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The HiFiC model we show is already the low model :) We show JPEG and BPG at the same rate to visualize how low the bitrate of our model actually is. And for JPE

The HiFiC model we show is already the low model :) We show JPEG and BPG at the same rate to visualize how low the bitrate of our model actually is. And for JPEG and BPG we show 1x, 2x, and so on to visualize how many more bits the previous methods need to look similar visually.

nullc 6y ago
Sure, but it isn't low rate enough to produce the level of gross artefacts needed to train the viewer to recognize faults in the images. E.g. after looking at those jpeg images you're able to flip to much higher rate jpegs and notice blocking artefacts that a completely unprepared subject would fail to notice. In my work on lossy codecs I found that having trained listeners was critical to detecting artifacts that would pass on quick inspection but would become annoying after prolonged exposure. From a marketing fairness point since the only codec you evaluate 'below knee' is jpeg, it risks exaggerating the difference. It would be just about as accurate to say that jpeg can't achieve those low rates-- since no one will use jpeg at a point where its falling apart. This work is impressive enough that it doesn't need any (accidental) exaggeration. I think it's best to either have all comparison points above the point where the codecs fall apart, or have a below-knee example for all so that it's clear how they fail and where they fail... rather than asking users to compare the gigantic difference between a failed and non-failing output.
- ebg13 6y ago
  > asking users to compare the gigantic difference between a failed and non-failing output It isn't. It's asking users to compare what happens at a particular bitrate as a demonstration that it works (well!) at bitrates significantly lower than what anything else can safely achieve. To get comparable quality you need several _times_ the number of bytes with another codec. While I agree that it would be _interesting_ to see what happens below HiFiC's knee, the location of the knee for individual codecs is irrelevant to the comparison that really matters, because users just want high quality without high size or low size without low quality. And this clearly produces the best quality at the least size by a mile. I think they did a fantastic job of showing both how each code looks at the same size and also how many bytes it takes for other codecs to reach the same quality. Showing what it looks like when HiFiC degrades if you go to an even lower than already extremely low bitrate would be fun and neat for comparing HiFiC's bitrates but has little bearing on how it compares to other codecs.
- atorodius 6y ago
  In addition to my sibling comment, I would like to add: > since no one will use jpeg at a point where its falling apart. Hence we also put it at bitrates people actually use :) And then the point should be that HiFiC uses much fewer bits. > below-knee for HiFiC We actually did not train lower than this model, HiFiC^lo. That it works so well was somewhat surprising to us also! From other GAN literature, it seems reasonable to expect the "below-knee" point for this kind of approach to still look realistic, but not faithful anymore. I.e., without the original, it may be hard to tell that it's fake.
  - nullc 6y ago
    > expect the "below-knee" point for this kind of approach to still look realistic, but not faithful anymore. If so, that might be kinda cool on its own. (and perhaps also useful for anti-forensic purposes, e.g. use it as a de-noising mechanism that makes it more difficult to identify the source camera)

nullc 6y ago

Sure, but it isn't low rate enough to produce the level of gross artefacts needed to train the viewer to recognize faults in the images. E.g. after looking at those jpeg images you're able to flip to much higher rate jpegs and notice blocking artefacts that a completely unprepared subject would fail to notice. In my work on lossy codecs I found that having trained listeners was critical to detecting artifacts that would pass on quick inspection but would become annoying after prolonged exposure. From a marketing fairness point since the only codec you evaluate 'below knee' is jpeg, it risks exaggerating the difference. It would be just about as accurate to say that jpeg can't achieve those low rates-- since no one will use jpeg at a point where its falling apart. This work is impressive enough that it doesn't need any (accidental) exaggeration. I think it's best to either have all comparison points above the point where the codecs fall apart, or have a below-knee example for all so that it's clear how they fail and where they fail... rather than asking users to compare the gigantic difference between a failed and non-failing output.

ebg13 6y ago
> asking users to compare the gigantic difference between a failed and non-failing output It isn't. It's asking users to compare what happens at a particular bitrate as a demonstration that it works (well!) at bitrates significantly lower than what anything else can safely achieve. To get comparable quality you need several _times_ the number of bytes with another codec. While I agree that it would be _interesting_ to see what happens below HiFiC's knee, the location of the knee for individual codecs is irrelevant to the comparison that really matters, because users just want high quality without high size or low size without low quality. And this clearly produces the best quality at the least size by a mile. I think they did a fantastic job of showing both how each code looks at the same size and also how many bytes it takes for other codecs to reach the same quality. Showing what it looks like when HiFiC degrades if you go to an even lower than already extremely low bitrate would be fun and neat for comparing HiFiC's bitrates but has little bearing on how it compares to other codecs.
atorodius 6y ago
In addition to my sibling comment, I would like to add: > since no one will use jpeg at a point where its falling apart. Hence we also put it at bitrates people actually use :) And then the point should be that HiFiC uses much fewer bits. > below-knee for HiFiC We actually did not train lower than this model, HiFiC^lo. That it works so well was somewhat surprising to us also! From other GAN literature, it seems reasonable to expect the "below-knee" point for this kind of approach to still look realistic, but not faithful anymore. I.e., without the original, it may be hard to tell that it's fake.
- nullc 6y ago
  > expect the "below-knee" point for this kind of approach to still look realistic, but not faithful anymore. If so, that might be kinda cool on its own. (and perhaps also useful for anti-forensic purposes, e.g. use it as a de-noising mechanism that makes it more difficult to identify the source camera)