Moonlight

by Jakub

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1,605 reputation
414
bio website vyznev.net
location Helsinki, Finland
age
visits member for 3 years, 10 months
seen May 22 at 15:14

I'm a PhD student in biomathematics, working on stochastic individual-based models of evolution in spatially structured populations. My other interests include cryptography, programming games and puzzles, photography and graphic design.


I'm the main author and maintainer of the Stack Overflow Unofficial Patch (SOUP), a user script for browsers with GreaseMonkey-compatible user script support (Firefox, Chrome, Opera, possibly Safari) that fixes or works around a number of outstanding issues with the Stack Exchange user interface.

I tend to answer a lot more questions than I ask. Some answers I'm rather proud of:

CC-Zero Please consider any (original) code I post to Stack Overflow and other Stack Exchange sites to be released under CC-Zero unless stated otherwise. You may do whatever you want with it and don't have to credit me in any way, although of course that would be nice.


2d
awarded  Popular Question
Apr
11
comment How to take upright grave stones without squatting down?
Still, it can certainly work, and you (already) have my +1 for that. I just wanted to point out some potential issues in advance. In the end, the only real way to find out if this method will give acceptable results for the OP is for them to go out, take some test shots and try it. (One thing I would suggest for the OP is getting as far from the gravestone as they reasonably can, and using a long lens / zoom setting to take the picture. The less you need to change the perspective in post, the less likely it is to look "funny".)
Apr
11
comment How to take upright grave stones without squatting down?
That's true, and I do have some experience with this technique myself. But with architecture, you don't usually end up with visible surfaces in the picture that would've been hidden if had been actually taken face-on.
Apr
11
comment How to take upright grave stones without squatting down?
This can be a good solution, but do note that it can sometimes produce a weird-looking perspective. For example, if you applied it to a picture of a low gravestone taken from higher up, the top side of the gravestone would remain visible even after the tilt correction, possibly making it look as if it was slanted. The background will also look quite different from what you'd get by moving the camera lower.
Mar
21
comment How can I add a border to a JPEG photo without affecting quality?
I didn't vote (up or down), but you might want to work on your spelling and grammar to give a better first impression (and also, honestly, to make your answer easier to read). Also, this question already has several answers (and mine, especially, turned out quite long); at some point, some people may start downvoting (or at least not upvoting) answers that don't clearly add something new to the existing ones. Also, try to structure your answer so that the important bits stand out at a glance; in this case, the only part you've highlighted in bold is an unimportant footnote.
Mar
19
comment How can I add a border to a JPEG photo without affecting quality?
@thomasrutter: I used 4:2:0 subsampling for all my tests, since IME that's the most common setting in general use (and since, for the original border task, it's the worst-case situation). It's also what the test images I downloaded from Wikipedia used, so there's no difference there. I can't tell with 100% certainty what mattdm used, since he converted all his images to PNG, but it sure looks like 4:2:0 too.
Mar
19
comment How can I add a border to a JPEG photo without affecting quality?
@mattdm: Ps. There does seem to be a difference between resaving the JPEG directly with "Use quality settings from original image", and copy-pasting it to a new image window and saving it from there (again at q75); the latter gives a PSNR of 36.2973, slightly worse than resaving directly (but still a lot better than you got with ImageMagick). I'd assume that's because the copy-paste step makes GIMP forget any compression settings it saved as internal metadata when the JPEG was opened.
Mar
19
comment How can I add a border to a JPEG photo without affecting quality?
@mattdm: It seems to be quite software-dependent; I tried reproducing your results from that answer in GIMP, and it seems GIMP (v2.8.10, at least) is quite a bit better at preserving JPEG quality than ImageMagick (whatever version you tested). Your first image, saved once at q75, has a PSNR of 34.0298, while the one saved twice at q75 has one of just 32.8169 (and the one resaved 8 times has a PSNR of 32.6459). In comparison, saving the same source image once in GIMP at q75 gives a PSNR of 36.4560; opening and resaving it at the same quality drops it only slightly, to 36.3295.
Mar
19
comment How can I add a border to a JPEG photo without affecting quality?
Ps. I'm pretty often on chat, if you'd prefer to continue this discussion there.
Mar
19
comment How can I add a border to a JPEG photo without affecting quality?
@thomasrutter: I don't know; that's just the first test image and the first settings I tried. I linked to all the tools and source images I used so you could reproduce the results yourself; it took me less than 15 minutes to do this quick test, including Googling for "PSNR", reading the Wikipedia article and finding the ImageMagick help page, so you should be able to reproduce it in five at most. You're the one with oddball (and demonstrably counterfactual) ideas about how JPEG compression works here, so I'd say it's up to you to test them and not just expect to have data spoon-fed to you.
Mar
19
comment How can I add a border to a JPEG photo without affecting quality?
@thomasrutter: OK, fine. Download this JPEG image, open it in GIMP, and resave it twice: once with "Use quality settings from original image", and once with quality raised to 40. Compare each JPEG with the uncompressed base image. Using ImageMagick compare, I get a PSNR of 34.5826 for the original JPEG, 34.5752 for the copy resaved with same quality settings, and 34.3653 for the one resaved at q40. Good enough?
Mar
19
comment How can I add a border to a JPEG photo without affecting quality?
@thomasrutter: Furthermore, if you do not believe that post, why not just test it yourself (or look at the test images I included in my answer)? It's easy enough to check that opening a JPEG image in GIMP, and re-saving it with "Use quality settings from original image", causes only minimal (though, alas, not always zero) degradation, whereas changing the quality setting (even slightly upwards!) usually leads to significantly higher quantization losses.
Mar
19
comment How can I add a border to a JPEG photo without affecting quality?
@thomasrutter: I can't downvote a comment, so I'll just point you to the original forum post describing the feature, and in particular, this quote: "If you have only made a few changes to the image, then re-using the same quantization tables will give you almost the same quality and file size are the original image. This will minimize the losses caused by the quantization step, compared to what would happen if you used different quantization tables."
Mar
17
comment How can I add a border to a JPEG photo without affecting quality?
@tepples: You're right; I've removed that paragraph. For some reason, I was under the impression that toggling progressive mode would cause the quality settings not to match, but a quick test seems to confirm that I was wrong about that.
Mar
17
revised How can I add a border to a JPEG photo without affecting quality?
remove mistaken paragraph about progressive encoding
Mar
16
answered How can I add a border to a JPEG photo without affecting quality?
Mar
16
comment How can I add a border to a JPEG photo without affecting quality?
@WarrenYoung: To change the color of the padding blocks, you'd presumably need to change just the first (DC) coefficient, and leave the others at zero. Of course, the coefficients are compressed, so... anyway, it should be doable, but I agree that it's not as trivial as it might seem.
Feb
23
comment How to fix uneven/gradient lighting on a canvas with white background?
@Simon: One trick you can use to speed up the "heal selection" tool is to scale down the scan, then do the masking and healing, and then scale it back to original size. It's not like you need to resynthesize all the details of the paper grain, anyway, especially if you're just going to blur it away.
Feb
14
awarded  Explainer
Feb
14
revised How can I best take a tripod on a plane trip?
copyedit, add actual question statement