change color original

You may want to change the color of an object or set of objects in a scene. Darktable provides several ways to achieve this effect, so let's take a look at a few different ways to turn the above car from orange to green.

Color Balance

color balance

This method is preferred since it uses a scene-referred workflow. The advantage of the color balance module is you can precisely adjust the hue of the color for the shadows, midtones, and highlights. However, as seen here I needed to use both a parametric mask (with the mask selecting both a specific hue and chroma) as well as a drawn mask to only apply to the orange car. This is more effort than other methods, but also gives more precise results.

Color Zones

color zones

The color zones module makes it easy to adjust a specific color by finding it on the line in the hue tab and dragging it up or down towards the desired color. This allowed me to easily alter the car's color. I did need to use a drawn mask (as seen in the screenshot) to only affect the car and not the other orange pixels elsewhere in the photo. While this module is intuitive and easy to use, I found that adjusting to a specific target hue was somewhat challenging.

Color Look Up Table

color look up table

For this particular image, the color look up table was not that fast or friendly. While I was able to change the color after selecting several patches (and even creating a custom patch) and adjusting their hues (and using parametric and drawn masks to only select the orange of the car), I found that I still had difficulty selecting some of the colors around the edges in order to adjust them. In situations where it is easy to completely select a color with a patch or two, this module works well and is fast, but in this case with the variations in hue it was more difficult and time-consuming than the other options.

Conclusion

There are multiple ways to achieve this effect that all work, but you should choose which one is the best fit for the particular image you are working on. The color zones and color look up table modules seem to work well when less precision is required (or there is less variation in the color you are trying to select) whereas color balance takes more time to use but allows you to deliver a more precise result.