Under Development: Multitoner Tool
Motivation
Silber & Blei will produce exclusively with FLOS-Software. Because it’s important to us to have control over our tools. We’ll make first class print products with free software. The consequence of this decision is that we write missing software ourselves. A program to create multitone images is missing in the free software world so far. The Multitoner Tool will be released under the GPLv3.
What is Multitone
When offset printing black and white images with just one ink—black in the standard case—the results appear dully and without depth. That’s because one color channel in printing can render ca. 50 differnt shades, see: Gamut. For comparison: a black and white image on a computer monitor is rendered with ca. 256 shades. To print black and white images in high quality, so that they show a depth comparable to a photographic print, multiple inks are used for one image. For instance: black for deep tones and gray for mid-tones. The gamut of the result can be increased depending on the count of the used colors.
Terms
When one ink is used it’s called “monotone”, with two inks it’s “duotone”, three is “tritone” and four is “quadtone”. The whole topic is summarized with “multitone”.
The Tool
The core function is setting up the inks that are going to be used (up to ten), where there is a control curve for each ink. The curve assigns for every input value—from black to white–the quantity of the ink to print— from full application to none. There are diffrent curve types to interpolate between the control points: linear, cubic splines, monotone cubic splines.
The inks are getting a name, to identify them clearly later in the process. CMYK-values are assigned for the screen preview. The order of the inks can be varied, this is needed because it affects the print result.
For preview a color stripe is shown for each ink. It displays the output value after application of the control curve. A further color stripe visualizes the combination of all inks. Also, there is a preview image with the settings applied to it.
Technical Notes
The tool is written in Python. The GUI implemented with GTK+. The control curves are calculated with SciPy and NumPy. The widget for display and manipulation of the control curves is self-made (as GtkDrawingArea). Color preview and preview image are rendered using Ghostscript. Colormanagement shall be achieved through Ghostscript in the future.
Roadmap
Here a rough scatch on how I conceive the projects further progression:
- current status: the core functions are implemented
- loading and saving of projects
- creation of multitone-EPS-images from black and white images with commandline tool and GUI
- cleanup, more code comments, licence notices, README
- publication of the repository
- public testing and first production uses
- Color management: (research and implementation) to obtain optimal previews ICC-profiles shall be used in future. See also the option ‑sDeviceNProfile in the Ghostscript manual and GS9_Color_Management.pdf.
- better batch processing and handling of exceptions there: different curves for the same set of colors