In the Channels' Palette, take a look at all the channels and see which one has the most information. Make a note of the best channel. You will need this information later on.
Next, in the Layers' Palette, click the New Fill Button at the bottom of the palette (Figure 3) and choose Channel Mixer. In the dialog box select Monochrome. The Red Source Channel will be at 100. Now, take the channel that had the best tonal information and move the slider so that it has the highest number. You will need to move the other sliders and work with the image till you get the best overall improvement in your image and the numbers add up to 100. (Figure 4) Click OK.
Next, click the Snapshot icon on the bottom of the History Palette. Rename your layer Grayscale. Or right click the last layer (Channel Mixer layer) of the History Palette and select Merged Layers from the pop up menu, click OK. This saves the grayscale image for later. (Figures 5, 6 & 7)