Originally Posted by
McQ
Converting from black and white into color (aka, "colorizing" a b/w image) will always require some interpretive work, primarily because there are many color/hue possibilities that could create a given black and white photo. For some photos this can become quite involved, depending on the number of different objects, the lighting and the original method used to capture the B/W photo in the first place (types of color filters, etc). In short, avoid it if you can!
Perhaps the simplest (although not shortest) way is to manually select each object using the magnetic lasso tool. For each object in the photo, do the following:
(1) Manually select this object (such as a car against a background) using the magnetic lasso tool or whatever else you find easiest
(2) Copy this object and paste it onto the existing black and white image (so that it remains in exactly the same place)
(3) Create a new adjustment layer for this object using Layer>New Adjustment Layer>Hue/Saturation
(4) Once the adj. layer has been created, make sure to check the "Colorize" box on the bottom right of the window
(5) Set the blend mode for this adjustment layer to "color" (as opposed to "normal").
(6) Adjust the hue/saturation sliders until you feel you have a best estimate of the original color
(7) Adjust the brightness and contrast of this layer if needed to improve the look
(8) Repeat steps 1-7 for all other objects/regions in the photo
Overall, do not expect miracles. This can be a very painstaking process and even then, often times colors will look washed out or over saturated without extensive post-processing using levels/curves/channels/etc. If anyone else has suggestions to improve this process that would be great.