Digital Darkroom

GrayScales
B&W From A Color Printer

Darryl C. Nicholas  |  Feb 1, 1999

Figure 1.
Original color image printed as an RGB tile on Epson Stylus 1520 ink jet printer.
Photos © 1999, Darryl C. Nicholas, All Rights Reserved

A few years ago the manufacturers of ink jet printers were struggling in order to make printers that could lay down very tiny dots--very close together. During those days if you tried to make a black and white print, it tended to look a little grainy compared to color prints made on the same printer. To deal with the problem, most of us would convert the black and white image file back into a RGB film, then send the image file to the printer as a RGB file. The printer would use all four of its inks (Cyan, Magenta, Yellow, and Black--CMYK) to print the image. By using four inks, the printer would lay down more dots and the dots were closer together than if the printer had attempted to print the same image using only black ink. This resulted in an image that had smoother tone gradations and less grain. The only problem was in getting a pure neutral, black and white image. When a black and white image is created using colored inks, it is necessary to have the printer calibrated absolutely perfect. If the printer is the least bit out of calibration, the black and white image will have a slight color cast. Such a slight color cast might go unnoticed in a color picture, but in a black and white picture even a slight color cast becomes noticeable. Still, it was only a couple of years ago that printing black and white images with color ink was the best way to get the best quality image.

Figure 2.
Same image converted to "grayscale" then, converted back to RGB for printing.

We do a lot of restoration work and sometimes customers want black and white prints as well as sepia-toned prints. If we group black and white and sepia-toned prints on the same 8x10 sheet, we print the whole thing as a RGB file. In such a case, the black and white images that are on the sheet are created with colored inks--just like in the "old" days--a couple of years ago. Be careful using this technique. Some ink jet papers have coatings that absorb the four inks (CMYK) at different rates. This means that after such an image has "cured" for a few days, one of the four inks might continue to soak into the coating more than the others, which can cause a slight shift in color balance two or three days after the print was made. I'm only talking about a shift in color of 2-3cc, but such a shift will show up in a black and white print.

Today, we are using Epson Stylus ink jet printers. We have model 1520 and model 850. The 1520 can print up to 13x20", while the 850 can print only up to 8x10". Both printers use the same ink cartridges, produce the same quality, and print at about the same speed. These printers utilize some of Epson's most recent technology, allowing them to lay down very tiny dots very close together. Because they can lay down such tiny dots, they are able to make a picture from only black ink and make it look as smooth in tone value as the color prints are. See Figures 1, 2, 3.

Figure 3.
Same image converted to "monochrome" image using only black ink.

Ink jet printers do the things that they do because of the special software that comes with them called a "driver." Not all printer drivers are created equal. There are vast differences between drivers for different brands and models of printers. Generally speaking the "better" printers ($300 and up) have better drivers. Figures 4 and 5 show the options that the driver for the Epson Stylus 1520 printer offers. Notice in Figure 5, I have set the slider-bars for specific values. This is how I "calibrate" my printer to my monitor, so that what I see on the monitor is what I get from the printer.

A good driver will allow you to fine-tune the quality of the printing by letting you adjust the color balance, contrast, density, and saturation. Such drivers will allow you to turn off the color ink and use only the black ink, while still printing in the "photo quality" mode. I have seen drivers that would force you to print with colored inks if you were in the photo quality mode. Those drivers would only allow you to use "black only" ink if you were in the "letter" mode.

There are several different types of image file formats--RGB, CMYK, gray scale, and a few others. I use Adobe's Photo-shop (Version 5.0) for all of my graphic work. Photoshop makes it easy to convert a color image to black and white (grayscale) and then back to RGB if you need to. CMYK is a special format that is used by folks who are working with a lithographic (offset) printer. Never send a CMYK file to an ink jet printer. Yes, it will print, but the quality and color balance will not be very good. Always be sure that any color files you send to an ink jet printer are in RGB form. If you are sending files of black and white pictures to an ink jet printer, the file must be in RGB or, if your printer driver can handle it, grayscale.

Figure 4.

If you are converting a color picture to a grayscale image, Adobe's Photoshop will perform the conversion automatically for you using a predetermined set of gray values for the various colors.

For example, the automatic conversion uses a mixture of about 59 percent of the green channel, 30 percent of the red channel, and 11 percent of the blue channel. Adobe thinks this mixture produces the best quality image most of the time.

However, if you don't care for the results of the automatic conversion, Photoshop allows you to customize the value settings almost any way you want. Simply go to the channels window in Photoshop and click on one channel and then another. Compare the varying tonal distributions between each of the RGB channels.

Figure 5.

Highlight the channel with the most pleasing distribution of tone values and convert to grayscale by going to Mode: Grayscale. When the "discard color information" dialog box appears, click on OK. It is also possible to combine the effects of two or three different channels, in a different ratio from the Adobe automatic selection noted above, but the explanation for how to do it is a bit lengthy for this article.

If you'd like additional help with ink jet printing problems, you can write to me care of Shutterbug magazine or send e-mail to colorbat@desupernet.net.

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