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Author Topic: Further thoughts on Epson ColorBase  (Read 2940 times)


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Further thoughts on Epson ColorBase
« on: February 15, 2007, 12:16:25 pm »

I'd like to share some information I've learned about Epson ColorBase and some educated guesses about its role for non-Epson papers.

In this old thread there was a discussion about ColorBase 2.0's added support for the Epson 3800 but the conclusion was that third-party papers are not supported.

Having learned a bit more about how ColorBase works and how the Epson printer drivers work, I think the conclusion should be: third party papers are supported, but not directly. Here's why.

For Epson printers like the R2400, 3800, 4800, etc., the ink settings (i.e., how much ink to put down for a device RGB value, and ink limiting) are determined primarily by the Media Type chosen in the driver settings. You can make further adjustments using the Color Density slider under Paper Configuration, but in general the main knob is the Media Type (e.g., choosing Premium Glossy, Premium Luster, Enhanced Matte, etc.).

According to Epson, the ColorBase software does not change the firmware of the printer. I quote from Epson's FAQ:

First you print an Epson ColorBase test chart. The test chart consists of 264 colour patches. After a specific drying time you measure the test chart with a spectrophotometer. Epson ColorBase compares the actual measurement result with the ideal result of a standard Epson printer and calculates the correction that has to be applied to your Epson printer in order to match the standard Epson printer. These corrections are saved in the calibration data file. The calibration data file is inserted into your Epson printer driver's look up tables (LUTs) that drive the colour halftoning process.

The calibration data are linked to a certain Epson printer serial number and black ink configuration and stored in the data folder of Epson ColorBase. When you activate the calibration data, they communicate with the Epson printer driver or Epson Stylus Rip printer driver to influence the colour halftoning process. So the calibration data are stored in the computer.

(Boldface emphasis is mine.)

It makes sense that the calibration needs to be done on a per-Media Type basis, because each Media Type setting has its own associated set of rules for how the ink is distributed.

This brings me to my main point, which is what happens if you want to use non-Epson media.

Here's my educated guess (but just a guess!) as to why using non-Epson paper doesn't work directly with ColorBase. My guess is that at the factory, Epson optimizes each Media Type setting for its corresponding paper -- for example, the Premium Luster Media Type is tied to a driver setting that will give good results on Epson's Premium Luster paper. Specifically, Epson knows that if you send the printer a device RGB triplet value of, say, (255, 0, 0), what the corresponding Lab 2-degree D50 values should be. This data (for a set of 200+ device RGB patches) is built into ColorBase.

So if you feed in a similar but different paper, such as Ilford Smooth Pearl or InkJetArt MicroCeramic Luster -- which may have different paper white values (ISP is yellower than EPL, for instance) and have different ink absorption properties --  then the printed patches won't match ColorBase's internal database of expected patches, which were built using Premium Luster paper. Hence the error that you'll get if you try to use third-party papers.

But ... this doesn't mean that ColorBase isn't useful for third-party papers. It just means that during the calibration process, you have to feed it Epson paper. After that, when you go back to doing regular printing, you can substitute your own third-party paper. Remember: all ColorBase does is write lookup table information that instructs the printer driver which colorants to emit for each Media Type setting.

So, let's say you want to use MicroCeramic Luster (MCL) and you normally use a profile created using the Epson Premium Luster (EPL) Media Type. Then if you want to use ColorBase, you need to have a sheet of EPL on hand. Once ColorBase is done, you can create a profile for MCL using the EPL Media Type. The calibration data generated by ColorBase will be applied whenever you print using the EPL Media Type. (Even though you specify EPL as the Media Type, the printer has no idea whether you are feeding EPL or some other paper like MCL when you are actually printing.) The practical benefit of this is that any other printer of the same model that is calibrated using ColorBase for the EPL Media Type can use the same ICC color profile for printing on MCL paper and get (nearly) identical results.

As stated in Michael's original article on ColorBase, this tool is mostly useful for situations where you need to ensure that multiple printers of the same model perform the same way. But it can also be useful for a user with a single printer, just to make sure that the printer is generating proper ink loads. Even though a good custom profile will fix small problems, it's better to start with a properly linearized printer, which can help lead to a smoother profile.
Eric Chan
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