| | <<<Back 1 day (to 2017/08/22) | 20170823 |
| Badabing_ | Is there a way to make GhostScript use Flate on JPEG2000 rather than re-encoding them to jpeg? | 05:52.23 |
| | well I came up with a behemoth of a command to get around the lack of JPEG2000 | 06:15.35 |
| | gswin64c -o output.pdf -q -dNOPROMPT -sDEVICE=pdfwrite -dAutoRotatePages=/None -dDetectDuplicateImages=true -dCompatibilityLevel=1.7 -c ".setpdfwrite << /ColorACSImageDict << /VSamples [ 1 1 1 1 ] /HSamples [ 1 1 1 1 ] /QFactor 0.08 /Blend 1 >> /ColorImageDownsampleType /Bicubic /ColorConversionStrategy /LeaveColorUnchanged >> setdistillerparams" -f input.pdf | 06:15.40 |
| | woops, I probably don't need the compatibiltylevel still in there, that was just a test | 06:15.55 |
| | gswin64c -o output.pdf -q -dNOPROMPT -sDEVICE=pdfwrite -dAutoRotatePages=/None -dDetectDuplicateImages=true -c ".setpdfwrite <</ColorACSImageDict <</QFactor 0.4 /HSamples [1 1 1 1] /VSamples [1 1 1 1] /Blend 1>> /GrayACSImageDict<</QFactor 0.4 /HSamples [1 1 1 1] /VSamples [1 1 1 1] /Blend 1>>>> setdistillerparams" -f input.pdf | 06:37.37 |
| kens | Badabing_ you can simply set ColorImageFilter to /Flate to use that isntead of JPEG. JPEG2000 (as you probably know) is patent encumbered and requires a licecne for encoding, which is why it is not available as a compression option in the output from Ghostscript. | 07:03.46 |
| Badabing_ | kens: I did that and the PDF ended up gigantic. | 07:12.10 |
| | This will only use Flate on the images that really need it | 07:12.21 |
| kens | You command line doesn't seem to use Flate at all | 07:12.45 |
| | Maybe I missed it | 07:12.49 |
| Badabing_ | it doesn't need to, it's a default parameter. | 07:12.56 |
| kens | Hmmm, did I change that ? I thought the default was for jpeg | 07:13.19 |
| Badabing_ | JPEG compression (the DCTEncode filter) is used for 8-bit images that have smooth color changes (low-frequency images). The parameters specified in the ColorACSImageDict or GrayACSImageDict dictionary are used to provide further control. JPEG typically provides greater compression than Flate, but is lossy (can lose information). Flate compression is used for all other images. Flate is a lossless compression method, so it is mo | 07:13.28 |
| | that's from the documentation for the Acrobat DC SDK | 07:13.53 |
| kens | And how does that have anything to do with Ghostscript ? | 07:14.10 |
| | But anyway, you still seem to be using JPEG, not Flate | 07:14.31 |
| Badabing_ | Well you see the ColorACSImageDict stuff in there? That's essentially controlling the threshold for when it decided to use FLATE vs JPEG | 07:14.34 |
| | decides* | 07:14.45 |
| kens | Err, I don't think so, no | 07:14.52 |
| Badabing_ | Then Adobe's documentation is wrong. | 07:15.06 |
| kens | You can't assume that Ghostscript works the way Acrobat does | 07:15.11 |
| Badabing_ | Ghostscript's documentation said mainly the same thing | 07:15.19 |
| kens | That's because it was copied from teh Adobe documentation | 07:15.35 |
| Badabing_ | sec... | 07:15.38 |
| | kens: Well I have a pdf that demonstrates that an image is being compressed with FLATE rather than JPEG. | 07:15.59 |
| | while having a very small file size | 07:16.04 |
| | so I know it's working | 07:16.12 |
| kens | Hmm, well that surprises me. | 07:16.17 |
| | Of course, the JPEG compression code itself can switch to a different method. | 07:16.43 |
| Badabing_ | https://www.ghostscript.com/doc/9.05/Ps2pdf.htm#Options | 07:17.13 |
| kens | I suspect you have simply set it up so that the JPEG compressor moves to the lossless compression mode. You don't often see that in JPEG | 07:17.15 |
| Badabing_ | AutofilterColorImages, see note 1 | 07:17.22 |
| kens | Yeah AutoFilter is a different thing altogether | 07:17.52 |
| | That writes the images multiple times using different compression filters, and then looks to see which produced the smallest output, and uses that. | 07:18.26 |
