GPLin 0.0.1-pre6 released

2009-03-29

Here's another preview of GPLin - several behind-the-scenes changes this time, and the ability to deduce a suitable ink limit for each channel automatically.

The PrintDeviceN utility will take these limits into account when printing.

GPlin-0.0.1-pre6.tar.gz

GPlin-0.0.1-pre6.zip

(WARNING: the Win32 build is highly experimental and is almost certainly buggy and crash-prone.  Please note also that it makes use of the Gutenprint printer driver system, and CANNOT make use of native Windows printer drivers.)

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Here's a rough step-by-step guide to using GPLin in its current form:

Having built with the usual ./configure && make commands:

• At the shell prompt, type: ./gplin
• Enter a filename for the project on the first page of the user interface
• On the second page, choose your printer queue and preferred settings.  I would recommend the following:
  • On the first pane, set Channels to Composite CMYK.  (Raw printer channels works, but is of limited use in the absence of software to perfom DeviceN profiling)
  • Colour Correction should be set to "Raw".  This disables all of Gutenprint's own ink limiting and linearization, leaving everything to GPLin.
• On the next page, choose a suitable starting density - and print a Density Evaluation strip,   Err on the side of caution when choosing the starting density - if this is too high you stand a good chance of flooding the inside of your printer with ink!  On my R285 at 1440x1440dpi on lightweight inkjet paper, 0.25 is about right.  Note also that if you're going to use a total ink limit when profiling of 200% you need to reduce this density to 50%.  If you want to use an ink limit of 300%, reduce it to 33%, and so on.  I'm currently looking at ways of solving this problem.
• The next page, choosing a suitable base gamma, isn't crticial in terms of accuracy - it simply improves the distribution of the test patches at the linearization stage.
• Next is the Test Chart Generation step - where you choose the number of patches per channel.
• Finally, printing the page(s) of test patches.

The next step, reading in the printed test chart, is currently not supported within GPLin - you will have to perform this step manually using Argyll's chartread command.  The needed .ti1 and .ti2 files will be found in the <projectname>_temp/ directory.

Once you have a .ti3 file from ChartRead, you can use the Channel Ink Limits page to set a suitable ink limit for each channel.  GPLin will use the hue deviation which occurs as paper becomes saturated to determine a suitable default ink limit for each channel - a technique suggested by Graeme Gill.

The last step currently implemented is selecting a suitable total area coverage for CMYK profiling.  This is performed once again by printing a sweep pattern and reading off where the paper starts to saturate.

 

Finally, there's a utility provided with GPLin, called "printdevicen".  This can be used to print CMYK or DeviceN images using the linearization curves from a GPLin project.

To use it, simply invoke from the command line with:

./printdevicen -p <projectname>.gplin filename.tif [filename.tif ...]

Printdevicen will automatically find and use the .ti3 file to generate correction curves, and will use any channel ink limits saved in the project.