I know there are at least a few designers on this site, so this one is for them. If this protip gets popular, or people ask for more, I will gladly start writing these regularly. Otherwise, this will be both the first and last Photoshop tip I write.
Image Injection, not as easy as it sounds.
This is one of the most common uses for Photoshop, but it also seems to be one of the hardest to do well. What many designers don't realize, is that coloring, shadows and highlights are the key to injecting images.
A good starting place is to auto tone/contrast/color the image prior to editing. This will help even out colors, not to mention improve photo quality. Given the image is not a photo, (such as a vector or stock image) You likely won't need to auto tone/contrast/color the image.
Auto tone and others are found in:
Image -> [tool name]
Be sure to position & transform your injection image exactly where/how you want it, before moving on.
For shadows & highlights, the best way to adjust them is to use the
Burn tools in combination with the
Spot Healing Brush and
Blur tools. Don't forget to set the range on the
Burn tools to "Highlights" or "Shadows" respectively.
After the shadows and highlights match, you can clean/match up the edges with the
Erase tools. Keep the erase tool between 10% and 30% opacity and a hardness between 0% and 40%, and it should help cleaning up edges that have bright highlights or deep shadows. Using these tools, as needed, along the edges can really make your injection look like it belongs.
The 2 best ways of adjusting the color of your injection is through either the
Hue/Saturation or through a clipping mask. The
Hue/Saturation method works best on photos, whereas the clipping mask method works best with vector and stock images. In many cases you can benefit from using both methods.
Hue/Saturation Method: Selecting your injected layer, go
Image -> Adjustments -> Hue/Saturation. From here you can adjust the
Master color range or individual color ranges. This makes it particularly easy getting one shade of a color to match another shade of that color.
Clipping Mask Method: If your injection image has a solid color background, or at least nearly solid, this is probably the easiest option for you. Creating a clipping mask with your injection image, and setting the layer mode to
Difference will often produce a near match to what your looking for. Adjust the fill opacity accordingly.
Clipping Mask Method (cont): Additionally, you can clip a solid color to your injection image, and adjust the layer opacity and display mode to help create a match. For example, if injecting into a sepia image, the clipping mask could be a solid dark yellow-orange set to 65% opacity, and a layer mode of
multiply. Given your injection image is already desaturated, you would likely have a near match to the original photo, and would only have to fiddle with the color/opacity to get it spot on.
Below is a picture of the computer I am on now, except I have decided that I don't want to have coderwall on my on my desktop, instead I would like Photoshop. Applying the above, I am able to get a close match.
Remember: The goal is not to get it perfect, but to get it close enough that people won't notice the change unless they are looking for it.
Here is the PSD so you can see for yourself: