Note: The screen shots in this lesson are taken from Photoshop CS, but where differences exist between this full version of Photoshop and Photoshop Elements, a note will appear in the text.

The sample file used with this lesson (show below) can be found here. To download it, open it in a new browser window using this link, then use right-click Save Image As...

Convert to Grayscale

This is one of the simplest methods for converting color images to black and white but often felt to be one of the least effective. However, it can work well in some circumstances so we are including it here.

All you need to do is open your image and select the Image -> Mode -> Grayscale menu entry. You may be prompted to discard all color information. You must click OK.

For this image the grayscale conversion is quite acceptable. We will compare this image with those obtained using the other methods later.

The single channel black and white saved image is now also approximately 3 times smaller than the equivalent three channel color image, but you will not be able to convert this image back to color as all the color information has been discarded. For this reason, it is always a good idea to keep the original image.

To do any color work on this image after the conversion, such as in adding color tone for monotone printing for example, you will nee to convert the image back to RGB mode first by selecting Image -> Mode -> RGB.

Desaturate the Colors

With the color image window select, click the menu entry Image -> Adjustments -> Desaturate. The result is shown below.

This operation has the effect of making all the colors look tonally very similar. Looking at the desaturated image we can see that there is less difference between the pink of the lips and the surrounding skin than with the grayscale conversion. You can see this effect using the Channels palette - Red, Green and Blue channels look much the same. In some images that contain red and yellow for example, desaturation can make them tonally indistinguishable as both RGB colors (255,255,0) and (255,0,0) both desaturate to (127,127,127).

This conversion method saves having to change the image back to RGB mode to carry out some RGB-only adjustments.

Note: The desaturate conversion results in a standard grayscale conversion using a Channel mix of 30% Red, 60% Green and 10% Blue.

Use Lab Color Mode

Note: Photoshop Elements does not include Lab Color mode so this conversion method is not possible with that version of Photoshop.

This method is slightly more complex, but is more popular than the previous methods as the results generally give better tones. With the color image open, click the Image -> Mode -> Lab Color menu entry.

Photoshop now displays the image in a different way. Looking at the Channels palette, in place of the Red, Green and Blue channels, you will see a Lightness and two (a and b) color channels. You must now right click on the a channel and select Delete Channel and then repeat for the b channel. You are now left with only the channel containing only the lightness information from the image. Convert the image to Grayscale using Image -> Mode -> Grayscale. (You can then convert back to RGB mode using Image -> Mode -> RGB if you want to make any RGB-only adjustments.

The image converted in this way generally separates colors better so you can still see differences between colors better and has lighter tones which some people prefer. The conversion process on our sample image is shown below.

Use Channel Mixer Adjustment Layer

This method is very flexible as it allows you to mix together the contributions of the Red, Green and Blue color channels in any combination to get the black and black and white image you would like. Also, as it uses the Channel Mixer as an adjustment layer, you are leaving the color information in the image untouched.

Open the image and the Layers palette. Create a new Adjustment Layer by clicking on the half black/white circle icon. The following menu will be displayed. Select Channel Mixer...

The Channel Mixer dialog will be displayed.

By default, Photoshop sets the Re channel to 100% with Green abd Blue at 0%. As a general rule the combined sum of the channels should be equal to 100% or as close as it can be. This has the effect of keeping the image brightness at roughly the same level. This rule is made to be broken and we will do that shortly.

First, ensure the Monochrome box is checked. Now you can adjust the percentage of Red, Green and Blue channels to model the effect of those filter colors on black and white.

Red channel at +84% and Green channel at +16% creates a similar effect to a red filter on the camera with black and white film.

The image below was generated with 50% Red and 50% Green simulating a yellow filter.

The second image below was generated with 84% Red and 16% Green. This gives us a slightly lighter overall image.

The final image generated using the Channel mixer breaks the rule that the sum of all channels should equal 100%. The settings here work well to get dark and moody landscapes, but can work well with other image types such as this one. Set the Red channel to +60%, the Green channel to +72%and the Blue channel to -34% (minus). Set the Constant slider to -2%. The constant slider controls the overall brightness with a positive value making the image lighter.

Note: It is often useful to look at each of the individual channel contributions for the most pleasing ones so that you can start your combinations with those. To do this, select the individual channels from the Channels palette. Play with the amount of channel contributions to get the effect you want. The best result will be different from image to image.

Use Calculations

This last conversion method is good for creating black and white images with high contrast that emphasize texture (particularly useful for enhancing skin texture).

Open the image and click the Image -> Calculations... menu entry.

The Image Calculations dialog will be displayed.

Ensure the Preview option is checked and move your dialog to the left or right so you can see the effect of your changes on the image. Select Source 1 to be the Red channel. Select Source 2 to be the Green channel. Set the Blending type to be Overlay with an Opacity of 30%. Select the Result to be a New Document to create a new window containing the black and white image.

Side-by-Side Comparisons

Original Color Image	Convert to Greyscale
Color Desaturation	Lab Color Lightness
Channel Mixer (Red/Green/Blue +50%/+50%/0%)	Channel Mixer (Red/Green/Blue +84%/+16%/0%)
Channel Mixer (Red/Green/Blue +60%/+72%/-34%)	Image Calculations Src 1: Red, Src 2: Green, Overlay, 30%