[HN Gopher] Jpeg2png: Silky smooth JPEG decoding - no more artif...
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Jpeg2png: Silky smooth JPEG decoding - no more artifacts (2016)
Author : todsacerdoti
Score : 127 points
Date : 2020-07-10 10:19 UTC (12 hours ago)
(HTM) web link (github.com)
(TXT) w3m dump (github.com)
| wtallis wrote:
| This strikes me as conceptually similar to the problem of
| printing floating point numbers. A naive algorithm will convert
| the binary floating point to decimal and print that out, with
| potentially many trailing digits that are more or less garbage.
| The more human-friendly algorithms figure out the
| shortest/simplest decimal that would be rounded to the same
| binary floating point quantity, and prints that instead.
| jandrese wrote:
| Yes, I've long wanted a floating point print function that
| understands that 3.999999999999 should be printed as "4".
| colejohnson66 wrote:
| My $.02: I'd prefer it say 3.9999999... than 4 so students
| learn of the inaccuracy of floating point. If one wants a
| rounded output, one should round before printing.
| jandrese wrote:
| Students can be taught using the standard library printf()
| or whatever.
|
| It's not as easy as "just round" though, because you don't
| know where the digits start to repeat. A smart function
| would also print 4.1249999999999 as 4.125.
|
| A fancy unicode version could even include the mathematical
| notation to print 3.333333333333 as 3.3 with a line over
| the trailing 3. Or 4.2525252525 as 4.25 with the bar over
| the 25. Might be asking too much of a simple print function
| though, this might end up being an extension of the halting
| problem.
| moonchild wrote:
| Sounds like you want a computer algebra system, not a
| floating point format algorithm.
| jandrese wrote:
| I don't think I'm the only one. I was thinking as I wrote
| the response that such a system might have to include a
| whole lot more math than it looks at the surface, which
| is probably why it doesn't exist as a general solution.
|
| But maybe there could be some heuristics that get it
| right 99% of the time (with a don't use this library for
| serious number crunching disclaimer).
| wtallis wrote:
| I've used various HP scientific and graphing calculators
| that have functions to convert a floating point number to
| a symbolic representation of a rational number, or a
| fraction of pi. These functions are approximate, and
| their tolerance for how large the denominator of the
| fraction may get is determined by the current setting for
| how many decimal digits the display of numbers is rounded
| to. In practice, this works pretty well, and they
| implemented this capability long before they had a full
| CAS on any of their calculators.
| wtallis wrote:
| 3.999... vs 4 is a bad example, because 4 is exactly
| representable, and if your calculation gives you a result
| of 3.999... [garbage digits omitted] then it means there
| was roundoff error along the way and your computed result
| is something that is strictly not equal to 4.
|
| A better example would be something like 1/5, which for
| almost every purpose is better printed as 0.2 instead of
| 0.20000000298023223876953125. The latter is absurdly long
| and gives the misleading impression of precision far in
| excess of the ~7 decimal digits that single-precision
| floats are capable of representing.
|
| The difference between 0.2 and that long string is due to a
| slightly different cause than a difference between 3.999...
| and 4: the latter is likely due to information loss during
| calculations and may be reduced and sometimes avoided
| entirely with careful ordering of calculations and using
| the right rounding modes. But 0.2 can never be exactly
| represented, even as the input to a chain of calculations.
| The loss of accuracy is an unavoidable first step of trying
| to put 0.2 into a binary FPU register.
|
| Students _should_ learn about the pitfalls of floating
| point arithmetic. But preferably in a way that doesn 't
| leave them with the impression that it is a non-
| deterministic process that always leaves you with trailing
| garbage that needs to be ignored.
| 0x0 wrote:
| But 3.9999999..... === 4. It is literally the same number.
| wtallis wrote:
| Your floating-point calculator won't give you infinite
| trailing nines, but it may very well give you something
| like 3.99999976158 (approximately the largest float below
| exactly 4) or 3.99999999999999955591 (approximately the
| largest double below 4).
| Kednicma wrote:
| You and the rest of this thread's participants may be
| interested to know that the problem was solved a while ago; you
| want the "Dragon4" algorithm from "How to Print Floating-Point
| Numbers Accurately" [0]. Indeed, the problem is difficult, and
| having implemented the algorithm, I can confirm that it has
| earned its reputation. Numeric algorithms are hard and the only
| reward is accuracy.
