To create a black-and-white image, use the Threshold command. Select the threshold lightness value—below which all pixels are changed to black and above which all pixels are changed to white. This command does not change the color depth of the image.
Note:The Threshold command creates an image with pixels of two colors: black or white. To create a “black-and-white” photograph, which is really made up of many shades of grey, see Creating Greyscale Images. You can also decrease an image’s color depth to 2 colors, which gives you options for how colors are reduced that may result in more natural-looking images than the Threshold command. For more information, see Decreasing Color Depth to 2 Colors (1-bit).
Important: To apply this command to a selection, the image must be a 16 million (24-bit) color image (otherwise the command is applied to the entire image). In addition, adjustment layers are available for 16 million (24-bit) color or greyscale images only. To increase the color depth of an image, see Increasing the Color Depth of an Image.
To use the Threshold command:
To limit the correction to a specific area, make a selection in the image. See Using the Selection Tools.
Do one of the following:
To modify the image pixels directly, choose Adjust > Brightness and Contrast > Threshold.
To create an adjustment layer, choose Layers > New Adjustment Layer > Threshold. For information on adjustment layers, see Using Adjustment Layers.
Click the Zoom out button until you can see the entire image in the preview windows.
In the Threshold edit box, select a pixel lightness value that determines which pixels change to white (those above the threshold) and which pixels change to black (those below the threshold). The value ranges from 1 to 255. Adjust the threshold until the image in the preview window is satisfactory.
Click OK.
Reducing the Number of Lightness Levels