TOPIC: IMAGEMAGICK
Converting from CGM to Postscript
24th November 2009One thing that I recently had to investigate was the possibility of converting CGM vector graphics files into Postscript and from there into PDF. Having used ImageMagick for converting images before, that was an obvious option. However, that cannot process CGM files on its own and needs a delegate or helper application as well. This is the case with raw digital camera files too, with UFRaw being the program chosen. For CGM images, the more obscure RALCGM is what's needed, and tracking it down is a bit of an art. Though the history is that it was developed at the U.K.'s Rutherford Appleton Laboratory, it appears that it was left to go off into the wilderness rather than someone keeping an eye on things. With that in mind, here are the installation packages for Windows and Linux (RPM):
RALCGM is a handy command line tool that can covert from CGM to Postscript on its own without any need for ImageMagick at all. From what I have seen, fonts on graphical output may look greyer than black, but it otherwise does its job well. However, considering that it is a freely available tool, one cannot complain too much. There are other packages for doing vector to raster conversion and the ones that I have seen do have GUI's but the freedom to look at for cost software wasn't mine to have. The required command looks something like the following:
ralcgm -d PS -oL test.cgm test.ps
The switch -d PS uses the software's Postscript driver and -oL specifies landscape orientation. If you like to find out more, here's a PDF rendition of the help file that comes with the thing:
A certain lack of speed
2nd November 2009A little while, I encountered a problem with ImageMagick processing DNG files in Ubuntu 9.04. Not realising that I could solve me own problem by editing a file named delegates.xml, I took to getting a Debian VM to do the legwork for me. That's where you'll find all the commands used when helper software is used by ImageMagick to help it on its way. On its own, ImageMagick cannot deal with DNG files, so the command line variant of UFRaw (itself a front end for DCRaw) is used to create a PNM file that ImageMagick can handle. The problem a few months back was that the command in delegates.xml wasn't appropriate for a newer version of UFRaw and I got it into my head that things like this were hard-wired into ImageMagick. Now, I know better and admit my error.
With 9.10, it appears that the command in delegates.xml has been corrected, only for another issue to raise its head. UFRaw 0.15, it seems, isn't the speediest when it comes to creating PNM files and, while my raw file processing script works after a spot of modification to deal with changes in output from the identify command used, it takes far too long to run. Since GIMP also uses UFRaw, I wonder if the same problem has surfaced there too. However, it has been noticed by the Debian team, with the outcome being that they have a package for version 0.16 of the software in their unstable branch that looks as if it has sorted the speed issue. However, I am seeing that 0.15 is in the testing branch, which tempts me to stick with Lenny (5.x) if any successor turns out to have slower DNG file handling with ImageMagick and UFRaw. In my estimation, 0.13 does what I need, so why go for a newer release if it turns out to be slower?
Taming raw images with ImageMagick: A virtual workaround for Ubuntu 9.04
5th May 2009While using a command line tool like ImageMagick for image processing may sound a really counter-intuitive thing to do, there's no need to do everything on a case by case interactive basis. Image resizing and format conversion come to mind here. Helper programs are used behind the scenes too, with Ghostscript being used to create Postscript files, for example.
The subject of helper programs brings me to an issue that has hampered me recently. While I am aware that there are tools like F-Spot available, I am also wont to use a combination of shell scripting (BASH & KSH), Perl and ImageMagick for organising my digital photos. My preference for using Raw camera files (DNG & CRW) means that ImageMagick cannot access these without a little helper. In the case of Ubuntu, it's UFRaw. However, Jaunty Jackalope appears to have seen UFRaw updated to a version that is incompatible with the included version of ImageMagick (6.4.5 as opposed to 3.5.2 at the time of writing). The result is that the command issued by ImageMagick to UFRaw - issue the command man ufraw-batch to see the details - is not accepted by the included version of the latter, 0.15 if you're interested. It appears that an older release of UFRaw accepted the output device ppm16 (16-bit PPM files) but this should now be specified as ppm for the output device and 16 for the output depth. In a nutshell, where the parameter output-type did the lot, you now need both output-type and output-depth.
While I thought of decoupling things by using UFRaw to create 16-bit PPM files for processing by ImageMagick, it was to no avail. The identify command wouldn't return the date on which the image was taken. Though I even changed the type to 8-bit JPEG's with added EXIF information, no progress was made. In the end, a mad plan came to mind: creating a VirtualBox VM running Debian. The logic was that if Debian deserves its reputation for solidity, dependencies like ImageMagick and UFRaw shouldn't be broken, and I wasn't wrong. To make it work well, I needed to see if I could get Guest Additions installed on Debian. Out of the box, the supported kernel version must be at least 2.6.27 and Debian's is 2.6.26, so additional work was on the cards. First, GCC, Make and the correct kernel header files need to be installed. Once those are in place, the installation works smoothly and a restart sets the goodies in motion. To make the necessary shared folder to be available, a command like the following was executed:
mount -t vboxfs [Shared Folder name] [mount point]
Once that deed was done and ImageMagick instated, the processing that I have been doing for new DSLR images was reinstated. Ironically, Debian's version of ImageMagick, 6.3.7, is even older than Ubuntu's, but it works and that's the main thing. Since there is an Ubuntu bug report for this on Launchpad, I hope that it gets fixed at some point in the near future. However, that may mean awaiting 9.10 or Karmic Koala, so I'm glad to have this workaround for now.
Harnessing the power of ImageMagick
26th October 2008Using the command line to process images might sound senseless, only for the tools offered by ImageMagick certainly prove that it has its place. I have always been wary of using bulk processing for my digital photo files (some digitised from film prints with a scanner) but I do agree that some of it is needed to free up some time for other more necessary things. With this in mind, it is encouraging to see the results from ImageMagick and I can see it making a major difference to how I maintain my online photo gallery.
For instance, making thumbnail images for the gallery certainly seems to be one of those operations where command line bulk processing comes into its own, and ImageMagick's own convert command is heaven sent for this one. For resizing images, all that's needed is the following:
convert -resize 40% input.jpg output.jpg
Add a spot of further shell scripting and even a dash of Perl and the possibilities for this sort of thing become clearer, and this is but the pinnacle of the proverbial iceberg. The -rotate switch will do what the name suggests, while there are a whole plethora of other options on tap. So long as you have Ghostscript on your system, conversion of graphics to Postscript (and Encapsulated Postscript too) and PDF files is possible with the -page option controlling the margin around the image itself in the resulting outputs. Unfortunately, portrait is the sole orientation on offer, yet a bit of judicious post-processing will turn things around. Here's a command that'll do the trick:
convert -page 792x612+72+72 input.png ps2:output.ps
For retrieving image metadata like its resolution and size, the identify command comes into play. The -verbose option invokes the output of all manner of image metadata, so using grep or egrep is perhaps advisable, especially for bulking processing with the likes of Perl. Having the ability to stream image metadata makes loading databases like MySQL less of a chore than the manual data entry that has been my way of doing things until now.