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In the previous section we used the Color Channel to convert a color image to black & white. This section explores several other alternative techniques.
Grayscale. Choose Image > Mode > Grayscale. This converts the image from 3-channel RGB colors to a 1-channel grayscale image.
Desaturate. Add a Hue/Saturation adjustment layer and set Saturation to -100.
Gradient map. Add a Gradient Map adjustment layer and choose a B&W gradient.
Color blend. Add a new layer above image. Fill with black and choose color blend.
Color blend + correction. Add a new layer above image. Fill with black and choose color blend. Then add a Selective Color adjustment layer between black fill and image for correction.
The following illustration compares these methods.
Click on the Color button and squint your eyes. Which color appears the brightest? Most people's eyes are more sensitive to green. Converting to grayscale takes this into account and corresponds closely to the Luminance channel in Lab mode. Desaturate fails to emphasize green. Gradient map and color blend are better, but have too much contrast. A color blend with a Selective Color adjustment layer for correction comes close to a standard grayscale conversion. We will use this technique to simulate visual response to colors in the Black & White Filter.