[Gimp-user] JPG file size increases with saving
People, I am trying to work out why there is such a large file increase when I edit a file and save it. The background info: Original file (from digital camera) - format, size, depth, geom: JPEG 680590 8 2048x1536 After opening and saving original file with defaults (85% quality): JPEG 646554 8 2048x1536 After opening and saving original file with defaults but with 100% quality: JPEG 1618121 8 2048x1536 After opening, cropping and saving original file as a PNG file with defaults (compression 9): PNG 4722953 8 2048x1536 After opening, cropping and saving original file with defaults but with 100% quality: JPEG 1631911 8 1590x1332 Questions: - When saving as JPG with 85% quality am I losing information? - How can saving as JPG with 100% quality increase information (file size)? - Why is PNG so inefficient? - imageinfo doesn't seem to be able to indicate information structure /compression information differences between the files - is there some way of doing this? Thanks, Phil. -- Philip Rhoades GPO Box 3411 Sydney NSW 2001 Australia E-mail: p...@pricom.com.au ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
Hi Philip, On 15 Jan 10 10:56 Philip Rhoades said: > - When saving as JPG with 85% quality am I losing information? Yes! > - How can saving as JPG with 100% quality increase information (file > size)? It doesn't throw so much info away. It's not actually bigger than the the raw data (i.e. total pixels x colour depth) Try saving the image as a BMP to get an indication of that. > - Why is PNG so inefficient? It's a lossless format (i.e. unlke JPG it doesn't throw any information away). It's not so much "inefficient", rather it just saves ALL the data. > - imageinfo doesn't seem to be able to indicate information > structure /compression information differences between the files - > is there some way of doing this? Not in any simple way. You're assumed to know the general benefits of the various file types for different purposes. There is some information in GIMP help. Best you read up some fuller descriptions of the various image file formats. I'm sure someone be be along in a moment with some appropriate links. Greg ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
Hi Philip, Philip Rhoades wrote: > - When saving as JPG with 85% quality am I losing information? JPG utilizes lossy compression, which means you'll loose information every time you save as JPG, even at 100% quality setting. That value does not specify the percentage of information stored in the JPG. It is just a number which allows to choose a trade-off between subjective image quality and file size. In consequence, the workflow recommendation is to routinely save as XCF and only create a JPG when the (finished) work leaves your system. > - How can saving as JPG with 100% quality increase information (file size)? As said above, it is wrong to assume you were saving 100% of the 85% of the original image's information here. In practice, one has to look at the compression artifacts to be able to adjust for minimum file size at acceptable quality. There's no way to just rely on the numbers. What happens in detail: when opening the JPG it gets decompressed to 2048x1536 RGB pixels of 3 bytes each, a whopping total of 9437184 bytes of RAM. (This holds true for any color JPG of 2048x1536 size, regardless of file size). Now when saving this image as JPG, it's these 9437184 byte of image that get compressed, regardless from where this data originated. Compressing an image of 9437184 bytes at 100% gives a larger file size than compressing the same image at 85%. There's no memory of previously used compression rates. And regardless of file size, each new JPG compression step adds new artifacts to the image, degrading quality. > - Why is PNG so inefficient? PNG offers lossless compression and isn't designed for use with photos. It excels at graphic data which e.g. has uniform color areas. regards, peter ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
People, On 2010-01-15 23:33, yahvuu wrote: > Hi Philip, > > > Philip Rhoades wrote: >> - When saving as JPG with 85% quality am I losing information? > > JPG utilizes lossy compression, which means you'll loose information > every time you save as JPG, even at 100% quality setting. > > That value does not specify the percentage of information stored > in the JPG. It is just a number which allows to choose a trade-off > between subjective image quality and file size. > > In consequence, the workflow recommendation is to routinely save as XCF > and only create a JPG when the (finished) work leaves your system. > > >> - How can saving as JPG with 100% quality increase information (file size)? > > As said above, it is wrong to assume you were saving > 100% of the 85% of the original image's information here. > > In practice, one has to look at the compression artifacts to > be able to adjust