|
 |
Quick Find |
 |
|
|
|
Categories |
|
|
|
|
Information |
|
|
|
|
| 
Grayscale vs. Desaturate
for Black and White printing
Many photographers getting into digital printing want to make black and white prints of their color images. There are two main methods (see note 1) of making a monochrome image from a color image: desaturating the image and converting to grayscale.
From talking to people on the phone about printing black and white images, it seems that the majority of people are using the "desaturate" method. I don't know if this is due to it being one less step than the other method, or if some Photoshop teacher is telling people to do it that way.
To use this method, you go to the "Image" menu, then to "adjust" and select "desaturate." Your image is still in RGB mode (you should never use CMYK if you are printing photos on an Epson inkjet - see note 2) and you can now print your image in "color" and be able to take advantage of the extra smoothness that it allows (as opposed to printing with the black ink only - see note 3). The problem with using the desaturate method is that it does not properly convert the colors into luminance, representing how light or dark it should be.
The other method involves you going to the "Image" menu, then to "Mode" and selecting "grayscale." Photoshop asks you if you want to discard the color information, hit "OK." Now go back into the same menu and select "RGB color" to convert the grayscale image back to color.
Oddly I've found the best way to illustrate this effect is with a yellow cartoon character, Homer will work nicely. I doubt anyone will argue that using desaturate on the image above is a very bad idea.
The thing to notice about the bars above is how the desaturated bars look exactly the same
I doubt anyone is using images that look like this, but is proves a point: when you use desaturate, any colors with the same bightness will end up the same shade, regardless of what color they are or how bright they appear to our eyes. In theory this is the way color should work, but in practice yellow and green are brighter than blue to our eyes.
Desaturate |
Original |
grayscale |
The bars above are from Bill Atkinson's LAB test target, and show what we're talking about very well, especially in the center of the color ramps.
Desaturate | 
Original | 
grayscale |
Notice the sky of the arch and the yellow and green in the fractal pattern. Overall, the desaturated image has less contrast then the grayscale image.
Desaturate | 
Original | 
grayscale |
Lastly we have a real image. The differences can sometimes be subtle but they're there.
So in conclusion, using "desaturate" is a poor choice if you want to retain the real look of your image. Your best option for keeping your image looking the way they should be is to use the grayscale mode.
Note 1: There are actually three additional methods, but they aren't used much. The first one is a little redundant as it gives you the same results as converting to grayscale. You can convert your RGB image into the LAB color space and discard the other channels besides luminance. The second method is actually pretty handy, but most people don't know you can use it. In Photoshop 7 and 8 you can bring up "Print with Preview" where you can select which color space you want to use for printing the image you are working on (it's in the print box on 5 and 6). Mostly this is used by people who want to use a custom ICC profile, but you can also select "Grey Gamma 1.8" or "Grey Gamma 2.2" (it's darker overall than 1.8) and your image will be converted to grayscale as it is printed. You might need to select "no Color Adjustment" in the printer setup, though, depending on your printer/ink/paper setup if you get color casts. The third method is the Channel Mixer, but that's a different topic entirely.
Note 2: People sometimes get confused and think that their inkjet printers would work best with CMYK images, being that they use Cyan, Magenta Yellow and Black inks ("k" is used for black to avoid using "b" which might be understood as blue). The problem with this is that most Inkjet printers, and especially all Epson printers, do not use the same colors as a typical CMYK printing press. The Cyan, Magenta and Yellow inks on inkjet printers are much brighter and have a larger color gamut. With many of the newer printers, you now also have additional colors: Light Cyan, Light Magenta, Light Black, Red, Blue, some even have Orange and Green inks! These additional colors extend the color gamut of the printer even further. If you limit yourself with CMYK files you are throwing away that additional color information and also setting yourself up for posterization, so just don't do it.
Note 3: With a regular color printer, you have two options for printing black and white: just print with the black ink only which guarantees that you will get absolutely neutral prints, and printing a grayscale image in color. The advantage of printing a grayscale image in color is that your printer uses all the other colors to make smoother transitions so you get a better image with less visible dots. The down side is that if your printer is not setup for a particular paper correctly, you may get green shadows and red mid-tones (or vice versa) due to the way that the paper's coating absorbs the colors differently. One last note about printing with the black ink only: it really means black only. On the newer UltraChrome Epson printers like the 2200, 7600 and 9600 which have a Light Black ink color, it does not use the Light Black when you select Black only. I only know of one way to use the Black and Light Black without using the other colors and that's by using the ColorByte RIP software which costs nearly as much as the printer.
--Chris Bair, Webmaster
|
Tracking
My Account
Cart Contents
Checkout
Home page
Forum
Contact us
Links
Newsletter
Finishing