com/attachment.php?aid=3119
Cons:
- is slow on any size bigger than max recommend above, *However, if you copy a section of a large layer @300wx250, thats a way you could get it done.

1. (a layer with no alpha channel) magic wand select background
2. Select > Invert (to select the object)
3. Filters > Enhance > Sharpen by synthesis

"In order to succeed, your desire for success should be greater than fear of failure." BC
[Image: 29uocaf.png]
iFS007 tut vids on YT ~ auto color B&W landscape tut
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