for minimum file size at acceptable quality. > There's no way to just rely on the numbers. > > > What happens in detail: > > when opening the JPG it gets decompressed to 2048x1536 RGB pixels of 3 bytes > each, a whopping total of 9437184 bytes of RAM. (This holds true for any > color JPG of 2048x1536 size, regardless of file size). > > Now when saving this image as JPG, it's these 9437184 byte of image that > get compressed, regardless from where this data originated. > > Compressing an image of 9437184 bytes at 100% gives a larger file > size than compressing the same image at 85%. There's no memory of > previously used compression rates. > > And regardless of file size, each new JPG compression step adds new artifacts > to the image, degrading quality. Firstly, thanks for the replies! What still doesn't make sense is that if the original file is JPG and one simply opens it and then saves it as another JPG file with 100% quality - you are saying that introduced artifacts are adding about 150% to the file size? (681 KB to 1.618 MB) How could the compression algorithms be so different as to cause this sort of result? - At worst I would have expected maybe a 10% increase in size . . Thanks, Phil. -- Philip Rhoades GPO Box 3411 Sydney NSW 2001 Australia E-mail: p...@pricom.com.au ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
Philip Rhoades wrote: > What still doesn't make sense is that if the original file is JPG and > one simply opens it and then saves it as another JPG file with 100% > quality - you are saying that introduced artifacts are adding about 150% > to the file size? (681 KB to 1.618 MB) How could the compression > algorithms be so different as to cause this sort of result? - At worst > I would have expected maybe a 10% increase in size . . well firstly, 1.6MB are not that bad in comparison to 9MB of raw RGB data, right? (just try saving to uncompressed BMP as Greg suggested). Btw, 100% quality for JPG gives very little visible advantage over the default 90% setting. The relationship between quality value, file size and perceived image quality is very delicate. Any assertion has to be made with a lot of weasel words. So yes, compression artifacts have a tendency to hinder compression, resulting in larger file sizes after re-compression to comparable quality. A similar effect is caused by noise. So to get optimal JPG files, it's best to use a RAW->XCF->JPG workflow where the JPG is created only once. Just have a look at the advanced settings in the JPG save dialog to get a first impression of what machinery is at work here. There also was a very long thread on gimp.developer on that very quality setting... How does image quality compare if you adjust the quality slider such that the resulting file size is about 680KB? regards, peter ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
On Fri, 15 Jan 2010 21:56:40 +1100, Philip Rhoades wrote: > - Why is PNG so inefficient? PNG is not efficient for real life images (ordinary photos). PNG is very efficient for computer generated images (like a snaphot of a program window, or a relatively simple paint, or vector graphics, or some CAD drawing export), where large areas use exactly the same pixel value from one pixel to the other. Cristi -- Cristian Secară http://www.secarica.ro/ ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
Hi Philip, On 15 Jan 10 12:53 Philip Rhoades said: > What still doesn't make sense is that if the original file is JPG > and one simply opens it and then saves it as another JPG file with > 100% quality - you are saying that introduced artifacts are adding > about 150% to the file size? (681 KB to 1.618 MB) The %age, isn't one of straight file size reduction, but relates to the areas of the image to be averaged. The the more you reduce the quality the more you increase the potential for larger areas to be averaged. A "busy" image will not suffer much averaging regardless of the compression requested, but one with large areas of broadly similar colour, sky, painted walls, car bodywork, etc will have progressively larger areas averaged the more you reduce quality and the file size will reduce accordingly. Some images, for example, where there is a load of tumbling water and spray will barely reduce in size t all even at higher compression levels as no part of the image has a large enough plain area to allow it to be averaged. > How could the compression algorithms be so different as to cause > this sort of result? - At worst I would have expected maybe a 10% > increase in size . . I think you are assuming the whole imaged is compressed equally, regardless of the level of detail and colour change from one pixel to the next. Only in images with large areas of similar colour will the fle size reduce much at higher compression levels. The control is more one of "reduce this if you can", rather than "reduce it whatever the consequenses". Greg Chapman http://www.gregtutor.plus.com Helping new users of KompoZer and The GIMP ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
On Fri, Jan 15, 2010 at 4:56 AM, Philip Rhoades wrote: > People, > > I am trying to work out why there is such a large file increase when I > edit a file and save it. The background info: Google the difference between "lossy" and "lossless" image compression. Once you understand the fundamental differences your question will be answered (actually, it will be a non-question) :) ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
People, On 2010-01-16 00:11, yahvuu wrote: > Philip Rhoades wrote: >> What still doesn't make sense is that if the original file is JPG and >> one simply opens it and then saves it as another JPG file with 100% >> quality - you are saying that introduced artifacts are adding about 150% >> to the file size? (681 KB to 1.618 MB) How could the compression >> algorithms be so different as to cause this sort of result? - At worst >> I would have expected maybe a 10% increase in size . . > > well firstly, 1.6MB are not that bad in comparison to 9MB of raw RGB data, > right? > (just try saving to uncompressed BMP as Greg suggested). > > Btw, 100% quality for JPG gives very little visible advantage over the > default 90% setting. > > The relationship between quality value, file size and perceived image quality > is very delicate. Any assertion has to be made with a lot of weasel words. > So yes, compression artifacts have a tendency to hinder compression, > resulting in larger file sizes after re-compression to comparable quality. > A similar effect is caused by noise. So to get optimal JPG files, it's > best to use a RAW->XCF->JPG workflow where the JPG is created only once. > > Just have a look at the advanced settings in the JPG save dialog to get > a first impression of what machinery is at work here. There also was a > very long thread on gimp.developer on that very quality setting... > > How does image quality compare if you adjust the quality slider > such that the resulting file size is about 680KB? To my eye, it doesn't look much different - I guess I see the pixellation more quickly when the image is enlarged . . I guess what is confusing is this: - there was a loss of information when the first JPG was saved in the digital camera memory from the CCD - when the JPG is uncompressed by GIMP into RAM, there is no loss of information (?) - when GIMP then saves the same image as a new JPG at 100% quality (I would have thought that this meant not losing any more information), that the second JPG would be compressed/created in much the same way as the first and therefore would be about the same size . . Good to know that this happens anyhow . . of course I have no control over the file format that the camera uses and cropping a camera image and actually getting a result that is 2.5 times the size of the original is a bit annoying . . Thanks, Phil -- Philip Rhoades GPO Box 3411 Sydney NSW 2001 Australia E-mail: p...@pricom.com.au ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
Philip Rhoades writes: > What still doesn't make sense is that if the original file is JPG and > one simply opens it and then saves it as another JPG file with 100% Because JPEG isn't meant to be saved at 100% quality. The JPEG FAQ, http://www.faqs.org/faqs/jpeg-faq/part1/section-5.html, says: Except for experimental purposes, never go above about Q 95; using Q 100 will produce a file two or three times as large as Q 95, but of hardly any better quality. Q 100 is a mathematical limit rather than a useful setting. If you see a file made with Q 100, it's a pretty sure sign that the maker didn't know what he/she was doing. Do a web search on jpeg quality "100%" and you'll find lots of detailed discussions of this. GIMP's "Show preview in image window" check box is extremely helpful, and lets you see the trade-off in quality versus size. It's too bad it's not enabled by default. ...Akkana ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
Hi Philip, On 15 Jan 10 18:27 Philip Rhoades said: > - when the JPG is uncompressed by GIMP into RAM, there is no loss of > information (?) No further loss, but the restored image is subject to those averages created when the image was originally compressed. > - when GIMP then saves the same image as a new JPG at 100% quality > (I would have thought that this meant not losing any more > information), You shouldn't take 100% too literally. Think of it more as "best quality", but the best that the JPG algorithm achieves is not "no change". > that the second JPG would be compressed/created in much the same way > as the first and therefore would be about the same size . . Remember that it is working on data that is already corrupted so it further corrupts it, again averaging the larger areas of similar colour. If you didn't want it to compress it a bit (even at 100% quality) you wouldn't be using selecting