- Versatile black and white
- Grayscale and Line Art
- RGB images
- Convert to Grayscale
- Desaturation (remove colors)
- Grayscale vs Desaturation and Other Transformation Techniques
- Print grayscale images as black and white halftones
Versatile black and white
In photography, black and white photos are actually shades of gray. In digital imaging, these black and white images are called grayscale to distinguish them from black and white lines.
Grayscale and Line Art
Grayscale images store values for brightness levels, not color information. A typical grayscale image has 256 shades of gray, ranging from 0 (black) to 255 (white).
Black and white line art is usually two-tone (usually black and white) images, pen drawings, or pencil sketches. Converting a photo to line art (as shown in the image) can be done for special effects, but with only black or white pixels, photo details will be lost.
When converting a color photo to black and white, the image is grayscale.
While it’s possible to scan a grayscale image in color or take a digital black-and-white photo (with some cameras), skipping the color step, in most cases the images we work with start in color.
Color scans and photos from digital cameras are usually in RGB format. If not, it’s usually common to convert to RGB and work with the image (edit in a graphics program) in that format. RGB images store the red, green, and blue values that typically make up a color image. Each color is made up of different amounts of red, green and blue.
Sometimes it is necessary or desirable to print or display black and white (grayscale) photos. If the original image is in color, you can use graphics software such as Adobe Photoshop or Corel Photo-Paint to convert the color image to black and white.
There are several ways to turn a color photo into a black and white photo. Each has its own pros, cons and best uses. Trial and error is usually the best approach. The most common methods use the “convert to grayscale” or “desaturate” (or “remove color”) option in image editing software.
Convert to Grayscale
One of the easiest and often most effective ways to extract color from 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 colors are replaced with grayscale. The image is no longer in RGB.
Inkjet printers love RGB, so you can sometimes get better print results if you convert an image to RGB after going to grayscale – it’s still grayscale.
Corel Photo Paint: Image † Convert to… † shades of grey (8 bit)
Adobe Photoshop: Image † Mode † shades of grey †
Adobe Photoshop Elements: Image † Mode † shades of grey (reply Okay to the question “Cancel color information?”)
Corel Paint Shop Pro: colors † grayscale
Desaturation (remove colors)
Another option for the transition from color to grayscale is desaturation. Some image editing programs have a desaturation option. Others call it color drop or require you to use the saturation controls to achieve this effect.
If an image’s RGB values are desaturated (color removed), the values of each are the same or nearly the same for each color, resulting in a neutral shade of gray.
When desaturated, shades of red, green and blue become gray. The image is still in the RGB color space, but the colors become gray. Although undersaturation results in an image that appears gray, this is not the case.
Corel Photo Paint: image † to coordinate † discolor
Adobe Photoshop: image † to coordinate † discolor
Adobe Photoshop Elements: Improve † adjust color † Remove color †
Corel Paint Shop Pro: Hue saturation † Set “Brightness” to “0” † Set “Saturation” to “-100” †
Grayscale vs Desaturation and Other Transformation Techniques
Theoretically, a single color image converted to grayscale and desaturated to grayscale is equivalent. In practice, subtle differences can come to light. A desaturated image may be slightly darker and may lose some detail compared to the same image in true grayscale.
This may vary by photo and some differences will not be visible until the image is printed. Trial and error may be the best method to use.
Some other methods of creating a grayscale image from a color image include:
Convert to LAB mode and extract only the luma channel for your black and white. The result is very similar to grayscale mode.
Extract one of the RGB or CMYK channels by using one or by combining several channels to get the effect you want.
Instead of removing all colors evenly with desaturation, use the Hue/Saturation settings to reduce each channel individually for custom effects.
Create a monotone (with a color other than black) or a duotone for an off-color, off-black and white effect.
Print grayscale images as black and white halftones
Printing with black ink converts a grayscale image into a black dot pattern that mimics the solid tones of the original image. Lighter grays consist of fewer or fewer black dots that are far apart. Darker grays contain more or more black dots with less spacing.
So when you print a grayscale image with black ink, you are essentially printing a black and white photo because the halftones are just black dots of ink.
You can create digital halftones directly from the software to the printer. The halftone effect to be used can be specified in your PPD (PostScript Printer Driver) printers or specifically set in your program.
When printing black and white photos on an inkjet printer, you can vary the results by printing in black ink only or by having the printer use color ink to print grayscale. Color shifts can occur when using color inks, ranging from subtle to obvious. However, black ink alone can lose some fine detail and result in more visible ink dots – a more noticeable halftone.
For commercial printing, leave grayscale images in grayscale mode unless your service provider advises otherwise. Depending on how you print, black and white halftone screens are much smoother than what some desktop printers can do. However, you can specify your own screens in your software (or create special effects) if you wish.