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PNG suddenly does not save in good quality?

Mar 25, 2012, 20:49
Post: #1
PNG suddenly does not save in good quality?
Yes I am new with GIMP, I've been using it for a few weeks now. I always save my images in PNG format, sometimes GIF. I messed with the checkmarks when saving my image as PNG (the ones with gamma, interlacing, etc) one day and now when I save an image, the quality is poor, and the black brushes with surround the image are very pixelly and don't blend well into black backgrounds.

any help on how I can fix this? I tried reinstally gimp but nothing worked.
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Mar 25, 2012, 21:16 (This post was last modified: Mar 25, 2012 21:17 by ofnuts.)
Post: #2
RE: PNG suddenly does not save in good quality?
(Mar 25, 2012 20:49)littlegreendog Wrote:  Yes I am new with GIMP, I've been using it for a few weeks now. I always save my images in PNG format, sometimes GIF. I messed with the checkmarks when saving my image as PNG (the ones with gamma, interlacing, etc) one day and now when I save an image, the quality is poor, and the black brushes with surround the image are very pixelly and don't blend well into black backgrounds.

any help on how I can fix this? I tried reinstally gimp but nothing worked.
Reinstalling Gimp rarely fixes anything, because Gimp's settings are kept across re-installations.

But your problem is likely not the PNG save options. I'd be more inclined to suspect that your image is in indexed color instead of full RGB (check "Image/Mode"), or got "binary" transparency if you saved as GIF.

Create a test image with some plain black text (font size: 40-50) on white background and save it as XCF and then as PNG. If it looks pixellated as PNG, then post both PNG and XCF here.

On the whole avoid GIF like the plague unless you do animations.

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Mar 25, 2012, 22:13
Post: #3
RE: PNG suddenly does not save in good quality?
The text looks fine, for some reason the brushes are the ones acting up. They were working perfectly before and now when saved, they end up being bad quality. For example, I made this image for someone's site, it was supposed to be over a black bg. As you can see, some parts of the image are colored black to blend into the bg.

http://i41.tinypic.com/r89onc.png

If you look at the image over a black bg you can see that it does not blend it. Now, here is an image with the same concept, however this was when I was having no problem.

http://image.wetpaint.com/image/1/tc0r43.../GW799H413

The mode is also set to full RGB.


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Mar 25, 2012, 23:22
Post: #4
RE: PNG suddenly does not save in good quality?
(Mar 25, 2012 22:13)littlegreendog Wrote:  The text looks fine, for some reason the brushes are the ones acting up. They were working perfectly before and now when saved, they end up being bad quality. For example, I made this image for someone's site, it was supposed to be over a black bg. As you can see, some parts of the image are colored black to blend into the bg.

http://i41.tinypic.com/r89onc.png

If you look at the image over a black bg you can see that it does not blend it. Now, here is an image with the same concept, however this was when I was having no problem.
Loaded in Gimp, enlarged the canvas, added a black layer, and spent 10 minutes squinting at the borders at 800% zoom and didn't notice anything wrong, except in a couple of places where you have left out very dark parts of the original image. I don't see anything coming from "brushes" (I would expect brush strokes).

Also insterted in this HTML:
Code:
<html>
<body>
<div style="margin:100px; padding:50px; background-color:#000000;">
<img src="bad-r89onc.png">
</div>
</body>
</html>

and couldn't find anything wrong.

Can you give the the X,Y coordinates of some pixels that aren't correct, with the RGB values you see and the ones you would have expected?

PNG is a lossless format, Gimp will normally save you image exactly as it has got it. If you suspect it transforms the image when saving it, try this:

- Load in Gimp
- Save to disk as PNG
- File/Open as layers the saved file
- Put that layer in "difference" mode
- Use the histogram dialog to hunt for pixels that aren't 0.

I sincerely doubt you'll find a problem there. I think the cause of the problem you see is external to Gimp (color profile used...)

PS: Your "good" pic is a JPEG so it doesn't really help...

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Mar 26, 2012, 00:33
Post: #5
RE: PNG suddenly does not save in good quality?
Alright here we go. Here's a better example.

http://image.wetpaint.com/image/3/jCEdIS.../GW813H440

If you look near the bottom where the black starts, you can see some large pixels. For some reason all my images have been doing that after they are saved.

This is a PNG image.
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Mar 26, 2012, 01:25
Post: #6
RE: PNG suddenly does not save in good quality?
OK, there is indeed something strange with this picture... the wolf has a very visible 8x8 pattern (look at its eye at 400% zoom)(also very visible on its throat):

[attachment=1046]

It looks as if it came from a rather low-quality JPEG. And it I get back to the previous one, it also has this pattern, although somewhat less visible (slightly better JPEG quality?)

But this since pattern doesn't appear in the text that has been added later, it comes from your source image, and is not produced when Gimp saves the image.

Can you show me the source images (or give an URL)?

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Mar 26, 2012, 03:41
Post: #7
RE: PNG suddenly does not save in good quality?
http://fc03.deviantart.net/fs50/f/2009/3..._W0LLE.jpg

That is the original image.

Like I said this just happened recently, so all these poor savings and huge pixels never showed up before.
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Mar 26, 2012, 07:24
Post: #8
RE: PNG suddenly does not save in good quality?
Must be a mistake somewhere in your workflow. The added background has no pattern. The wolf is downscaled. This should help you figure out where things went wrong, likely when you edited the wolf. If you kept intermediate versions it would be useful to check them out.

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