a JPG format when saving it would you? You'd choose a lossless format instead. > of course I have no control over the file format that the camera > uses Most cameras do have a range of compression options available within their menu system. It won't have the variability of the GIMP but probably will have a "Normal" setting plus a high and low option. > and cropping a camera image and actually getting a result that is > 2.5 times the size of the original is a bit annoying . . But now you realise how much the data is compressed at even "normal" levels, you realise how good the algorithm was that the JPEG came up with! :-) Greg Chapman http://www.gregtutor.plus.com Helping new users of KompoZer and The GIMP ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
On Fri, Jan 15, 2010 at 12:27 PM, Philip Rhoades wrote: > - there was a loss of information when the first JPG was saved in the > digital camera memory from the CCD Correct > - when the JPG is uncompressed by GIMP into RAM, there is no loss of > information (?) Since JPG is not lossless, there is always a loss of information. Or more specifically the same JPG can be interpreted differently by different software, so opening it in GIMP might look different than another program perhaps. Once an image is saved as JPG there's no way to get the original image back from that JPG file. > - when GIMP then saves the same image as a new JPG at 100% quality (I > would have thought that this meant not losing any more information), > that the second JPG would be compressed/created in much the same way as > the first and therefore would be about the same size . . 100% quality does not mean no loss of info, just means that it's as close to the original as JPG is capable of getting. It's still not going to be identical to the original. > Good to know that this happens anyhow . . of course I have no control > over the file format that the camera uses and cropping a camera image > and actually getting a result that is 2.5 times the size of the original > is a bit annoying . . That's why the expensive/professeional cameras output in raw format, so the photographer can have total control. :) FWIW, if you have a Canon you very well might be able to install CHDK and get raw images, that's what I've done with my SD550 and SD1000. Depending on your purpose for the final JPG file, there are other ways to make the file smaller. Saving as progressive vs baseline usually makes a small difference in size. You can use the program jpegoptim to optimize (losslessly) and reduce filesize, and you can strip out EXIF/thumbnail/etc header info to make the file smaller without affecting the actual image data either (assuming you're not using the EXIF for rotation/etc in whatever program you're displaying the image in). For best quality/size trade-off when you save your JPG in GIMP I would use the "show preview in window" (something like that) option which will show the resulting compressed JPEG in a window. Then you can adjust the quality and other settings and see how it looks. I usually adjust it as low as I can until the image appears to degrade, then I bump it up a notch and choose that. For me, around 75% seems to be a pretty good combination of small file size and good quality. There are also JPEG tools that allow you to losslessly crop/rotate etc your pictures. Check out jpegtran from jpegclub.org or one of these programs which supposedly include the same functionality: http://jpegclub.org/losslessapps.html ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
Hi, On Sat, 2010-01-16 at 05:27 +1100, Philip Rhoades wrote: > I guess what is confusing is this: > > - there was a loss of information when the first JPG was saved in the > digital camera memory from the CCD > > - when the JPG is uncompressed by GIMP into RAM, there is no loss of > information (?) > > - when GIMP then saves the same image as a new JPG at 100% quality (I > would have thought that this meant not losing any more information), > that the second JPG would be compressed/created in much the same way as > the first and therefore would be about the same size . . Actually, you get almost no further degradation if you save the image again with the same settings that were used for the first save. The JPEG plug-in even stores information in the image when the image is opened and it will use that information to save it in the best possible way when you save it again. Just leave all controls at their default values. Note that I said "almost". Of course the image will suffer a little. But you won't get significantly better results if you increase the JPEG quality or change other settings in the save dialog. You just get a larger file. Sven ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
