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B&W (Grayscale) Conversion in GIMP

patdavid | Software Techniques | Published Feb 7, 2013

A (relatively) comprehensive look at various methods to convert an image to B&W grayscale in GIMP.

I've walked through just about every possible method of generating a B&W grayscale image in GIMP, and present them with some notes and thoughts on each process.

The topic is a rather large one, so I broke them up into 5 different sections to make it a little easier to digest all of the information.  There's a good chance that something in the overall tutorial might prove helpful to developing your own B&W workflow!

Getting Around in GIMP - B&W Conversion Part 1

Using the straight Desaturate command, and how each of the modes calculates the final pixel values.  This mainly looks at how

  • Lightness
  • Luminosity
  • Average

will affect your final pixel values and results.

Getting Around in GIMP - B&W Conversion Part 2

This part looks at a common method of converting to grayscale using the Channel Mixer, and the various ways that the different RGB channels effect the results.  This part also provides a table of some common B&W film emulation values to use in the Channel Mixer.

Getting Around in GIMP - B&W Conversion Part 3

Part 3 decomposes the color image into it's constituent color channels based on the different modes.  This sometimes yields interesting results that can be further used when constructing a final grayscale version of the image (Part 5).

In particular, the modes that are looked at are:

  • RGB - All
  • HSV/HSL - V(Value) and L(Lightness)
  • LAB - L
  • CMY - All
  • CMYK - K
  • YCbCr - Y(Luma)

 Each of these color modes are then examined for their usefulness in representing the final image.

Getting Around in GIMP - B&W Conversion Part 4 

Part 4 investigates some functionality exclusive to GIMP, and how to use layers to adjust the grayscale image right on the canvas.

The exclusive parts deal with using GEGL c2g (color 2 gray) to automatically adjust local contrast during value determination based on the brightness of the surrounding pixels.

This part also touches on using the Pseudogrey algorithm to produce an image with up to 1786 different shades (far more than the 256 shades of gray available in a "true" grey image).

Getting Around in GIMP - B&W Conversion Part 5 

 The final part of this tutorial looks at using everything that was covered in the previous portions, and how to blend the different results together using simple layer masks.  This gives a great amount of control over the various tones in your image to highlight or depress various features.