| Badabing_ | "If true, the compression filter for color images is chosen based on the properties of each image, in conjunction with the ColorImageAutoFilterStrategy setting. See Automatic compression for more information." | 07:18.31 |
| kens | Besides which, that's the 9.05 documentation, the current version is 9.21 | 07:18.58 |
| Badabing_ | "You can use the ColorImageAutoFilterStrategy and GrayImageAutoFilterStrategy settings to choose between two automatic compression strategies. The value of these settings can be either JPEG (the default) or JPEG2000 (which applies only to PDF 1.5 and later files). If you choose JPEG:" | 07:19.03 |
| | "PEG compression (the DCTEncode filter) is used for 8-bit images that have smooth color changes (low-frequency images). The parameters specified in the ColorACSImageDict or GrayACSImageDict dictionary are used to provide further control. JPEG typically provides greater compression than Flate, but is lossy (can lose information)." | 07:19.14 |
| kens | Yeah I still don't see anything there that says it switches between Flate and JPEG | 07:19.43 |
| | But frankly, if you're happy with what you have, its not important | 07:19.55 |
| Badabing_ | "If true, the compression filter for color images is chosen based on the properties of each image" | 07:19.56 |
| | "You can use the ColorImageAutoFilterStrategy and GrayImageAutoFilterStrategy settings to choose between two automatic compression strategies." This leads to ColorACSImageDict... | 07:20.17 |
| | "The parameters specified in the ColorACSImageDict or GrayACSImageDict dictionary are used to provide further control. JPEG typically provides greater compression than Flate, but is lossy (can lose information)." | 07:20.23 |
| kens | Yes, thaty's the AutoFilter strategy | 07:20.28 |
| Badabing_ | ...yes, exactly. | 07:20.37 |
| | ColorACSImageDict is essentially controlling the filter. | 07:20.50 |
| kens | Its controlling the JPEG filter, it won't have anythign relevant to the Flate filter | 07:21.13 |
| Badabing_ | Images that wouldn't normally be filtered into FLATE are filtered into FLATE | 07:21.21 |
| kens | AutoFilter is true, so all images are candidates for switching | 07:22.02 |
| Badabing_ | right. | 07:22.10 |
| | I'm glad we agree? | 07:22.19 |
| kens | So really you shouldn't need to play with the ACSImageDict and so on | 07:22.22 |
| | But as I said, if you're happy, I'm not going to worry about it | 07:22.35 |
| Badabing_ | ahhh, I see what you're saying, actually. | 07:23.07 |
| kens | Note that you haven't (or don't seem to) have set DownsampleColorImages to true, so the downsampling switches won't do anything | 07:23.14 |
| Badabing_ | I think this is just making the jpegs a much higher quality | 07:23.18 |
| kens | Essentially, yes | 07:23.29 |
| Badabing_ | eh? I don't have any downsampling switches | 07:23.41 |
| | Default doesn't downsample | 07:23.44 |
| kens | One day I'm hoping to implement the 'pass through' feature so that JPEGS don't get decompressed and recompressed | 07:23.51 |
| | 'ColorImageDownsampleType /Bicubic | 07:24.11 |
| Badabing_ | oh that was a leftover I forgot to remove | 07:24.29 |
| | the other command doesnt' have that | 07:24.33 |
| kens | Though I see you removed that in the second command line | 07:24.34 |
| Badabing_ | I wish I knew where to get the JPEG2000 library | 07:25.25 |
| kens | There are plenty of places which will sell you one | 07:25.43 |
| | There are no free (compression) codecs because you need to pay the patent holders | 07:26.00 |
| Badabing_ | Really? Where is it sold? | 07:26.25 |
| kens | Well, there's Luratech that sell one | 07:26.36 |
| | THere were others, I'm sure a Google search will turn them up | 07:26.51 |
| | Kakadu still seesm to be in business | 07:27.17 |
| Badabing_ | Luratech makes you request a trial | 07:27.34 |
| kens | Is that a problem ? | 07:27.48 |
| | Like I said Kakadu is also in the business stil: | 07:28.21 |
| | http://kakadusoftware.com/ | 07:28.21 |
