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NEWS: HD Photo to become JPEG XR
Barry Pearson schrieb:
I have published my own tests at the page below. My conclusion from these (admittedly limited) tests was: "For any given set of quality values, the HD Photo and JPEG 2000 files were about the same size, and significantly smaller than the JPEG file". ("Half the size" would be a fair generalisation, and at that level probably fewer nasty artefacts). The basis for these conclusions is at the following page - I won't repeat them he http://www.barrypearson.co.uk/articl...ysis_lossy.htm How do you define "quality"? What is a "quality value"? You have to be *very* careful defining terms, or you're likely comparing apples to oranges. Sorry to be picky, but one has to be pretty careful when testing. Some typical mistakes (not saying that you did it, just things to watch out for): The "quality" value of HDPhoto has nothing to do with the "quality" value of JPEG. JPEG2000 doesn't even define something like that, but lets you choose the target file size. Vendors might prefer to offer a "quality" setting, but that's then entirely vendor defined. Others measure "quality" in terms of PSNR (peak signal to noise ratio), then often logarithmic in dB. This "quality" relates pretty badly to "visual impression", it is easy to generate two images with the same dB as "quality", one of them looking great, the other looking unacceptable. Better metrics exist, none of them is perfect, but most of them are notably better than PSNR. This said, our tests do the following: i) Pick a test image set, for all images in the set: ii) compress the image to quality level x of HDPhoto iii) measure the file size returned by HDPhoto iv) compress the same image to the same file size with JPEG2000 (yes, JPEG2000 can do that) v) Use either an objective visual quality metric (we've used M-SSIM, VDP and PQS) or run subjective tests (with people actually looking at the images), and by that define a quality. vi) compile results by plotting "perceived" or "objectively measured" quality over output rate. When doing this test (and not measuring PSNR and not adjusting obscure quality settings), you really compare apples to apples. Unfortunately, and that's what I said, HDPhoto doesn't at all perform very well. And, as said, I hope that this is fixable, but the current version is not. Furthermore, please also note that the *current* test image set is still limited, more tests are to be done. The major drawback is its lack of standardization. The problem seems that camera vendors prefer to bind their customers instead of making images interchangeable. I don't see why JPEG-XR would change their position, but that's all my guesswork. Otherwise, it would have been easy just to approach the JPEG to standardize *some* type of raw format - it is IMHO just not desirable for the vendors. There IS an ISO standard raw file format. ISO 12234-2 (TIFF/EP). (It became an ISO standard in 2001, and some manufacturers such as Canon and Nikon based their own raw file formats on it). The problem is that it was never really fit for the purpose of standardised interchange, and it has become out-of-date. (In effect, DNG, also based on that standard, is ISO 12234-2 brought up-to-date and made fit for purpose). ISO are revising ISO 12234-2, and Adobe have given them permission to use the features of DNG in the revision. (Just as they gave ISO permission to use TIFF in the original version of ISO 12234-2). Given that ISO's TC42 WG18 has responsibility for TIFF/EP, it would be diversionary for another working group to "compete" to standardise a raw file format. Far better, surely, for all standards bodies and working groups to concentrate on one standard, especially if it can based on a format (DNG) that is supported in some way by nearly 200 products of various kinds. (I would like to see the revised ISO 12234-2 either BE DNG, or be compatible with DNG sufficiently for products to work with a common subset). Thanks for the pointers to TC42 (I'm SC29, so there you go), I'll ask there. In my impression, TC42 doesn't really have too much support or acceptance from the camera vendors, but I'm (currently) only watching this from the outside, so I cannot really say for sure. I'd be personally happy if any type of "raw format" standardization would arrive at a format that is really accepted and that makes image data interchangeable, but probably there are too many sensor types, or too many trade secrets - I don't know. So long, Thomas |
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NEWS: HD Photo to become JPEG XR
On Nov 30, 7:48 am, Thomas Richter wrote:
Barry Pearson schrieb: I have published my own tests at the page below. My conclusion from these (admittedly limited) tests was: "For any given set of quality values, the HD Photo and JPEG 2000 files were about the same size, and significantly smaller than the JPEG file". ("Half the size" would be a fair generalisation, and at that level probably fewer nasty artefacts). The basis for these conclusions is at the following page - I won't repeat them he http://www.barrypearson.co.uk/articl...ysis_lossy.htm How do you define "quality"? What is a "quality value"? You have to be *very* careful defining terms, or you're likely comparing apples to oranges. Sorry to be picky, but one has to be pretty careful when testing. The term "quality values", as I used it, is defined on the above page. As I said, I won't repeat it here. Specifically, at: http://www.barrypearson.co.uk/articl...sy.htm#results [snip] Given that ISO's TC42 WG18 has responsibility for TIFF/EP, it would be diversionary for another working group to "compete" to standardise a raw file format. Far better, surely, for all standards bodies and working groups to concentrate on one standard, especially if it can based on a format (DNG) that is supported in some way by nearly 200 products of various kinds. (I would like to see the revised ISO 12234-2 either BE DNG, or be compatible with DNG sufficiently for products to work with a