Confused about gamma

I have been reading quite a bit about system calibration of color and I have read about the effects of gamma in relation to CRT monitors. I thought that gamma was only related to monitors....but then I read in my printer manual (Epson 870) that it has a default gamma of 1.8. I'm confused. Isn't gamma only an issue with monitors? Can anyone help clear this up for me. Many thanks in advance.--Griz

Here's the executive summary:

1. Gamma is an extra brightness boost to the midtone values of an image file. This practice originated with the advent of CRT television tubes decades ago. CRT tubes have an inherent dip in their signal-response curve, so the midtones need to be lightened in order to make images look real. Even though LCD displays have a linear response, they're designed to mimic a CRT.

2. Intel/Windows computers generally use a large gamma correction of 2.2, and up to 2.5 on older machines. Macs use a less extreme gamma which is supposed to be 1.8, but might be 1.5 before calibration. Photos will look much lighter on a Mac than on a PC.

3. Gamma correction is used for all Mac and PC imaging hardware--otherwise output would never be close to your monitor image. When Epson says their printer has a default gamma of 1.8, they're implying that the printer output should match your monitor when the monitor is set to gamma 1.8. If they made the printer response linear (gamma 1.0) then prints from Windows and Macs alike would be extremely dark compared to the monitor image. My experience is that printer response varies widely between brands, models, and even individual units. Your printer is probably much farther from ideal calibration than your monitor--so you should calibrate your monitor first, then fiddle with your printer-driver to get your prints to match your screen image.

4. You can use software such as Adobe Gamma, which comes with Photoshop and Illustrator to change the gamma of your machine by modifying the video look-up table. Software supplied with newer video cards can also usually change the system gamma.

Good luck,
Fred

Griz said:

I have been reading quite a bit about system calibration of color
and I have read about the effects of gamma in relation to CRT
monitors. I thought that gamma was only related to monitors....but
then I read in my printer manual (Epson 870) that it has a default
gamma of 1.8. I'm confused. Isn't gamma only an issue with
monitors? Can anyone help clear this up for me. Many thanks in
advance.
--
Griz

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