|
| [0] https://lists.nongnu.org/archive/html/gcl-
| devel/2012-10/pdfk... or use your search engine
| karmakaze wrote:
| For the first image I much prefer the jpeg decoded image to the
| de-noised one. The de-noised one just looks like it was sent
| through a low-pass/median filter and loses contrast, detail, and
| texture. If you flip between the full-sized images the jpeg2png
| looks like vaseline on the lens.
|
| The naming is also odd. I don't imagine it would do well with
| text (which are the sorts of images I associate with png) that
| was jpeg encoded then decoded with it.
| KarlKemp wrote:
| It says it is _specifically targeted_ at images that should
| have been png in the first place.
| Scaevolus wrote:
| Knusperli is similar: https://github.com/google/knusperli
|
| Instead of trying to smooth the entire image, it reduces blocking
| artifacts by finding plausible coefficients that reduce
| discontinuities at block boundaries (jpegs are encoded as a
| series of 8x8 blocks). "jpeg2png gives best results for pictures
| that should never be saved as JPEG", but knusperli works well on
| normal photographic content, since it only tries to remove
| blocking artifacts.
|
| > A JPEG encoder quantizes DCT coefficients by rounding
| coefficients to the nearest multiple of the elements of the
| quantization matrix. For every coefficient, there is an interval
| of values that would round to the same multiple. A traditional
| decoder uses the center of this interval to reconstruct the
| image. Knusperli instead chooses the value in the interval that
| reduces discontinuities at block boundaries. The coefficients
| that Knusperli uses, would have rounded to the same values that
| are stored in the JPEG image.
| enriquto wrote:
| > Instead of trying to smooth the entire image, it reduces
| blocking artifacts by finding plausible coefficients that
| reduce discontinuities at block boundaries
|
| This is essentially the same thing, but using slightly
| different regularizers. In both cases, an image is found that
| whose jpeg compression is identical to the given one, by
| selecting the "most regular" image among the large family of
| such images. Jpeg2png minimizes the total variation over the
| whole image, and knusperly only along the boundaries of the
| blocks. The effect is quite similar at the end.
| Scaevolus wrote:
| The effects are quite different, since reducing total
| variation also reduces texture, which is important to
| perceived quality. Here's a direct comparison-- note how
| knusperli retains slightly more detail instead of
| oversmoothing:
| https://mod.ifies.com/f/200710_lena_decode_comparison.png
| crazygringo wrote:
| This is really cool, but in other comments I'm reading that good
| JPEG encoders and decoders _depend on knowing the other_.
|
| That you can design a better JPEG encoder for a known reference
| decoder (which decoded version best matches the original), and
| you can likewise design a better JPEG decoder for a known
| reference encoder.
|
| But now that there are _both_ encoders _and_ decoders trying to
| be more efficient and non-blocky respectively... it feels like a
| mess. Even more so because a decoder never knows which encoder
| was used, and an encoder never knows which decoder.
|
| Is there any solution to this mess? Is there a best practice
| here? Since most JPEG's are probably viewed on the web, do all
| browsers share the same decoder, and so effort is best spent on
| the encoder? Or even while encoder improvements are made
| specifically for the algorithms browsers use, can improvements to
| decoders still be made that remain improvements, instead of e.g.
| "overfitting" and actually making things worse?
|
| This just feels like a bit of an "improvements race" on both
| sides which leaves me a little dizzy in trying to understand
| it...
| webmaven wrote:
| _" jpeg2png gives best results for pictures that should never be
| saved as JPEG. Examples are charts, logo's, and cartoon-style
| digital drawings."_
|
| Interesting value proposition.
|
| There may be equivalents for other misused file types/formats.
| The obvious one is the inverse case of photos saved as GIFs, but
| I imagine audio and text (eg. PDF malapropisms?) are possible
| too.
| jandrese wrote:
| I just tried it with a text heavy screenshot, a common scenario
| where the JPEG encoding produces a poor result with lots of
| speckle around each letter.
|
| The result is very good. The speckling is effectively
| eliminated without smearing the letters.
|
| JPEG Encoded, 25% quality:
| http://jubei.ceyah.org/overcompressed/crop-jpg.png
|
| JPEG2PNG: http://jubei.ceyah.org/overcompressed/crop-
| converted.png
| fireattack wrote:
| Why the whole picture shifted? This can't be good
| indigo945 wrote:
| I find the text on the reference decoded image easier to
| read, despite the colorful speckles surrounding the words.
| JPEG2PNG doesn't smear the letters a lot, but does appear to
| slightly deform them. Consider the leading "a" in "add
| license, readme", whose upper half seems to be closer
| together after the JPEG2PNG run.