Actually, you get almost no further degradation if you save the image > again with the same settings that were used for the first save. The JPEG > plug-in even stores information in the image when the image is opened > and it will use that information to save it in the best possible way > when you save it again. Just leave all controls at their default values. > > Note that I said "almost". Of course the image will suffer a little. But > you won't get significantly better results if you increase the JPEG > quality or change other settings in the save dialog. You just get a > larger file. > > > Sven Quality is relative to what you need, how the image is used as well. If it's for internet use, 70% or so is reasonable quality. Image weight adds up fast if you have a lot of large images. I don't do print media so someone else would need to talk to it, but I commonly here that 300-600 dpi is requested whereas for the internet resolution is much less of a factor. If all I've been given is a .jpg I'll typically save it as a .png along the way. ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
On Fri, 15 Jan 2010 21:56:40 +1100, Philip Rhoades wrote: > - When saving as JPG with 85% quality am I losing information? Yes, but still with the same 85% quality you may obtain different results by changing other parameters. Just look at the following example. Note the file size for each, but most of all, look at the color quality and the outline of objects (the files are quite small; save them somewhere and look at them by switching forth and back so you can notice the differences). The JPEG were both saved with 85%, but one with subsample for best quality and the other with subsample for minimum file size: http://www.secarica.ro/misc/monopoly.bmp http://www.secarica.ro/misc/monopoly.png http://www.secarica.ro/misc/monopoly_gimp_hi_quality.jpg http://www.secarica.ro/misc/monopoly_gimp_minim_size.jpg Take the .bmp and do further tests with the save options. Cristi -- Cristian Secară http://www.secarica.ro/ ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
On 15.01.2010 19:59, Greg Chapman wrote: >> - when GIMP then saves the same image as a new JPG at 100% quality >> (I would have thought that this meant not losing any more >> information), > > You shouldn't take 100% too literally. Especially if the value is not a percentage. Regards, Michael -- GIMP > http://www.gimp.org | IRC: irc://irc.gimp.org/gimp Wiki > http://wiki.gimp.org | .de: http://gimpforum.de Plug-ins > http://registry.gimp.org | ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] Color Management Woes
Frank Gore píše v Čt 14. 01. 2010 v 21:35 -0500: > Sorry, those were links to the version of the pictures as displayed by > Picasa, which has the metadata stripped. The direct download links are > as follows: > I thought your camera would be very unusual to provide JPEGs w/o metadata... > Adobe RGB: > http://lh6.ggpht.com/_HAZjMzZWrtc/S05qkb7KkYI/BCw/oPJ80XXYH-Y/d/_GOR3359.JPG > $ exiftool -a -G -H _GOR3359.JPG | grep Color [File] - Color Components: 3 [EXIF] 0xa001 Color Space : Uncalibrated [MakerNotes]0x0037 Color Space : Adobe RGB $ exiv2 -pa _GOR3359.JPG | grep Color Exif.Pentax.ColorSpace Short 1 Adobe RGB Exif.Pentax.ColorTemperature Short 1 0 Exif.Pentax.ColorInfoUndefined 18 32 131 31 100 31 125 32 156 33 72 32 246 31 51 31 10 0 0 Exif.Photo.ColorSpaceShort 1 Uncalibrated > As I stated in my original post, the sRGB image has the EXIF tag > "Color space" set as "sRGB". The Adobe RGB picture has that same EXIF > tag set as "Uncalibrated". That's how it comes right out of the > camera. Changing it to "Adobe RGB" does not change anything. Gimp > still doesn't detect the color space properly and still assumes it's > sRGB. Here you talk about Exif.ColourSpace. The info above is included in the blob of nonstandard metadata of Pentax... They do in on purpose, since the standard for Exif does not allow AdobeRGB: "While the EXIF header in your images does have a field called "color space", use of this data is very limited because the only two values allowed in the EXIF color space field are (1) sRGB and (2) unspecified." Anyway, it would be good if graphics programs try to identify also the known maker notes to find out the colour space. Regards, Milan Knizek knizek (dot) confy (at) volny (dot) cz http://www.milan-knizek.net - About linux and photography (Czech language only) ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] Color Management Woes
Frank Gore píše v St 13. 01. 2010 v 18:20 -0500: > > In any case, like I mentioned in my original post, I specifically have > it set to "Ask what to do" in the Preferences, and it doesn't ask. > I agree with you, it is definitely a bug. GIMP should not assume that JPEG is in sRGB colour space when exif header says "Uncalibrated". regards, Milan Knizek knizek (dot) confy (at) volny (dot) cz http://www.milan-knizek.net - About linux and photography (Czech language only) ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
