I am photographing given points along an artificial stream bed and want to document algae growth over time. There may be up to 7 different shades of green (algea) in a given photograph. Can Photoshop produce an accurate pixel count of each shade? I would really appreciate a step by step solution if you know of one. The magic wand tool does not appear to very reliable for this quest.
You could use select color range with Fuzziness set to zero to sample the color you want to count. The use the Histogram Panel to get a count. Mouse over the Histogram to get the count at a specific level. You may want to limit the Channel to which ever one works best ie the green channel.