After that last color theory post on value I decided that I’d like to add a few more examples to the value discussion.
First I want to talk about the value of color. Just because you have the darkest shade of a color doesn’t mean that it’s a dark value.

In this photo I have pulled the darkest value of the rainbow colors. It’s easy to tell that the blue and purple are dark values and the yellow and orange are light values. But what about the red and green?
Of course they are really both medium values but which is darker? If I had fabrics this close in value I might convert them to gray to see the true value. This is where my second lesson comes in.
Using your photo editor to determine value isn’t always right.
I know I talked about using black and white images to check the comparative value of fabrics. My Photoshop software has several methods for converting a photo to black and white. Here’s the above photo converted using different filters:

This setting is the default for the “Enhance>Convert to Black and White” option. It’s called Scenic Landscape and converts the green to being a darker value than the red.

This setting is “Vivid Landscape” but I have a reall problem with the way it converts the red to being so much of a lighter value than the green. That's just not right.

One of my favorite settings to use is Infrared. It makes the darks as dark as possible and the lights as light as possible and you get to focus on the medium values.

Another way to get a black and white conversion is to use “Image>Mode>Grayscale”. I think this setting actually gave me the best comparative value of all the fabrics.
Confused? That wasn’t my goal. What I wanted to do is to tell you not to blindly rely on what your computer does to your photo. If it doesn’t seem right it probably isn’t! Try again with different settings. Test your software with photos of fabric that you feel you “know” and then find the setting in your software that gives you the right results. Then you will be more confident relying on the software when you have more difficult value puzzles to solve.