Optimizing your images for digital printing
First of all: color spaces Always work in ProPhoto RGB while working on color images, then print in Adobe RGB (1998). This allows the biggest color space to make all color and tonal adjustments. For further color management, invest in a good monitor and calibrate at least once a month. Make sure when you're getting ready to print to use the correct paper profiles from the manufacturer, whether you're using a RIP software or printing through Photoshop. Only use SRGB color space for images on the internet.
For the best black and white images: shoot color
Yes, it sounds counter-intuitive. But when you shoot in black and white (this goes for either film or shooting RAW and processing out to black and white) you don’t have access to all the various tonality in the three color channels. Shoot in color, process out in RGB, and leave your image in RGB color in your layered, working file. Never throw all that info away! You’ll get a much richer black and white image if you work from channels. Try using the black and white adjustment layer or channel mixer to get an image rich in tonality. Only change your image to greyscale in your final flattened file when you are ready to print. (And you always keep your full-sized, layered PSD files separate from your flattened, resized TIF print file, right?)
Sharpening: just enough
Use a light hand when it comes to sharpening – after all, digital photography is relatively new to the world so images that look too clean, crisp and sharp can look fake or overworked.
Here is one option for sharpening that mimics the sharpness of film:
With your image at print size, merge together all visible layers into one on the top layer (ctrl + opt + shift + E). In the layer panels drop down menu, turn the blending mode to soft light. With this layer selected, go to Filters>Other>High Pass, and move the slider on Radius so it is 8 pixels. Set this layer to about 50% opacity (adjust opacity until you like how it looks).
Noise: smooth out transitions
We hate noise in digital files. But, against your best instincts, adding noise in the final stage of editing your image (after sharpening) can help transitions between gradations of tonality. Again, we are used to seeing film grain in photography, and digital images tend to look too clean. Plus, transitions between subtle tones can break up in digital files, and an all-over noise layer can help make the transitions smooth.
On top of your sharpening layer, make a new layer that is soft light blending mode, filled with 50% grey. With this layer selected, go to Filter>Noise>Add Noise. Go with between 6 to 10% noise. Then go to Filter>Blur>Gaussian Blur and set the Radius between 0.6 and 0.8 .
Lastly: make sure the histogram looks good
Always make proofs, even when you think you are sure the file looks perfect, and good luck!