A Site for Photographers by Photographers

Featured Equipment Deals

Macro Flower Photography: A Tutorial in Focus Stacking Read More

Macro Flower Photography: A Tutorial in Focus Stacking

Editor's note: This excerpt first appeared in photographer and author Harold Davis' recent Focal Press book, Photographing Flowers: Exploring Macro Photography with Harold Davis. The closer you...

Latest Equipment Articles

Choosing a Mobile Photo Printer Read More

Choosing a Mobile Photo Printer

In today's mobile, digital world, we carry hundreds or even thousands of pictures around on our smartphones and tablets. Tom Persinger looks at 4 different mobile photo printer options for getting...

Latest Learning Articles

Advanced Printing with Lightroom (Video Tutorial) Read More

Advanced Printing with Lightroom (Video Tutorial)

Building upon last week's Basic Printing with Lightroom video tutorial, this advanced printing tutorial will teach you to print contact sheets, print multiple images at a time, use Lightroom's present...


Photoshop 18 Percent Grey

Jim Vanson , Jul 20, 2003; 02:58 a.m.

Does anyone know what the PhotoShop settings for 18 percent Grey are?

Responses

Leonard Evens , Jul 20, 2003; 09:29 a.m.

It depends on what you mean by 18 percent gray, If you take that to be middle gray and make plausible assumptions about the gamma of the monitor, then in principle you should take the middle values for RGB, i.e, R=G=B=127 fo a scale of 0 to 255. But that is unlikely to look on the screen like a gray card you hold up next to it under normal lightling. The card is likely to look darker. Also, if you print normally, you are not going to get something that looks like the gray card.

The math goes as follows. The native gamma of a typical CRT is 2.5. The light intensity on the screen is roughly the relative value raised to the gamma power. 127/255 ~ .5, and .5 raised to the 2.5 power is about .18 or 18 percent. However, the human visual system tends to exaggerate responses based on viewing conditions. For viewing a TV screen or monitor, there is an adjustment for gamma to compensate for this, so one is usually advised to set a PC monitor's gamma to 2.2. Since .5 to the 2.2 is about 22 percent, that is brighter than the expected 18 percent, but if you are looking at a step wedge on the screen and want the .5 value to appear to be in the middle, you are better off with the smaller gamma.

At least this is what I've managed to glean from reading Poynton and other technical notes on the subject.

Jim Vanson , Jul 20, 2003; 02:29 p.m.

Excellent reply...tkx Leonard...jim

Kevin Connery , Jul 20, 2003; 05:32 p.m.

The gamma of the color space used ("working space") will have a large effect. 127R, 127G, 127B in sRGB is significantly different than 127/127/127 in ColorMatch or ProPhoto RGB, and a tiny bit different than in Adobe RGB (1998).

The gamma of the display itself should be corrected out by Photoshop's internal color management, and shouldn't have any visible effect, if it's working properly and the display is calibrated.

Back to top

Notify me of Responses