Many cameras have filters built-in. My Leica D-Lux6 has a filter called “One Point Color”, which essentially allows the user to select a colour to retain, and transforms the remainder of the image into a monochromatic picture. This is sometimes called the colour-splash effect. Here is an example of the filter at work. The photo was taken at the Brickworks in Toronto. You can see I have selected a point from the red chairs to act as the “one point color”. You can see it has highlighted the chairs nicely, but also some of the bricks, as they contain some red hues.
This is not unusual, as these filters are not perfect. They attempt to almost “isolate” an object of interest by selecting all objects that are within the RGB range of the red point selected. So selecting a point likely selects a small neighbourhood, and uses the range of colours in that neighbourhood to specify a colour. Consider a second image which contains pink flowers which are the colour objets to be retained.
Now let’s look at the “One Point Color” filter, picking a “point” in the central flower selects pink regions throughout the photograph. The results are interesting, but don’t seem to really represent the original colours of the flowers.
The colours almost seem muted. Below is a comparison of the processed (left) versus the original flower colour). The other problem with these filters is that they take time to activate and aren’t always true-to-form. The colour-splash effect works best with large, closely connected objects with a fairly uniform hue.