Graphics Muse

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Musings

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© 1996 Michael J. Hammel
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Printer Info


      My old Epson 3250 printer served me well for the 2 years I used it. It still works, but the graphics capabilities are limited and the printer only supports black and white printing. I'll probably give it to my nephews when they get a computer next month. I packed it up in December and set out to find a color printer. Why? Because I didn't have one. I wasn't sure what I'd do with it, but I wanted one.
      The first step was to start looking for what the current state of the art was - what kind of printers are available now. Ink Jet printers are all the rage for desktop users, apparently, due to their low cost and high quality color output. I asked around on a few mailing lists and got a pointer to some reviews of printers in PC Magazine Online. I scanned these looking for basic information on what features each supported and the price ranges I would be looking at when I went shopping. However, before I could choose a particular printer I had to know what printers Linux could support. And printer support on Linux is primarily supported through the use of Ghostscript.
      Printers all speak a language of some sort for determining how to print the data that is sent to them. Some printers, mainly laser printers, can speak Postscript directly. Most inkjet printers have their own specialized languages, such as the ESC/P2 language that EPSON printers use. Ghostscript is a package that provides drivers that speak the printer language for a large number of printers. It takes a Postscript file as input and outputs it in a format suitable for the display device (which can be a printer or even an X display). This means you have to turn your images into Postscript before feeding them to Ghostscript. This can be done using the ppmtops tool from the NetPBM package.
      I found the Ghostscript Web site by searching the Yahoo GNU Software section. This site provided me with information on the latest version of the package, the Aladdin Ghostscript 4.03 package. The Aladdin version of Ghostscript is freely available for private use but cannot be distributed commercially. There is a GNU version as well, but the fonts delivered with the Aladdin version are much better. This is a rather large software package, but it builds fairly easily. What was most important to me was finding out which devices are supported. Fortunately, these are listed in a file called devices.txt in the source distribution. Some of the devices supported include: With this file in hand I returned to the PC Magazine printer review and scanned the list of printers. Some things I noted while researching printers in the review:       I decided on the Epson Stylus Color 500 due in part to its rather glowing review and the fact that it was listed under $300. It was not specifically listed by the devices.txt file in the Ghostscript package, but I found a Espon Stylus Color 500 Web site hosted by Alan Williams which provided a wealth of information regarding this particular printer. I stumbled upon this page from the Printer Compatibility page of the Ghostscript Web site. The Printer Compatibility page does specifically list the Epson Stylus Color 500 as a supported device. If anyone is interested, the printer specifications are availabe from www.epson.com under the Corporate Products page.
      I purchased the printer, took it home and immediately unpacked it (I was trying to get it set up prior to a two week Christmas/New Year's vacation). Printer setup is pretty simple. Don't bother with the MSWindows configuration stuff. Just follow the printed steps for unpacking the printer, installing the ink cartridges, and running the self test. I had to do a bit of tweaking of the stcolor.ps file (a Postscript file that must be printed first to set up the printer prior to each of your files) to fit an image on a greeting card, but in general this should be necessary. In fact, my solution (tweaking stcolor.ps) doesn't work quite right. If anyone figures out how to print offcenter using the stcolor.ps configuration please let me know.
      Alan has some scripts for printing in various modes (low quality draft to high quality) but neither he nor I use printer filters. These are scripts or other programs which read from standard input and determine how to process the file. If you don't use any filters then you can use lpr to print an output file produced from gs (Ghostscript) directly to the printer. On my system I still just redirect the output to /dev/lp, but I'm the only person using my Linux system. In fact, I spent most of my time working on a script that would print TGA and GIF images by converting them to Postscript and passing them to gs to be printed directly to /dev/lp. If anyone is interested in this script I can send it to you, but its a hack at best. A printer filter would probably be better.
      If you are interested in adding filters you can try either apsfilter or magicfilter, both of which are buried in the Sunsite archives and probably the tsx-11 archive as well. Red Hat 4.0 doesn't use these due to packaging considerations. Apparently at least one of them requires that you install the C compiler in order to print. Not very useful to non-developers who simply want to print graphics or text (ie just use Linux, not develop on it). If its true one (or both) of these packages has this requirement then I whole heartedly agree with Red Hat's decision. Red Hat 4.0 has its own printer facility but I've heard its not all that spectacular. I've been told by folks at Red Hat that the next version (which I believe is currently being used in-house) will be much better.
      The Epson Stylus Color 500 is the printer to get if you just want to create some nifty labels, Christmas cards, or menus for a restaurant and have a limited budget for printer hardware. Its support of transparencies makes it nice for some of the X Windows development I'm doing at work where I need to write a specification and provide a simple class on the design of the application I'm building. However, this printer is not quite good enough for high quality prints of photos or 3D renderings. These might come out fairly well on the glossy inket paper, but normal inkjet paper wrinkles with high-color images and the image comes out rather grainy. Even so, for simple home or small office use, the Epson Stylus Color 500 is a good printer that is supported through Ghostscript that is reasonably price.
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tkPOV V2.0