On Fri, 2010-01-15 at 13:32 -0600, Paul Hartman wrote: > On Fri, Jan 15, 2010 at 12:27 PM, Philip Rhoades wrote: > > - when the JPG is uncompressed by GIMP into RAM, there is no loss of > > information (?) > > Since JPG is not lossless, there is always a loss of information. Or > more specifically the same JPG can be interpreted differently by > different software, so opening it in GIMP might look different than > another program perhaps. I'm fairly sure this is not true - there is only one way to uncompress a JPG file, so all programs should create the same uncompressed version. -- David ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
On Sat, 16 Jan 2010 10:54:23 +1100, David Hodson wrote: > I'm fairly sure this is not true - there is only one way to uncompress a > JPG file, so all programs should create the same uncompressed version. Not true - I know that at least different versions of ImageMagick will decompress the same JPEG slightly differently, probably due to different rounding. -- < Jernej Simončič ><><><><>< http://eternallybored.org/ > ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
On Fri, Jan 15, 2010 at 5:54 PM, David Hodson wrote: > On Fri, 2010-01-15 at 13:32 -0600, Paul Hartman wrote: >> On Fri, Jan 15, 2010 at 12:27 PM, Philip Rhoades wrote: > >> > - when the JPG is uncompressed by GIMP into RAM, there is no loss of >> > information (?) >> >> Since JPG is not lossless, there is always a loss of information. Or >> more specifically the same JPG can be interpreted differently by >> different software, so opening it in GIMP might look different than >> another program perhaps. > > I'm fairly sure this is not true - there is only one way to uncompress a > JPG file, so all programs should create the same uncompressed version. >From an old JPEG FAQ: "Another important aspect of JPEG is that decoders can trade off decoding speed against image quality, by using fast but inaccurate approximations to the required calculations. Some viewers obtain remarkable speedups in this way. (Encoders can also trade accuracy for speed, but there's usually less reason to make such a sacrifice when writing a file.)" Also, of course, things like color management and other kinds of post-processing can cause differences when the same file is opened in different programs. ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
Philip Rhoades wrote: > I am trying to work out why there is such a large file increase when I > edit a file and save it. The background info: > > Original file (from digital camera) - format, size, depth, geom: > > JPEG 680590 8 2048x1536 [..] > After opening, cropping and saving original file as a PNG file with > defaults (compression 9): > > PNG 4722953 8 2048x1536 There's something funny there. If the image has been cropped, how can it be the same dimensions as the original (2048x1536) (unless you have then done a "resize" you didn't mention)? -- Bob Long ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
On Fri, 2010-01-15 at 18:07 -0600, Paul Hartman wrote: > On Fri, Jan 15, 2010 at 5:54 PM, David Hodson wrote: > > On Fri, 2010-01-15 at 13:32 -0600, Paul Hartman wrote: > >> [...] the same JPG can be interpreted differently by > >> different software, so opening it in GIMP might look different than > >> another program perhaps. > > > > I'm fairly sure this is not true - there is only one way to uncompress a > > JPG file, so all programs should create the same uncompressed version. > > >From an old JPEG FAQ: > > "Another important aspect of JPEG is that decoders can trade off > decoding speed against image quality, by using fast but inaccurate > approximations to the required calculations. Good point. I would argue that's not really interpreting the JPG differently, just being more or less accurate in your interpretation. However, the user may still see some minor differences. > Also, of course, things like color management and other kinds of > post-processing can cause differences when the same file is opened in > different programs. Of course. -- David ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
Re: [Gimp-user] JPG file size increases with saving
Bob, On 2010-01-16 11:32, Bob Long wrote: > Philip Rhoades wrote: > >> I am trying to work out why there is such a large file increase when I >> edit a file and save it. The background info: >> >> Original file (from digital camera) - format, size, depth, geom: >> >> JPEG 680590 8 2048x1536 > > [..] > >> After opening, cropping and saving original file as a PNG file with >> defaults (compression 9): >> >> PNG 4722953 8 2048x1536 > > There's something funny there. If the image has been cropped, how can it > be the same dimensions as the original (2048x1536) (unless you have then > done a "resize" you didn't mention)? Sorry, copy and paste error on the description - the PNG was not cropped . . Regards, Phil. -- Philip Rhoades GPO Box 3411 Sydney NSW 2001 Australia E-mail: p...@pricom.com.au ___ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user