|
| However, now I'm wondering whether my impression that the
| reference decoded text is easier to read is a form of
| overfitting. I have spent the past 20 years reading low-
| quality JPEG screenshots on the internet, maybe the
| perceptual centers of my brain have developed an unblocking
| algorithm?
| dmitriid wrote:
| And then someone uploads this image to twitter/facebook, and it
| gets triply re-encoded and resized with the worst algorithms
| known to man :(
| BlackLotus89 wrote:
| https://mobile.twitter.com/NolanOBrien/status/12045574989900.
| .. twitter now doesn't cripple uploaded images, but tries to
| preserve all information except exiv data.
| [deleted]
| dmitriid wrote:
| Kudos to Twitter!
|
| Now if only they stopped cropping images to rand()xrand()
| in timelines pretending they employ advanced ML algorithms
| to do so :)
| fireattack wrote:
| It's not random though. They likely show most contrasted
| area (with maybe some face detection).
| makapuf wrote:
| I d say the issue is the prpgram here, a compressor program
| might have heuristic to detect png-favored images vs photos. I
| cannot imagine we couldn't detect the easy cases reliably
| (because I'd say often images are more in a category or
| another). Crop the image to 64x64, try png and if the result is
| sufficiently small continue, else convert to jpg ?
| 0-_-0 wrote:
| Now we just need an adversarially trained neural network to fill
| in detail [1] and we have a 21st century JPEG decoder!
|
| [1] Implemented for a custom compressor: https://hific.github.io/
| lazyjones wrote:
| And one day, a law enforcement officer will use it on a bad
| quality JPEG image and one of the innocent persons whose photos
| were used to train the NN will be arrested.
| leeoniya wrote:
| here's one that upscales extremely well:
|
| https://github.com/TianZerL/Anime4KCPP
| [deleted]
| ris wrote:
| Interesting project, but its name sells it incredibly short.
| locofocos wrote:
| "For pictures that have been reencoded to JPEG multiple times I
| recommend shred."
| (https://www.gnu.org/software/coreutils/manual/html_node/shre...)
|
| That's the funniest thing I've read in a while.
| etaioinshrdlu wrote:
| The interesting thing is that advanced _encoders_ might create
| JPEGs that produce odd results with this decoder.
| a_e_k wrote:
| Yes, this is definitely an interesting question. Earlier this
| year I implemented a version of trellis quantization for some
| compression experiments that I've been tinkering with in my
| spare time. My code considers more possibilities than just
| rounding to the nearest quantization step when it deems that
| the bit rate savings in after entropy encoding may be worth the
| additional image loss (e.g., it might even completely zero a
| coefficient). That would violate this decoder's assumption that
| the original DCT coefficient must have been within a limited
| range around the quantization step.
|
| I know that mozjpeg [1] features trellis quantization for JPEG
| encoding. I wonder how this decoder would do with that?
|
| [1] https://github.com/mozilla/mozjpeg
| ajb wrote:
| This is a poor-mans version of the deblocking filter which you
| find in recent video standards, but jpeg was to early to get it.
|
| The advantage of those over this is that the encoder knows that
| the decoder is going to run the filter, and it can use that in
| its perceptual model to choose an encoding which looks most like
| the original _after deblocking_. Video codecs also use the
| deblocked version as reference frames. So you see these artifacts
| in mpeg-2 video and jpeg, but not more recent ones.
| pents90 wrote:
| It's long past time to retire Lena as the canonical test image in
| CG.
| pkulak wrote:
| Lena and Big Buck Bunny for life!
| enriquto wrote:
| Why? It's like "lorem ipsum" at this point.
| KarlKemp wrote:
| Fish have no concept of water in very much the same way as
| you not seeing the problem here.
| flumpcakes wrote:
| How about you respect women in tech more and stop assuming
| they're so fragile that they need men to change an industry
| so they don't get their feelings hurt.
|
| Women are people, they don't care.
| NoSorryCannot wrote:
| If lorem ipsum were softcore erotica...
| enriquto wrote:
| What if I told you it actually is?
|
| > Quis autem vel eum iure reprehenderit, qui inea voluptate
| velit esse, quam nihil molestiae consequatur, vel illum,
| qui dolorem eum fugiat, quo voluptas nulla pariatur?
|
| Translation: Who has any right to find fault with a man who
| chooses to enjoy a pleasure that has no annoying
| consequences, or one who avoids a pain that produces no
| resultant pleasure?
|
| This text could very well be the first page of a softcore
| erotica (or even hardcore!). The rest of the text is not
| usually visible. But then again, neither is the rest of
| lena!