      The Persistance of Vision Ray Tracer, more commonly known as POV-Ray, is a tool for creating photorealistic images. The Unix versions, including the Linux port, provide for interactive display of the image being rendered in an X window, but there is not graphics interface built into the program. It is started with a command line that supports a large number of options. Although the tool is quite powerful in its ability to render complex scenes, the lack of a graphical front end means that many of the more useful features are seldom used by the casual user. Graphical front ends to POV-Ray are available on the MS Windows port, however.
      Recognizing the limitations of a command-line oriented interface, a group of students at the University of Minnesota decided to make create a graphical front end to POV-Ray as a class project in User Interface Design. The result is tkPOV, a Tcl/Tk/Tix program that allows users to select and set various options to POV-Ray. The current version of tkPOV is 2.0 beta1 which reportedly supports versions 1.x, 2.x, and 3.0 of POV-Ray. I don't have the older versions so I examined the application using POV-Ray 3.0. tkPOV requires Tk 4.0 or later, Tcl 7.4 or later and Tix 4.0 or later and is covered by the Artistic copyright. I'm not familiar with copyright laws, but this appears to be a fairly permissive copyright. There is no charge for personal or other use as long as the rules of the copyright are followed.
      The installation of the source is very straight forward. There is a Makefile that requires a change to one variable when installing from the source distribution. I changed DEST_DIR to /usr/local/bin. I also had to make some minor changes to the rules for making tkpov-src, which is the rule to use when installing from the source distribution. Rather than explain them, since the rules are fairly simple, I'll just provide my version: 
tkpov-src: tkpov.test Makefile
   rm -f tkpov
   echo "#!/bin/sh" > tkpov
   echo "# -*- tcl -*- \\" >> tkpov
   echo exec ${WISH} \"\$$0\" \"\$$@\" >> tkpov
   cat tkpov.tcl >> tkpov
   chmod 755 tkpov
The changes were required since a newline was not being printed by the echo command in the original version. After you've made the changes you simply run
       make tkpov-src
and the package should be installed in whatever directory you specified in the DEST_DIR variable. Note that if, like me, you used /usr/local/bin as the destination directory you'll probably have to run the make command as the root user.
tkPOV Figure 1
Figure 1: Main Window, with General tab displayed
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Once the application has been installed you can begin exploring. Type
       tkpov
and a rectangular window opens up with a series of 5 folder tabs (see Figure 1). The first tab, labeled Info is the obligatory credits and contact information. The second tab, labeled General, provides a set of input fields for specifying input and output files. There are a number of pull down menus as well which allow the user to select image size, output file format (PNG, PPM, TGA, and Compressed TGA), and image quality. The pull down menu for image quality is nice in that it not only shows the numeric levels that can be used but also gives a short (one or two word) description of what you'll get using that level. Note that lower levels of quality render faster and can be used to test object positions or other features of your scenes without having to wait for POV-Ray to calculate textures or halos. Textures and halo calculations can be very time consuming. The Input File field is accompanied by a file folder button which brings up a file selection window. The user can also simply type in the path to a file in the input if so desired. Once an input file is selected a default output file name is displayed in the Output File window which is based on the input file's name and path along with the output file type.
      The General Tab window is the main window for starting a render. A button is provided that, when clicked on, will attempt to start the POV-Ray renderer using options specified in the other tab windows, which we will examine in a moment. Also, an editor button is provided that allows the user to call the editor of their choice (configured under the Config tab) to make updates to the selected input file. Unfortunately the stock code for this feature appears broke since no matter how I configure the editor it always complains it can't find emacs (even if I tell it to use vi or xedit). Lastly, this window provides a button for exiting tkPOV, labeled Quit.
      Ok, so now you have a selected an input and output file and decided that it will be a PNG output file rendered at 640x480 using the highest quality setting. Before we render we'll want to configure some of the command line options for POV-Ray. Lets take a look at the next tab, Antialias. Again, the Render, Editor, and Quit buttons are available.
tkPOV Figure 2
Figure 2: Antialiasing options
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New to this window is the button which defines whether Antialiasing is turned on or off. By default it is off and the button displays a message stating what will happen if it is pressed (not the current state, which can be a little confusing at first). Pressing the button causes a number of new fields to be displayed. The levels of Jitter, Alias Threshold, and Ray Grid Size can be set by typing in a value or using the slider bars provided. Jitter is turned on by default and can be turned off by clicking on its toggle button. On the other hand, Adaptive Antialiasing is off by default and must be toggled on if needed. For our little example lets say we want a high quality image. We'll turn on Antialiasing, which allows the smoothing of the jagged, "stair step" look of diagonal lines in computer generated images. The aliasing threshold we set, somewhat randomly, to 0.35. We'd also like to reduce the amount of time it takes to render our image. The Jitter option, which allows POV-Ray some randomization while doing its antialiasing in order to smooth jagged edges even further, can add to the compute time of a rendering. We'll leave that value turned off.
      Since I've not really examined all the options available with POV-Ray 3.0 I can't comment on the usefulness of the advanced options. Interested readers should consider examining the POV-Ray 3.0 documentation at the POV-Ray web site.
tkPOV Figure 3
Figure 3: Configurable Parameters to tkPOV
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      Now you're ready to render your image - except that you haven't told tkPOV where to find the POV-Ray binary! Under the Config tab are fields for specifying the name of the binary (which has changed from version to version), the path to the directory that contains the various POV-Ray include files and the editor of choice. There is also the ability to turn the interactive display of the rendering on or off. I like to leave this on while testing. You can save these settings with the Save button. The saved values are placed is a dot file named ".tkpov2rc" in the users HOME directory.
      Now you're ready to return to the General tab and start the render. With luck, after a reasonable time you'll have a beautiful new image. tkPOV won't help you create better scenes, but it will give you a little more control over the rendering process using POV-Ray. Its been awhile since I last used the 3.0 release of POV-Ray and I seem to remember there being many more options. I could be wrong, and since I was crunched for time to get this months column out I wasn't able to spend as much time researching such issues. But I can say tkPOV's interface appears to be easy to use and a convenient way to run my test renderings. I can throw away my old bash scripts now and just leave tkPOV up in one of the many pages I keep in my fvwm desktop.
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© 1996 by Michael J. Hammel