Once you have converted a picture to grayscale, or if you are starting out with a black-and-white photograph, using Photoshop there are many ways to adjust and increase tones and shades. Whether you desire an artistic effect or simply want to accentuate the timeless effect of black and white, the ability to choose the intensity of your black-and-white image is at your fingertips.
Open Adobe Photoshop and the image you want to work with, using the "File" then "Open" menu.
To convert the image to black and white, bring up the Image menu and select "Mode" then "Grayscale."
Adjust the intensity of the colour channels by selecting from the Image menu "Adjustments" then "Variations." In this menu you can add various shades to the image and adjust the lightness or darkness.
To create an artistic effect, adjust the brightness and contrast of your grayscale image. Select from the Image menu "Adjustments" then "Brightness/Contrast," and pull the adjustment bars far from the centre point.
To create a dramatic and unique effect, it is possible to adjust the colour curves yourself. Select from the Image menu "Adjustments" then "Curves," and add points along the current colour curve, warping the image highlights and intensity as you desire.
These steps also work well using a colour photograph. The "Variations" option is particularly effective, as you can change all of the colours in the image, ending up with something entirely different to what you started with.