| YetAnotherNick wrote:
| I knew other commenters would bash you for proving their
| point, but this is quite the best comeback I have seen in
| long time.
| NoSorryCannot wrote:
| This is a really big stretch in interpretation but also
| in plausibility, since Latin is a dead language.
|
| But if it were true, then you'd have it your way: it'd
| also be inappropriate in professional settings that don't
| naturally necessitate it.
| 2038AD wrote:
| > This is a really big stretch in interpretation
|
| According to Wikipedia[0], "[t]he placeholder text is
| taken from parts of the first book's discourse on
| hedonism." The first book being the first book of
| Cicero's _De finibus bonorum et malorum_.
|
| [0] https://en.wikipedia.org/wiki/De_finibus_bonorum_et_m
| alorum
| NoSorryCannot wrote:
| Least plausible of all is that someone would try to shore
| up this argument in good faith.
| 2038AD wrote:
| To be honest I'm sure it isn't erotica just as the Holy
| Bible is not despite verses like Ezekiel 23:20. I must
| also confess I did find the revelation a little amusing.
| It certainly says something about men (whether that's
| just the men of 70s from when both originate).
| crazygringo wrote:
| Then... you'd be wrong.
|
| It's a philosophical argument against Epicurianism. Which
| has as much in common with softcare erotica as the phone
| book.
|
| Not sure what your point is.
| crazygringo wrote:
| Seriously. People wonder why there aren't enough women in CS.
|
| Things like the canonical test image being a sexy "come hither"
| look, coming from a Playboy centerfold, definitely don't help.
|
| And it's not enough to say "well the rest of the centerfold
| isn't shown". Come on. We all know the source of the image.
|
| And "tradition" is far less important than CS being a welcoming
| environment for all people.
|
| Computer science is a profession. Let's use images that are
| appropriate for a professional setting.
| FriendlyNormie wrote:
| Shut up you dumb fucking faggot.
| hombre_fatal wrote:
| The idea that women can't handle something like the Lena
| lorem ipsum seems more potentially offputting to women, to
| me.
|
| Seems ironic that guys race over each other to claim a
| picture of a woman is the shibboleth that keeps women out.
| NoSorryCannot wrote:
| Fortunate for us that there is a similar race to apologize
| for erotic photographs in tech demos, as if it's not an
| obvious anachronism.
|
| Really, defending something so clearly out-of-place is
| deeply suspicious. Maybe everyone can handle it but why are
| we being asked to?
| flumpcakes wrote:
| If you find Lenna "erotic" and "out-of-place" then you
| probably shouldn't watch TV or 90% of media.
|
| It's a picture of a model's face. You're an adult, deal
| with it.
| NoSorryCannot wrote:
| It is astonishing that we can't even agree that the photo
| is erotic.
|
| Or that there's a meaningful difference between media you
| choose to consume for entertainment (which may be honest-
| to-goodness porn and that's _fine_) and irrelevant
| eroticism casually sprinkled in tech demos that don't
| explicitly involve sex.
|
| I wish we could at least be real about the facts in
| evidence.
| adrianmonk wrote:
| OK, time for my pet theory on this.
|
| It's not the picture itself that creates an obstacle. It's
| that emotionally-aware people want to go into a career
| where they like being around their co-workers.
|
| So if they get the impression that many of the people in
| the field are completely tone-deaf about basic stuff, they
| start asking themselves questions like, "Since I have
| limited time on this planet, why would I want to spend it
| where a good percentage of the people around me are
| insufferable asshats?" And then they pick some other field.
| Not because they can't handle it. Because they know they
| can do better for themselves.
| crazygringo wrote:
| Of course women can _handle_ it. We 're all adults.
|
| But is it _appropriate in context_? Is it _welcoming_? If
| you have a choice of jobs, is it the kind of environment
| you _prefer_?
|
| Or is it contributing to an image of "we're a bunch of
| immature boys who think it's funny to use a Playboy
| centerfold, har har, wait till you hear the sexist jokes we
| tell at lunch".
|
| It's not the end of the world. But a welcoming and
| inclusive work environment is the sum of hundreds of little
| things. This is one of those things.
|
| And come on -- the old line "what's the matter, can't you
| handle a joke?" is the oldest line in the book for
| "defending" sexist behavior. Expecting women to just
| "handle something" is not the right approach. We can be
| better than that.
| hombre_fatal wrote:
| To put a finer point on my comment, I'm claiming that
| it's not something that _needs_ to be handled. Women can
| handle it in the same way they can handle a cloudy day or
| a man not racing over to hold the door open.
