What is spot colour?
Basically Spot colour refers to a black and white photograph with an area of colour.
The area of colour can be created by various means. You can add colour to a black and white photo, or you can remove colour from a coloured photo. Adding colour is often referred to as tinting. Removing colour is called a monochrome conversion. In both instances you want to apply the effect to only selected parts of the image, resulting in both black and white and coloured parts to the picture. Masking is the process of preventing an effect from changing selected parts of the image, as if you were using masking tape. Masking can be done to protect either a designated area or a designated colour.
Tinting was often used to produce colour portraits at a time when photography was predominantly monochrome. The images have an old world charm. It doesn’t however look like a colour photograph. Somehow it fails to achieve it’s objective. The lips and cheeks are two rosy, the skies are not authentic and blocks of colour like vegetation or hair or skin lack variation in hue. Overall they look unconvincing.
Andy Warhol used the technique in his famous Marilyn Munroe silk screen prints. The colour never looked natural, but created a gaudy poster like effect. Perhaps the defining characteristic of the Pop art movement.
In the instance of spot colour the tint need only apply to the object or area of interest. A contemporary example is from the movie Sin City. The opening sequence of this movie is shot in black and white except the red dress of the girl. The red looks to have been added by tinting.
2. Area of interest is masked
Alternatively a colour photograph can be desaturated leaving just a small area of remaining colour. This is often used to draw attention to the subject (coloured) and lead away from distracting elements (monochrome). For instance you might photograph a crowd, convert the image to monochrome, with just one person in colour. Alternatively the coloured area could be a flower, a woman in a red dress, a telephone box, a tree in a city, the eyes or lips of a face.
Some have criticized this approach as lazy photography. The argument being that a well composed photograph does not need this augmentation. I disagree. At the end of the day it is just another tool for creativity. It is similar to cropping or vignetting or other editing tools to focus attention on the subject. It can be predictable and boring, however it can also be creative and striking. My tip, don’t use it all the time. Pick and choose interesting and unexpected elements to highlight. Don’t conform to conventions. Make the image pop.
Another piece of advice. Often the colour masking needs to adhere to the outline of the chosen subject. The mask needs to be sharp and match well the outlines of the object. Smudging of the borders generally does not look good.
3. Colour of interest is masked
A third technique is to desaturate all but one of the colours in an image. This approach differs to the former approach in that you can tie together different areas within the photograph by virtue of a common colour. The effect can be hypnotic in a well chosen image.
It works well when there are themes emerging in the picture. For instance a yellow honeybee departing after collecting nectar from the yellow anthers at the centre of a flower.
Some cameras and phone cameras have this option for selecting a colour for spot colour on their shooting menus. It is worth having a look through the menus.
In gimp (and Photoshop) the process is simple. You duplicate the photo into two layers. The top layer is converted to monochrome. The bottom layer remains coloured. You then apply a mask to the top layer to reveal areas of the bottom layer. As Mark Pedlar puts it, you punch a hole through the top layer.
In Lightroom you apply a monochrome transformation then mask that transformation in the selected areas. As if you were rubbing paint off of certain areas of a painting. It is similar but different to the Photoshop approach.
At the heart there is a philosophical difference between these two programs. Photoshop will permanently change the pixels in the images, whereas Lightroom seeks to apply lossless transformations that can be undone at any stage, leaving the original pixels unaltered.
The area for masking is created using selection tools. Most people are familiar with geometric shape selection (rectangle and ellipse) and the paint brush tool. Modern software often contains a wealth of smart selection tools like the magic wand, the lasso tool, the magnetic lasso (magic scissors in Gimp) , rapid select, colour select and so on. The final selection however will conform to three basic shapes. The basic selection types are, soft edged , sharp edged and luminance based selections.
First have a look at this image:
In this exercise imagine the black and white layer is sitting over the top of the colour layer and we are going to cut a hole in the black and white layer. The resultant sandwich will vary depending upon the shape of the hole. Firstly we will make a fluffy soft edged hole like what you would get using a broad blurry paint brush tool.
Not too bad but you can see there is a green fringe around the subject. You can try painting this away by switching the selection tool to the “remove selection” mode. I find however that it often proves hard to remove unless you make the paint brush a lot smaller and crisper. It is also quite time consuming.
This time we will cut the hole sharply to fit the subject exactly. I did this with the rapid select tool (or the magic scissors tool). The computer looks for lines of high contrast in the areas that I direct it to.
Most of the fringe has gone. It is a little tricky however around soft and fine features like the hair.
Lastly we will select the red colours in the face and jumper with the colour select tool. Do not use the magic wand as this will create a sharp selection like above. The colour select mode (in the select menu) will create a luminance based selection.
Here you can see we have achieved the colour select approach. The mask this time is a luminance mask, being derived from the red values in the original image. This type of mask has no smudging at all, but is limited to the colour that you selected .
As the background is fairly uniform in colour, we can try an inverted green mask to create a luminance mask that will approximate the effect of the sharp edged mask.
Overall that’s not too bad, but we have lost colour in the jeans and shoes as they contain tones similar to the colour we used in the mask.
My conclusion is that the sharp selection works best for this image. It may look daunting. Carefully tracing around a complex subject looks to be too hard to be practical. In truth with the rapid select tool it took me less than 2 minutes to make this mask. I suspect this is the preferred option to get a good spot colour image.
How to do Tinting
Tinting does not require the colour layer. We start with the black and white layer and use the colorize command. In photoshop this is found in the HSL dialog box. This is what we get. Of course you can pick whatever colour you fancy.
In Lightroom or Camera Raw you can achieve the same effect with the “split tone” filter. This filter however is more powerful and allows you the flexibility to allocate different colours to each of the light, medium and dark tones.
If we use one of the masks that we have already created, we can limit the colour within the image.
Now that is spot colour, but it is more poster like. Closer to the Pop art of Andy Warhol. You can of course create several different tints on differing layers and mix them with masking to get a more complex result.
Another way to create an Andy Warhol effect is to use the paint brush to paint colour onto the black and white image. A bit like the pen and wash effects. In photoshop I create a blank layer over the top of the black and white layer. In the merge commands I switch it from “normal” to “colour”. (You can also try “soft light” or “multiply”) Now you can paint away and create an Andy Warhol masterpiece. Combing the delicate tonal values of the photograph with the poster like brash colours of the paint brush.
Well that’s about it. We have covered the concept of spot colour. Also we have discussed different sorts of masking. And we have demonstrated tinting of a monochrome image. Have fun experimenting with these techniques.