Step 3: Apply the filter effect
By now your Layer palette should look something like this, with the background image at the bottom, the Filter adjustment layer above it, and the Output adjustment layer on top.
If you now double click on the adjustment button of the Filter layer, the three-channel slider window will reappear. Position this on the screen so that you can see most of your picture, and experiment with the Hue and Saturation sliders. For a picture like this one, a Hue setting of around -140 and some increase in Saturation, to around +35 produces a good effect, darkening the sky and lightening the red fenders. Itâ€™s worth noting however that changing the colour balance of the picture in this way will also show up any flaws in the original, such as image noise or JPEG compression artefacts, so the better the quality of your starting image, the better the final results.
When youâ€™re happy with the adjustment, click OK to close the adjustment window, and then go the Layers menu and select Flatten Image to reduce it back down to a single background layer. Save your edited image under a different filename if you want to keep the original colour image intact.
By using this method you can achieve much better results than simply desaturating the colour picture or converting it to greyscale, and since it is still an RGB colour picture you can add other effects such as sepia toning or colour filters.