Black and White Photography, Part 3

In this entry, I’ll look at a conversion technique that gives more control over the techniques in the last post.  But this isn’t yet the cream of the crop – this doesn’t have the ability to give the fine control offered by the techniques I’ll cover in the next post offer.  But still, the technique I’ll cover today does have its place in photo editing.

Technique 5 – Gradient Maps

This technique gives a fairly nice conversion, although making adjustments to it does take a little bit of work.  However, it doesn’t require the time consuming effort of the dodge and burn layer.

Create a gradient map adjustment layer above your image.  If your colours are set to the default of black foreground and white background, then you will get a gradient that colours the image a black in the darkest areas, gradually fading through grey until you get white in the highlights.

Setting this layer to a blend mode of colour gives exactly the same results as the solid colour adjustment layer does, because it is doing the same thing – using a layer without colour to remove the colour from a colour image.  But if we leave the gradient map layer’s blend mode on normal, we can do something different.

The gradient map adjustment layer takes the brightness of a colour pixel and uses that to place it within the gradient.  It then takes the colour from that part of the gradient and makes the pixel that colour.  For example, if a pixel’s colour has a brightness of 50%, then it will take the colour that is halfway along the gradient and change the pixel to that colour.  And if the original pixel had a brightness of 75%, then it will take the colour that is three quarters along the gradient and change the pixel to that.

However, the basic gradient that comes from a black to white only plots a pixel to a black and white pixel which is the same brightness that it started as.  But this can be changed.  If we open up the gradient editor (double click the adjustment layer icon, then click on the gradient that appears in the dialogue box), we can add additional shades of grey to fine tune the black and white conversion.  You can see that there are little tabs (called colour stops) underneath the gradient.  We can add more of those to control how the image is converted to a shade of grey.

Click underneath the gradient editor, and you will add another colour stop (by default it will be black).  Drag it to roughly the middle of the gradient.  You’ll see that the image is darker than it was; this is because the gradient map adjustment layer is now taking all the pixels that have a brightness of 50% (because the colour stop is halfway along) and changing them to be black pixels.  This looks a little drastic, but we can change the stop’s colour by clicking on it and then clicking on the colour box below it to change it.  If we make it a shade of grey with a brightness value of 33%, then the gradient map will take any colour pixels with a brightness value of 50% and remap them to a grey pixel with a brightness value of 33%.

Using this same method, we can add colour stops all along the gradient if we wish, allowing us to control exactly how the image is converted into black and white by remapping pixels based on their brightness.  However, this method still has disadvantages.  We are not able to use this method to increase or decrease the brightness of pixels based on their colour, only brightness.  However, this technique is not without its use.  It can be used to add colour toning to an image after we have converted it to black and white by choosing colours instead of shades of grey in the gradient map.  I’ll revisit this technique in a later post to show how such toning can be done.


The next techniques do give us the ability to adjust the image based on colour, but at the expense of complexity.  We’ll look at them in the next post.