Boo's Digital Photography Tutorials.  No. 2

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Partially de-saturating colour images using layers ~ and other tips!

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Page updated July 2004.

This photograph has been de-saturated, but not completely, leaving some natural colour.    This is one of my personal favourite techniques for creating a monochrome image. It doesn't actually result in a black and white image, but the colour is largely removed, giving rise to an image that looks like a warmly coloured black and white photograph. It works best on images with good detail and texture and is especially effective on images where the subject lends itself to a black and white treatment, but then looks a little flat when the colour is removed. This technique boosts the tonal range of the colour image before desaturating and this gives much more detail and texture to images that otherwise fall flat when devoid of colour.

Why use layers?

There are of course, many ways of making a colour image black and white or other types of monochrome, including the use of combined de-saturation adjustment layers or an adjustment layer using the channel mixer, both techniques offer significant options for tonal manipulation, but are beyond the purpose of this particular tutorial in detail, although they're covered briefly lower down.

Part of a sculptured seat in the Grizedale Forest.  In this technique, you will add two layers to your image and then manipulate their transparency to get the desired result. Using layers to make image adjustments is incredibly flexible as if you don't like the effect, simply delete the layers and your original image remains untouched. Perhaps the most powerful reason for using layers to make adjustments to images is that you can vary the amount of transparency of each layer, infinitely adjusting the appearance of your image through transparency until you're happy with the results. You can also do this with sharpening, noise reduction, saturation, contrast etc.

Whilst I acknowledge that perhaps the most widely used image editor is Adobe's PhotoShop, I personally use Paint Shop Pro, but I believe the technique will work equally well in either application, so I'll avoid specifics in the instructions, consultation with your help files will show you how to access the functions I've described and named.

Right, let's start:

Open your colour image in your chosen editor and make any retouching adjustments you want and then duplicate the main image layer and make the blend mode 'soft light'. This really enhances the contrast, saturation etc. and probably at this point, the photograph will look pretty horrible and overly harsh. Then create a new layer on top of your original and soft light layers as an adjustment layer for Hue, Saturation and Lightness and put the saturation at -100%, so the image now appears black and white. By now fiddling with the transparency of both the soft light and the saturation adjustment layer above it (leave the original alone, at the bottom), you can get the increased texture and contrast and colour saturation you want.

I tend to put the HSL adjustment layer (the top one) transparency at about 80-90% (i.e. 10-20% transparent, just showing some of the colour from the bottom, picture layer) - I slide the opacity slider just to the point where there is a hint of colour showing but not too indentifyable - some colours may well appear before others (usually reds and greens), you simply adjust this transparency until you like the results. You also need to adjust the soft light layer (the middle of the three) until you like the tonal appearance - I find you get the most acceptable result somewhere between 50 and 70% opacity, 100% will almost certainly be too severe. Gradually adjust the transparency of the two layers until you like the results.

At the point where you're happy with the appearance, merge the layers and make any sharpness adjustments etc. and export the file as a new image, taking care not to over-write your original image file.

An example:

This first frame example shows the colour original, the second frame is the colour original turned to a simple grey scale (although this is not the best method of making an image black and white) and the third frame shows the finished result of using the technique outlined above; a warmer image with an extended tonal range.

The orginal colour image.  The colour image turned to a grey scale.  The colour image partially de-saturated using the above technique.

If you're feeling more adventurous:

There are many ways to remove the colour from an image, above I've described perhaps the simplest method using a layer, purely for ease and it works pretty well with this technique, but if you're more confident at image editing and using layers, there are perhaps even better ways of taking the colour out of the image. These days I would probably duplicate the colour image within my editing application and make one copy monochrome to my satisfaction, copy this as a new layer above the colour original, then make the blend with the colour image until some colour remained and add a tint layer above the new image and tweak the transparencies as desired.

 [In this image, the colours made the image very flat tonally, so it was stripped to individual colour channels.]  I have several favourite techniques for creating black and white images and the method used is largely determined by the image itself, some simply lend themselves more to one technique than another - knowing which, comes with experience and is largely down to personal preferences and taste. The two techniques I use most often are desaturating with HSL adjustment layers, or an adjustment layer using the channel mixer. For complex images tonally, I sometimes separate the channels, then blend them as separate layers with masks etc., but the image needs to be worth the investment of time, see the image of the lady above right, her clothes and the chair were the same colour when de-saturated, so it needed more attention.

 [This image was made monochrome initially using HSL layers.]  For the HSL layer technique, I add two HSL adjustment layers above the image and give the first one a blend mode of 'color' and in the topmost one, reduce the saturation to -100. Highlight the middle color layer and by tweaking the hue of the image it changes the tonal qualities of the monochrome result. This can be especially useful where there are very strong colours in the original image, but which look tonally similar when the colour is removed.

Adding an adjustment layer for the channel mixer can work well with an image that is tonally dominated by one colour, each channel can be adjusted to bring out tonal detail perhaps not obvious in colour. Check the monochrome box and then the three channels, one each for red, green and blue can be adjusted individually to taste, but the total amounts need to approximately add up to 100 e.g. red=21, green=61, blue=15. If they don't add up to around 100, the overall lightness or darkness will be effected, so this may prove to be a useful additional adjustment. Less than 100 will darken, a greater number will lighten your image.

In the examples below, you can see how the tonal quality of the image can be changed to acheive different results, depending on the method used and settings selected. You'll never use 'greyscale' again.

The colour original. Desaturated using HSL adjustment layers. Desaturated using the channel mixer to give a different tonal emphasis.

Variations on a theme; further tips:

Platform stuck in time.  There are several variations you can apply to this technique depending on the individual image. In some cases, the soft light blend mode of the duplicate layer is too extreme and heavy handed. Another technique for increasing local contrast that I like to use on more subtle images is to apply Unsharp Mask (USM) with a very large radius, to a small amount and with no threshold - my starting settings are radius 50, amount 20% and threshold 0 - adjust to taste. This boosts the contrast of the image in a more subtle manner, giving a perceived increase in sharpness of the detail. If this is done on a duplicate layer of the image, as previously described, the transparency can be adjusted to get a pleasing result.

If when adding the soft light layer described higher up, the image becomes too dark, or the dark areas in it too prominent, a second duplicate layer of the main image can be used, but make the blend mode of this layer to dodge. Fully opaque, this layer will make the image very overly bright and blown, but reduce the opacity to less than 10% and the lighter areas are extended - it works especially well when combined with the soft light layer. One darkens, one lightens and in combination, they extend the tonal range.

An image can also be enhanced tonally by using a duplicate layer of the main image and making the blend mode to 'overlay' and reducing the opacity to a fairly modest amount. This gives a smiliar result to the soft light layer technique, but with some images can give a more pelasing result, it might be worth trying if the soft light layer wasn't satisfactory.

I hope that they're not needed.  Some images with dominant areas of blues or greens may not give rise to the desired result when the saturation layer is made partially transparent. In such cases, after blending the layers, changing the overall colour cast/balance of the image to a warmer temperature may restore the effect you were hoping for, or in fact any other colour cast you desire. In the image on the right, rather more colour was left in the image, but the overall effect was colder than the subject suited, so the colour balance of the image as a whole was adjusted to a warmer tone in keeping with the image theme.

My own technique for adding a colour overlay or tint to images is to create an adjustment layer for Hue, Saturation and Lightness and check the option to colorize. Choose a colour that's appropriate, from the colour wheel and I usually set the saturation at 50. You can then adjust the transparency of that layer to get the desired amount of colour into the image. Again, the use of layers allow a very subtle level of control and adjustment.

If you found it useful . . .

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