The Many Faces of Black & White

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Grayscale vs. Line Art

B/W Grayscale vs B/W Line Art
Black and White Photos are really many shades of gray. Images by Jacci Howard Bear

In photography, Black & White photographs are actually shades of gray. In digital imaging these B&W images are called grayscale to differentiate them from black and white line art.

Grayscale images store values for levels of brightness as opposed to color information. A typical grayscale image is 256 shades of gray ranging from 0 (black) to 255 (white).

Black & White Line Art is typically 2-color (usually black and white) clip art, pen and ink drawings, or pencil sketches. Converting a photograph to line art (as seen in the illustration) may be done for special effects but with only black or white pixels, the details of photographs are lost.

When converting a color photo to B&W, a grayscale image is the goal.

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RGB Images

Color photographs are usually in RGB format
RGB is the typical format for digital photographs. Image by Jacci Howard Bear

Although it is possible to scan a color image in grayscale or take a B&W digital photograph (with some cameras) thus skipping the color stage, most of the time images we work with start in color.

Color scans and digital camera photographs are typically in RGB format. If not, it is often customary to convert to RGB and work with the image (editing in a graphics software program) in that format. RGB images store values of red, green, and blue that would normally make up a color image. Each color is made up of varying amounts of red, green, and blue.

Sometimes it is necessary or desirable to print or display Black & White (grayscale) photographs. If the original image is in color, a graphics software program such as Adobe Photoshop or Corel Photo-Paint can be used to convert the color image to some form of black & white.

There are a number of methods available for getting a B&W photograph from a color photo.Each has it's own pros and cons and best uses. Trial and error is generally the best approach.The most widely used methods are using the "convert to grayscale" option or the "desaturation" (or "remove color") option in the image editing software.

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Convert to Grayscale

Convert to Grayscale
Convert to Grayscale Then Back to RGB. Image by Jacci Howard Bear

One of the simplest and often most effective ways to get the color out of a color photo is to convert it to Grayscale -- a common option in image editing software. When converting an RGB color image to grayscale all the color is replaced with shades of gray. The image is no longer in RGB.

Inkjet printers like RGB so you can sometimes achieve better print results if you convert the image back to RGB after going grayscale - it will still be shades of gray.

Corel Photo-Paint: Image > Convert to... > Grayscale (8-bit)
Adobe Photoshop: Image > Mode > Grayscale
Adobe Photoshop Elements: Image > Mode > Grayscale (say OK when asked "Discard Color Information?")
Jasc Paint Shop Pro: Colors > Grey Scale

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Desaturation (Remove Colors)

Desaturation looks a lot like grayscale
Desaturation looks a lot like grayscale. Image by Jacci Howard Bear

Another option for going from color to shades of gray is desaturation. In some image editing programs there is a desaturation option. Others call it color removal or require that you use the saturation controls to achieve this effect.

If the RGB values of an image are desaturated (color removed) the values of each are the same or nearly the same for each color, resulting in a neutral gray shade.

Desaturation pushes the Red, Green, and Blue hues towards gray. The image is still in the RGB colorspace but the colors turn gray.While desaturation results in an image that appears to be grayscale, it's not.

Corel Photo-Paint: Image > Adjust > Desaturate
Adobe Photoshop: Image > Adjust > Desaturate
Adobe Photoshop Elements: Enhance > Adjust Color > Remove Color
Jasc Paint Shop Pro: Hue/Saturation > Set Lightness to "0" > Set Saturation to "-100"

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Grayscale vs. Desaturation and Other Conversion Methods

Grayscale vs. Desaturation
Grayscale vs. Desaturation - sometimes differences can be seen. Image by Jacci Howard Bear

In theory, the same color image converted to grayscale and desaturated to shades of gray would be equivalent. In practice, subtle differences may be apparent. A desaturated image may be slightly darker and can lose some detail compared to the same image in true grayscale.

It can vary from one photo to the next and some differences may not be obvious until the image is printed. Trial and error may be the best method to employ.

Some other methods of creating a grayscale image from a color image include:

  • Convert to LAB mode and extract only the Luminance channel for your black & white. The result is pretty much like grayscale mode.
  • Extract one of the RGB or CMYK channels, using one or combining a couple of channels to get the effect you want.
  • Instead of removing all the color evenly with desaturation, use the Hue/Saturation controls to desaturate each channel individually for custom effects.
  • Create a monotone (with a color other than black) or a duotone for a not-quite color, not-quite black and white effect.

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Print Grayscale Images as Black and White Halftones

Grayscale images become b/w halftones
Grayscale Images Become B/W Halftones.

When printed with black ink, a grayscale image converts to a pattern of black dots that simulates the continuous tones of the original image. Lighter shades of gray consist of fewer or smaller black dots spaced far apart. Darker shades of gray contain more or larger black dots with closer spacing.

So, when printing a grayscale image with black ink you really are printing a B&W photograph because the halftone is simply black dots of ink.

You can produce digital halftones direct from the software to the printer. The halftone effect used may be specified in your printers PPD (PostScript Printer Driver) or set specifically in your software program.

When printing B&W photos to an inkjet printer, results can be varied by printing with black ink only or allowing the printer to use color inks to print the shades of gray. Color shifts -- from negligible to obvious -- may occur when using color inks. However, black ink only can lose some of the finer details and result in more obvious dots of ink -- a more noticeable halftone.

For commercial printing, leave grayscale images in grayscale mode unless your service provider suggests otherwise. Depending on the printing method, the black and white halftone screens are much smoother than what some desktop printers can acheive. However, you can specify your own screens in your software if you prefer (or to create special effects).

See "The basics of color and black & white halftones" for more on working with halftones.