B&W (Grayscale) Conversion in GIMP

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.

The views and opinions expressed in this article are those of the author and do not necessarily reflect the views and opinions held by dpreview.com or any affiliated companies.

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Total comments: 2
john Clinch
By john Clinch (Feb 9, 2013)

Thanks I really enjoyed that.

I certainly hadn't seen Value. Lightness and Luminosity defined before

I do have GIMP installed but my methods seem to be work better with 16 bit images or in the RAW converter. So i seem to do almost everything in Lightroom now. Lightroom has a limited tool pallet for this work but I've enjoyed learning to work with it. But it looks like I need to give GIMP another look.....

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patdavid
By patdavid (Feb 12, 2013)

You're welcome, I hope it was helpful!

Yes, 16-bit has advantages when editing images for sure. There is preliminary 16-bit support in recent builds of GIMP (not stable), but to be honest, the overall techniques and ideas are certainly transferable to other software.

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Total comments: 2