Converting Color Images to B&W in Gimp

[jbeise]

Duplicate the original image (Ctrl+D) and right-click on the copy. Select Image -> Mode -> Grayscale. I don't know how this conversion works in GIMP, but I have read that Photoshop uses a standard mix of the RGB channels for their grayscale conversion: RED=30%, GREEN=59% and BLUE=11%. Supposedly this mix accounts for the eye's sensitivity to different colors. This formula does a pretty nice job in the general case, but some images do not work as well with it, particularly if the green channel component is not strong.

I suspect GIMP uses a similar formula. My experiments with the Channel Mixer support this.
if I use desaturate instead. Duplicate the original image (Ctrl+D) and right-click on the copy. Select Image -> Colors -> Desaturate. Unlike the grayscale mode change above, the channels are not remixed in different percentages, so we should expect different results.

A third method is to consider the red/green/blue channels of the image. Each one can be represented as an independent grayscale image. Right-click on the original image and select Image -> Mode -> Decompose. Select the RGB option and click OK.
Very often the green channel contains an excellent B&W version of the image. If nothing else, taking a look at the RGB decomposition is important to give you an idea of where the important information is in your image, and where the noise is.

[wulf]

If aiming for a monochrome result, I invariably decompose to RGB channels. That gives me three versions of the image which can be combined as I need. Often one is a good base image and then I apply translucent versions of the other channels (perhaps changing the mode to something like screen or overlay or using layer masks) to fine tune the effect.

Have you got any illustrations to go along with your suggested steps?

Wulf

[iffles]

jbeise - your tutorial seems to be copy/pasted in part from this article on gimpguru.com (a rather good one, actually).

Personally, I prefer using the channel mixer. You can see my tutorial on how I do this in gimp here.

[wulf]

Copying and pasting from other sites isn't good. Please contact us if you are the author of the original article or have your own text to replace it (and the same for the other tutorial published recently) otherwise we will remove them. Sharing ideas is great but it's got to be in your own words and not ripped from another site.

Wulf

ps. Jennifer - thanks for spotting this.