common subset). Thanks for the pointers to TC42 (I'm SC29, so there you go), I'll ask there. In my impression, TC42 doesn't really have too much support or acceptance from the camera vendors, but I'm (currently) only watching this from the outside, so I cannot really say for sure. I'd be personally happy if any type of "raw format" standardization would arrive at a format that is really accepted and that makes image data interchangeable, but probably there are too many sensor types, or too many trade secrets - I don't know. Some camera vendors (eg. Canon, Nikon) based their raw file formats on ISO 12234-2 from TC42. Indeed, NEF files identify the TIFF/EP version used. There are actually not many sensor types - they are mostly of few general types (eg. Bayer, Fujifilm SuperCCD) but with many parametric differences that can be caterd for. That is how DNG works, as shown at: http://www.barrypearson.co.uk/articl...n.htm#examples One "trade secret" problem is with Foveon/Sigma X3F files, where documenting their details would identify internal details of the Foveon software used by some raw converters. So DNG only supports X3F images after using some Foveon software to process it, and doesn't hold its raw state. Camera manufacturers COULD use a common standard if they chose, (with a possible exception for Foveon), which is why a number of niche and minority manufacturers support DNG. (My Pentax K10D gives an option whether to use PEF or DNG, and gives the same results either way). http://www.barrypearson.co.uk/articl...#manufacturers -- Barry Pearson http://www.barrypearson.co.uk/photography/ |
#13
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NEWS: HD Photo to become JPEG XR
Barry Pearson wrote:
On Nov 30, 7:48 am, Thomas Richter wrote: Barry Pearson schrieb: I have published my own tests at the page below. My conclusion from these (admittedly limited) tests was: "For any given set of quality values, the HD Photo and JPEG 2000 files were about the same size, and significantly smaller than the JPEG file". ("Half the size" would be a fair generalisation, and at that level probably fewer nasty artefacts). The basis for these conclusions is at the following page - I won't repeat them he http://www.barrypearson.co.uk/articl...ysis_lossy.htm How do you define "quality"? What is a "quality value"? You have to be *very* careful defining terms, or you're likely comparing apples to oranges. Sorry to be picky, but one has to be pretty careful when testing. The term "quality values", as I used it, is defined on the above page. As I said, I won't repeat it here. Specifically, at: http://www.barrypearson.co.uk/articl...sy.htm#results Well, your quality settings seem to be very low - unrealistically low. You do not use those rates in real images (or, I actually wouldn't want to (- The algorithms might and will behave differently for higher quality. JPEG2000 doesn't have a "quality" at all, it's a vendor defined thing. May I ask which vendor you picked? Without that, a "quality" makes no sense at all. How do you define "examine the differences"? This is not well-defined, what do I do with these histograms to get a "quality"? Do you want to limit the maximum error? (Mathematically, this is the l^infinity metric). Not really a very usable metric - a single wrong pixel can ruin it, even though if that is in a suitable image part, you wouldn't even see it. I've here images where the absolute error for JPEG is pretty huge, but the image is pretty fine. It really depends *where* this error is in the picture. If you look at the "mean" error, (guessing that this is the *mean square error*) then that's basically PSNR (which I already mentioned). It is a fairly bad metric, but a popular one with known deficiencies. May I suggest a different way of handling it? Measuring the *file size* is much easier. Try to adjust compression parameters such that for all three methods, you get approximately the same size. Then inspect images visually or by objective metrics. I can send you code for that. Defining the quality from the histogram is unfortunately not very reasonable as well - you neglect a lot, if not all visual effects known. Especially at bitrates *that* low, a lot of nasty things happen. Examples: Human observers are more sensitive to specific spatial image frequencies than others (that's also the reason why the JPEG-1 default quantization matrix looks so weird), are less sensitive to color than to luminance, and are less sensitive to errors when those errors are in "noisy" image regions, i.e. errors can be easily hidden behind image structures. This is also the reason why every sensible image metric requires careful "subjective" testing, i.e. ask a lot of people on their opinion of the quality, then check how sensible the metric can predict those numbers. Some camera vendors (eg. Canon, Nikon) based their raw file formats on ISO 12234-2 from TC42. Indeed, NEF files identify the TIFF/EP version used. There are actually not many sensor types - they are mostly of few general types (eg. Bayer, Fujifilm SuperCCD) but with many parametric differences that can be caterd for. That is how DNG works, as shown at: http://www.barrypearson.co.uk/articl...n.htm#examples Thanks for that, I haven't really looked into DNG, though I was aware of its existence (but only that and barely more). One "trade secret" problem is with Foveon/Sigma X3F files, where documenting their details would identify internal details of the Foveon software used by some raw converters. So DNG only supports X3F images after using some Foveon software to process it, and doesn't hold its raw state. Camera manufacturers COULD use a common standard if they chose, (with a possible exception for Foveon), which is why a number of niche and minority manufacturers support DNG. (My Pentax K10D gives an option whether to use PEF or DNG, and gives the same results either way). http://www.barrypearson.co.uk/articl...#manufacturers Thus, asking frankly, why don't they? (-: So long, Thomas |
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