|
| I would suspect your shrill infantilization of women and
| the vicarious outrage on the behalf of women is something
| much harder to handle if you want to minimize the
| handling women need to do.
|
| How many people reading this even saw or knew about the
| uncropped Lena picture until they saw men on HN/Reddit
| nodding vigorously at each other over over how many women
| pass on STEM because of it.
|
| I see outrage like yours and wonder when was the last
| time you actually polled a woman's opinion on something
| like Lena. I'd wager 95+% of women roll their eyes that a
| cropped Playboy shot even moves the needle.
| repiret wrote:
| My first programming job was for a media processing
| company, and we used the Lena image, and it's origin was
| well known, and we were mostly young men so we all found
| copies of the entire shoot, and they were occasionally
| involved in office pranks. None of us learned it from
| HN/Reddit because those weren't things in 2000.
|
| I cannot imagine it was a welcoming environment for
| women.
| tehjoker wrote:
| >> a man not racing over to hold the door open.
|
| It's telling that you think this is something that would
| even annoy most women, especially in a professional non-
| dating context. The women I know would feel creeped out
| if someone did that at work. Honestly, even in dating if
| you're "racing" to open the door it looks desperate. When
| done naturally some women like it and some think it's
| archaic.
| bityard wrote:
| I'm sorry you have to endure such an antagonistic social
| environment. Where I live (midwest US), it's considered
| polite for all people hold the door open for all others,
| regardless of gender.
|
| I'm a male and if I worked in a place where women sneered
| at me for holding the door for them, I guess I would
| start only holding the door for men.
| crazygringo wrote:
| Holding the door open for all genders is widely seen as
| polite and fine, for whoever arrives at the door first,
| man or woman. It's an optional courtesy.
|
| Having a man "race over" to hold a door, and doing so
| _because they 're a woman_ where he wouldn't for another
| man, in a professional context, is creepy and weird.
|
| Do you see the difference? What you're describing in the
| midwest is fine. But it's not what the parent was
| responding to. The "antagonistic social environment" with
| "women sneering" you're describing is a total straw-man
| of your own imagination.
| flumpcakes wrote:
| Thank you. This is very well put. It makes me quite angry
| to see people racing to remove images or language that at
| a push could be seen as offensive, to protect groups that
| don't need or want it.
|
| It's insulting to suggest your black co-worker can't use
| the same language you've always used because you're now
| saying they are more fragile.
|
| It seems to be a race to the bottom in the name of
| inclusivity and all we're doing is everything but
| actually improving the opportunities of groups that are
| "under represented" in CS.
|
| Instead of "banning Lenna" how about we create free
| resources teaching CS skills in a way that will interest
| women/"others".
|
| Does that mean making the slides pink?
|
| Solving problems to do with manging boyfriends?
|
| No. That's insulting, because women are people like
| everyone else so stop treating them as fragile brainless
| creatures that need to be wrapped in cotton wool just to
| survive in the scary man's world.
| crazygringo wrote:
| I don't think _I 'm_ the one being shrill here. ;)
|
| Unfortunately, your type of attitude is precisely the
| problem. You deny a problem exists, attack anyone who
| suggests fixing it, and resort to questioning character
| and intelligence.
|
| I'm sorry that this topic is making you angry. But
| sometimes it's important to hear other voices. In your
| case, instead of making a wager, why don't you simply
| talk to some of your female friends. You don't need to
| "poll" them, just have a friendly conversation. Don't ask
| them whether they can "handle" it, but what they would
| _prefer_.
|
| Your eyes might be opened.
|
| I'm talking from actual diverse workplace experiences
| with issues like this. You don't appear to be, or else I
| don't think you'd be saying the things you are.
| ashearer wrote:
| > Women can handle it in the same way they can handle a
| cloudy day
|
| Going with that, then why create that cloudy day when it
| would take very little effort not to?
|
| And what message does it send to actively defend creating
| those cloudy days?
| 2038AD wrote:
| I guess the flip-side is that CS is so welcoming and
| inclusive that tech conferences will invite former sex
| workers and celebrate them. No slut-shaming from the
| techies!
| lazyjones wrote:
| > is it appropriate in context?
|
| Depends on whether you would consider an image very
| similar to many, many others that get compressed to JPEG
| is "appropriate" (i.e. relevant, representative), or
| whether you are asking as a prude.
|
| > Is it welcoming?
|
| I can't see anything unwelcoming about that picture, at
| least not in any other way than many people's flattering
| profile pictures on social media. It's just a head of an
| attractive woman, shot by a professional photographer.
| rotskoff wrote:
| Came here to make the exact same comment, agree completely!
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