Digital Techniques - The Colours of Black & White Part II

Well hopefully I raised some interest in the previous posting as to getting more from digital black & white images.

Now we'll move onto some specifics of the conversion process...


Well I 'blithered' on for long enough about shades of grey and all that horrible mathematic stuff in the last posting. Let's get onto the conversion.

The following image shows the orignal image from the last posting along with several common black and white conversion techniques. I've included the histogram for the Red, Green and Blue channels as well as the Grey and Lightness values plus the number of colours you're left with.



The original colour image contained 154,774 colours, (much less than the possible 16,777,216 colours we have a maximum of.) Your original could obviously contain more or less colours depending on the subject. From the histogram you can see a nice spread of Red, Green and Blue as well as the Greyscale and Lightness values.

When we convert to black & white using 'greyscale' we get exactly that and only 256 colours. If you use the 'desaturate' we now only have 253 colours! I don't know why that happened, (Paintshop v.8), but look at that big spike on the graph, something went wrong. The next conversion is the 'channel mixer' option. I used a standard 30,60,10 conversion, (to mimic the human eyes spectral response), so it's pretty much the same as the greyscale conversion. The only handy thing about using the 'channel mixer' option is that you can alter the amount of Red, Green and Blue from the original mimicking the effect of using coloured filters for black & white film images. Still only 256 colours though.

Then we get to the conversion I came up with whilst playing around in Paintshop - All 2,175 of them! That's eight and a half times as many greys!

The final image, (from the first post), contains 3,427 colours.



Depending on your original image the colour shift amounts, curves etc. you can get thousands of shades - Very handy!

Onto the conversion:

If you've paintshop, photoshop etc. and have a good understanding of using layers then this is going to be a breeze. If you don't, well I'm afraid I'm not going to teach you as it'll take way too long for one small blog. Read the help files or check some tutorials online or even just experiment with your software package.

Make sure that you've got your image loaded and either perform a copy and paste or duplicate the image, (so that you don't alter the original - always a good idea!)

Now add a channel mixer layer to that image.
Layer(s) --> New Adjustment Layer --> Channel Mixer

Use a standard Red=30, Green=60, Blue=10 for now and make sure you check the monochrome box.

Now add a Colour Balance layer, I usually start with the values 5,0,-5 for the shadows and 3,0,-3 for the highlights. You can adjust these later but remember to make subtle changes to these - you'll only regret it later when you come to using curves!
You can however make larger changes to the midtones later to give a colour change such as sepis, (20,5,-20 is a good start for a subtle sepia.)

Right, that was fairly easy wasn't it? But we've still only got 256 maximum colours for now.

Now either copy or duplicate the original, (background), and make sure it sits above the layers you've already created.

Now change this new copy layers property to 'Luminance' for Paintshop or 'Luminosity' for Photoshop.

You should now have from top to bottom:

Copy Image - Luminosity or Luminance
Colour Balance - Adjustment Layer
Channel Mixer - Adjustment Layer
Original Image Background Layer

Doesn't look any different does it? (Some of you may have noticed a slight change in luminance.)

However if you now flatten this image, (or use 'copy merged') and make sure you wither save this new image or paste it as a new image. This final image now has a lot more than 256 greys available to it!

Well how has that helped?

On the original layers work you can adjust the image filtration through the channel mixer, (red filter, yellow filter etc. or do as I do and adjust to suit.)
You can also adjust the colour layers to alter the 'coolness', 'warmth', or 'neutrality' of the image.

The 'Luminance' or 'Luminosity' layer is the real masterpiece here - it's what gives us all our colours or shades of greys. Instead of copying the original image in that layer you could even try a HDR or tonemapped image and adjust the opacity to suit. Or maybe adjust it's curves layer or brightness or blur it a little - You'll start to see what you can do with the image now, a heck of a lot more than you could with only 256 shades that's for sure!

Even if you slatten the image and start doing some more post processing afterwards as you've got an extended range of greys you can do a whole lot more. If you start seeing funny bands of colour or colour 'fringes' you probably overdid it at the shadow/higlight layer part, (I did warn you!), so adjust the original layer work.

If this is not so straight forward looking have an experiment with the images you've produced. You'll soon start to see the adantages over the other conversion methods.

Here's some other images that I've produced using this method:

9,669 colours




1,543 colours, layered with a HDR copy on the Luminosity channel




4,088 colours, layered with a HDR copy on the Luminosity channel



Now you can see how you can get much more from your digital black & white images and why I'm finally quite happy with digital. The great thing is that these print great from a standard High Street or local photo processor on their colour systems.
If any of this doesn't appear quite straight dorward then have an experiment after all it's how I came about this in the first place.

Welcome to he world of extended digital black & white.