I spent ages retouching a photo, but when I export it there are a bunch of artifacts in a large area where I used cage transform (but not in other areas where I performed equivalent transformations). Specifically, there's a line at the right-hand border of the cage -- across it the transformations aren't contiguous, and black is showing as two very different values. I'm attaching a crop of the problem area below. Does anyone know what's causing this and ideally how to fix it?? I'm doing this as a favor for someone who anticipates it appearing in print.
It's also worth mentioning that the exported image has grain-type artifacts in areas not affected by the other problem. They're not present in GIMP, just the exported image. In all fairness, the original image isn't the crispest, but this is still a lot more quality-loss than I'd anticipate.
FYI, I'm running 2.10, and the workspace is sRGB 8-bit gamma integer. (Could the problem be that GIMP has been surreptitiously displaying in 32-floating this whole time, even though it says it's in 8-integer?)
AFAIK Gimp 2.10 always work in 32bit-FP internally which is all for the better, in 8-bit round-off errors creep in very quickly: do a bump map in 2.8 and compare with 2.10 and you'll see there is no real debate. Making the image 32-bit FP makes processing faster (no conversions) at the cost of 4x the RAM.
Export artifacts may be be due to the export format and/or the format parameters (compression, etc...).
(12-15-2019, 11:46 PM)Ofnuts Wrote: Not very clear what the perceived problem is.
AFAIK Gimp 2.10 always work in 32bit-FP internally which is all for the better, in 8-bit round-off errors creep in very quickly: do a bump map in 2.8 and compare with 2.10 and you'll see there is no real debate. Making the image 32-bit FP makes processing faster (no conversions) at the cost of 4x the RAM.
Export artifacts may be be due to the export format and/or the format parameters (compression, etc...).
So perhaps the issue is that the 32-floating is making it appear like the image has enough data to make my transformations, but when it tries to apply them to the 8-bit source they can't be reproduced?
I doubt the artifacts are from the export settings I selected. I get this result when exporting to PNG at level 9 (both with and without gamma embedded), and when exporting to uncompressed TIF. If there's a more lossless option than those I should be trying, let me know.
Do you not see the problem on the image, or do you mean you don't know what could be causing it? The problem is the export artifacts, I just don't know how to address them because I don't know what's causing them.
(12-16-2019, 06:01 AM)wildisthewind Wrote: Do you not see the problem on the image, or do you mean you don't know what could be causing it? The problem is the export artifacts
I can see that the sample image is not a uniform dark gray. There are variations in colour. But don't think they are export artifacts, but rather part of the image before export.
(12-16-2019, 06:01 AM)wildisthewind Wrote: Do you not see the problem on the image, or do you mean you don't know what could be causing it? The problem is the export artifacts
I can see that the sample image is not a uniform dark gray. There are variations in colour. But don't think they are export artifacts, but rather part of the image before export.
I'll see about taking a screenshot in-program and post the comparison.
It's not just the color variation, the transformed areas also aren't where they're supposed to be. You that can see in the image I attached that the folds of fabric are not contiguous across that line.
Quote:..the transformed areas also aren't where they're supposed to be. You that can see in the image I attached that the folds of fabric are not contiguous across that line.
Is that just not the way the tool works? Very obvious when using few control points: example https://i.imgur.com/RK6PmMw.jpg
You might get a better result using the Warp tool, maybe constrained with a feathered selection but needs care: https://i.imgur.com/PJVgUvi.jpg
Gimp has a hidden tool, n-point deformation, just as well it is hidden, horribly broken, but if you are willing to install and try Krita that has a working grid transform tool. https://i.imgur.com/xwDpY7e.jpg
(12-16-2019, 06:28 AM)Blighty Wrote: I can see that the sample image is not a uniform dark gray. There are variations in colour. But don't think they are export artifacts, but rather part of the image before export.
Attaching a screenshot of the image in GIMP prior to export.
(12-16-2019, 11:35 AM)rich2005 Wrote:
Quote:..the transformed areas also aren't where they're supposed to be. You that can see in the image I attached that the folds of fabric are not contiguous across that line.
Is that just not the way the tool works? Very obvious when using few control points: example https://i.imgur.com/RK6PmMw.jpg
You might get a better result using the Warp tool, maybe constrained with a feathered selection but needs care: https://i.imgur.com/PJVgUvi.jpg
The cage transform tool actually worked excellently for my purposes. Given all the folds of fabric, the warp tool wasn't going to have a believable result. I took a screenshot of the original image as well as the final result in GIMP so you can see why I used the tool I did, and how it worked for me.
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Hopefully this will clear up the confusion about my initial question. As you can see, the screenshot from the GIMP session does not show the artifacts that end up in the exported image.
I took your image "Screenshot of transformed & retouched image" and added as a new layer your image "Crop of exported PNG". I then used the Ofnuts tool Realign Layers to accurately align the two layers. The "Crop of exported PNG" layer looks better than the "Screenshot of transformed & retouched image" layer. But comparing a screenshot with a png crop is like comparing apples and oranges.
xcfgz file attached (with paths still visible). Use Gimp's File > Open to open the xcfgz file.
(12-16-2019, 08:56 PM)Blighty Wrote: I still don't see the problem.
I took your image "Screenshot of transformed & retouched image" and added as a new layer your image "Crop of exported PNG". I then used the Ofnuts tool Realign Layers to accurately align the two layers. The "Crop of exported PNG" layer looks better than the "Screenshot of transformed & retouched image" layer. But comparing a screenshot with a png crop is like comparing apples and oranges.
xcfgz file attached (with paths still visible). Use Gimp's File > Open to open the xcfgz file.
Thanks, Blighty. I'll take a look at the file when I'm back at my computer.
Basically, I'm just trying to understand why the exported image doesn't look like the end-result of the transformations within GIMP. The exported result was the same when exported as an uncompressed TIF, so I can't imagine it's an actual compression artifact, but rather that there's some discrepancy between what GIMP is showing me and the image data it's working from. The fact that I can get the workable result within GIMP makes me think that there might be some way to preserve what GIMP shows in an exported image, but without knowing what's causing that discrepancy I can't figure out how.
Well, I found something useful: I'm able to get GIMP to match the exported image by unchecking "proof colors" in View>Color Management. So whatever "proof colors" is doing was obscuring things when I made the transformations. I'll go look up that menu item and see what I can learn about it, but if there's any way to have that "proofing" applied during the export, maybe I can get away with having worked under those display settings.