| Badabing_ | I just don't understand why they're not upfront about how much it would cost | 07:28.23 |
| kens | Oh well, don't know about that. | 07:28.36 |
| Badabing_ | kakadu isn't upfront about the price, either | 07:29.07 |
| kens | I guess they probably want royalties | 07:29.09 |
| | So they can't give a price | 07:29.24 |
| | Its 'possible' openjpeg allows compression, I haven't looked | 07:30.06 |
| | Apparently it does | 07:30.24 |
| | Oh there's JasPer tooo fo course, but that's just horrible | 07:31.24 |
| Badabing_ | Is Ghostscript compatible with Kakadu's implementation? | 07:31.50 |
| kens | And here's another: | 07:31.54 |
| | http://dsplab.diei.unipg.it/software/c_quick_jpeg_2000_cqj2k | 07:31.54 |
| | Badabing_ : if you wanted to add JPEG2000 compression to Ghostscript you will have to do coding | 07:32.16 |
| Badabing_ | But the make guide says if you have the source code you can just add it to their respective directories | 07:33.29 |
| | "To compile Ghostscript against the proprietary Luratech JBIG2 and JPEG 2000 implementations, simply ensure that the luratech/ldf_jb2 and luratech/lwf_jp2 containing the Luratech code exist in the top level gs source directory, and (re-)run configure (ensuring to make clean before re-running make). The configure script will detect the presence of the directories, and apply the appropriate settings in the Makefile." | 07:33.47 |
| kens | Yes, that's because we licence Lueratech commercially for our paying custoemrs. So if you have the Luratech library then you can use our existing interface for it. | 07:34.25 |
| | That's the only one we have an interface for. | 07:34.41 |
| | It also doesn't permit the use of JPEG2000 compression | 07:34.51 |
| | So you would still need to add that to pdfwrite | 07:35.00 |
| Badabing_ | but it can already read JPEG2000. | 07:35.13 |
| kens | Yes, but that's not the same as writing it | 07:35.26 |
| Badabing_ | No I mean, even without the luratech source code it can read JPEG2000 through openjpeg, so... it sounds like all this interface does is let you read JPEG2000 through Luratech's own code instead? | 07:36.14 |
| kens | Yes | 07:36.22 |
| | Because its faster and more memory efficient | 07:36.30 |
| | and has fewer bugs | 07:36.36 |
| | And if it does have bugs we can get Luratech to fix them | 07:36.47 |
| Badabing_ | Oh well. | 07:37.02 |
| deekej | hello folks, the DEFAULT_VM_THRESHOLD value set the limit when the garbage collecting starts? | 14:32.35 |
| kens | Not really, no | 14:33.39 |
| | the vmthreshold can be changed on the command line and by PostScript, that's just the default value. | 14:34.17 |
| | You can also trigger a garbage collection execution by various means | 14:34.33 |
| deekej | okay, thanks :) | 14:36.42 |
| chrisl | deekej: It would be more correct to say that DEFAULT_VM_THRESHOLD is the default value for a setting that /contributes/ to the decision of when to garbage collect | 14:36.55 |
| aidos | Does anyonw have any experience with the svg output device? It seems to have been removed - anyone know why? | 21:53.30 |
| HenryStiles | aidos: future svg output will likely happen in mupdf not ghostscript. I don't recall the history of the device, I remember it was unstable, so removed but then reinstated for a while, but anyway I recommend mupdf | 22:21.06 |
| aidos | oh ok, interesting. I use mupdf to clean / decompress pdfs so I can read / hand edit them. I hadn't noticed that it could do SVG conversion. What's the state of that? | 22:26.15 |
| HenryStiles | pretty sure it's as least as good as what gs had | 22:26.49 |
| | might want to ask on mupdf irc during european business hours | 22:27.33 |
| aidos | great. thanks for the pointers. I'll have a play and dig around in the code to see where it seems to be at. Appreciate the help. | 22:28.35 |
| HenryStiles | sure no problem | 22:29.23 |
| | Forward 1 day (to 2017/08/24)>>> | |
Log of #ghostscript at irc.freenode.net.