There are many different reasons why you might want to change the color of your photos. Colorizing the whole photo (like giving a sepia tone to a grayscale image) is a rather straightforward process, changing the color of specific parts of an image can be a bit more tricky. However, Photoshop has a couple of tools that can make this process a relatively easy one. One of the things that make Photoshop such a powerful software is that there are many different ways to achieve a final result, and different photographers have different workflows so it is possible that you can find alternative ways to do this, which is perfectly fine.
Apart from simple photographic interest (like changing the color of a model’s clothes to better match a background or enhancing a specific aspect such as the redness of a sunset), colorizing a subject can be very useful for everyday interests such as visualizing how a house, or a part of it, would look like with a different painting before actually even buying a paint bucket.
Take, for instance, the following photo of a house, downloaded from Pexels, a free stock photography website.
Let’s try to change the color of the door. What allows us to actually change the color of objects without having to worry about each individual pixel is the description of a color not in terms of the RGB channels (the amount of red, green and blue) but in terms of HSI (hue, saturation and intensity). By changing these three factors of a given color, all the textures of the surface we are colorizing will remain intact.
The first method I want to show you here is the use of the Hue/Saturation adjustment layer. Start by duplicating your base layer to make sure that you always have your original image untouched. You can do this by pressing Ctrl+J (in Windows) or by going to the ‘Layer’ menu and clicking on ‘Duplicate Layer…’. Then create the Hue/Saturation adjustment layer by using the menu at the bottom of the Layers panel or by going to ‘Layer’ -> ‘New Adjustment Layer’ -> ‘Hue/Saturation…’.
The next step is to select the color you want to change. While to door is clearly green, by simply selecting the green color in the dropdown menu of the Hue/Saturation panel will do a decent job, but not perfect. This is because the range of colors that Photoshop calls green does not cover the whole range of our photo due to the shadows and differences in lighting. To fix this, use the eyedropper tool with the plus sign located at the bottom of the panel and click at different areas of the door, specially at the corners, where the shadows make the green look darker.
After doing this, if you move the ‘Hue’ slider, you will see how the color of both the door and the window change. You will see that the overall result is quite good, although not perfect. The following image is obtained after increasing the hue to +71.
First of all, some things that we did not want to change actually changed, most notably the window, but also the rock border at the bottom of the house. This is because while selecting the color in the Hue/Saturation panel we also selected colors contained in these two parts of our image (this is quite obvious for the window, but not so for the border). Fixing this is quite simple: you just need to paint with a black brush over those areas in the layer mask (white canvas on the right hand side of the Hue/Saturation layer) that is automatically created with the adjustment layer.
The other problem is on the dark areas of the door, mostly on the top and the bottom right corners and the unevenness of the paint in general. You can almost see the green paint below the blue one. To correct this can become quite complicated and involve a lot of work at a small scale. In general, the Hue/Saturation adjustment layer is a great choice when you have either a relatively flat surface or when you have large variations in contrast that you actually want to keep, like for instance when coloring hair.
For our case, the second option I want to present here makes it possible to get clean result without having to make too many small adjustments. The ‘Color Replacement Tool’ is located together with the ‘Brush Tool’ on the left-hand panel. This tool allows you to sample a color in your photo with a given tolerance and replace it by a pre-selected color, once again preserving the shadows and structure of the area you want to colorize. You can either select the color from the color palette of Photoshop, or hold the alt key with the tool selected and click in any area of your image (or some other image).
The cursor will be now a circle (similar to the brush tool one) but with a small mark at the center. Wherever the mark is, that specific color will be replaced with our pre-selected color, covering all the area marked by the circle surrounding it. This means that if we select a rather large circle, we can put the cursor over any part of the green door without even being careful for the circle not to go outside the door, since Photoshop will make sure that the only colors replaced are those that fall within the color we want to change plus a given tolerance that can be selected by the user.
Notice how, even when selecting a large radius (1170 px) and tolerance (80%), Photoshop is able to cleanly select the pixels that do correspond to the door. While painting over the handle, it makes sense to lower the tolerance a bit and, of course, if you are dealing with a low contrast image (our original image has a high color contrast, which makes the whole process much easier!) you will have to play a bit with this value while going through different areas.
If you look closely, some white areas on the top of the door are also painted in blue. This can be improved, once again, by changing the tolerance or by simply masking out the effect by creating a layer mask and painting over the affected areas with a small brush. The final result after using the color replacement tool over the whole door is shown below.
As you can see, the result is consistent over the shadowed areas as well and in general is much flatter than when using the Hue/Saturation method, something that was desired in this case, although not always. As I mentioned earlier, if you are trying to change the color of areas with a lot of contrast that you want to keep in the end (like for instance hair), the Hue/Saturation method will work better, so whatever your situation is, give both methods a try to find the one that suits you best!