3 Ways to Convert Images to Black and White on GIMP

GIMP provides multiple ways to convert images to black and white.

Each method provides different results and levels of flexibility. The following are the different ways and the differences between them that you can use to convert the images. Choosing one over the other simply depends on your preferences.

GIMP Black and White Conversion

Let’s start with the easiest option out of the bunch.

1. Enabling Grayscale Mode

The image will open in RGB mode by default, but changing the mode to grayscale will automatically change the image to black and white. Grayscale, as its name implies, does not allow you any additional control over the image since it directly affects the color scheme. Intensity and color channels cannot be modified either. A single layer setting is also not possible. Once enabled, it will apply to the entire image, including all layers.

To convert the image to black and white using grayscale, click on the Image > Mode and select Grayscale radio. 

This will convert the image to black and white instantly.

You will also be able to input and edit in grayscale after selecting grayscale. Simply select RGB from Image > Mode to make this change. You will reintroduce color without changing the image that had been turned grayscale.

2. Using Desaturation

As opposed to grayscale, with desaturation you can choose the intensity of the black and white image you need. If you prefer, you can choose not to turn the image completely black and white.

By selecting the layer you want to make black and white, you can convert the image to black and white using desaturation. You can also select multiple layers by pressing the CTRL key.

Saturation can be selected by clicking on the Color option in the menu bar.

Using the Scale option, you can change the intensity of the black and white shades.

With this tool, the saturation level can be saved as a preset, so it can be applied to additional images as well. In addition to that, there are other desaturation modes such as Luminance, Luma, Lightness, Average, and Value. By changing the brightness and color channels, you can further modify the black and white shade applied to the image. These modes can be accessed by opening Colors > Desaturate, then selecting it again.

The image will open a pop-up window where you can apply these modes.

Instead of relying on the tool to provide various grayscale modes, you can fine-tune the RGB channels manually to get the exact black and white you are looking for.

3. Adjusting Through Channel Mixer

The Channel Mixer option allows you to customize every aspect of the image. Red, green, and blue levels can be adjusted to get the exact black and white tone you want.

To change the colors to black and white using the channel mixer, open Colors > Components > Mono Mixer. This will turn the image to black and white and open a pop-up window to customize the RGB channels.

Mono mixer option on GIMP

It is now possible to adjust the tonal value of the black and white image by modifying the RGB channels. The RGB channels should add to 100% for the same brightness level. As an example, if you set the red to 31%, green to 58%, and blue to 11%, you will get the same black and white toned image as the grayscale option. You can prevent this issue by enabling the Preserve Luminosity toggle. Adjusting the RGB layers won't affect the brightness levels.

Below is a sample. Dimming the blue channel level will result in a darker sky. With this technique, you can change the channel colors to make certain things stand out.

This technique has the advantage of being flexible. It's about bringing out the perfect lines and layout in the images without adding more noise for me.

The End: Using GIMP to Convert Images Black and White

Although grayscale is great for turning images black and white, it lacks the control that intensity and channel options provide when it comes to tuning the image. If you zoom in, the black and white image has a bit more noise than the grayscale once the saturation levels are decreased. Using channel mixing, you can adjust the image accordingly. So you can darken the sky, make a bright object stand out, etc. You can also control individual colors.