My former job at a publishing house, one of my duties was to prepare the digital images for printing using Adobe Photoshop. Here are some of the steps we followed for printing images and a little explanation of why we did it.
Printing images: Know what you are doing!
- Photos and images in general must be converted from RGB to CYMK.
This was usually the first step for printing images and, depending on how many the images were to modify, we would automate the process with an action in Photoshop and then review it. Or we would go manually using fast keyboard shortcuts, if the images were around 10 or less.
Why were we ordered to do this?
In commercial printing, “the technique used to print full-color images, such as color photographs, is referred to as four-color-process or merely process printing. Four inks are used: three secondary colors plus black. These ink colors are cyan, magenta and yellow plus black; abbreviated as CMYK. Same goes for the printer on your desk.” -in Wikipedia’s own words.
In order to be sure that the color output of your image on paper will be as similar as possible to what you see on the monitor you will have to convert to CYMK. Click on “Image -> Mode ->CYMK Color” in Photoshop.
- Images to be printed must be at at least 300dpi.
If you are in the business, it may have happened that some of your clients came to your office with an USB key filled with photos taken directly from internet at ridiculous resolutions and DPI (72, or less, usually) expecting you to place them on their book. Beside the obvious copyright infringement, you will have to explain them that printing images with those file is impossible: the images are too small. Why? Wikipedia helps us again:
“DPI is used to describe the resolution number of dots per inch in a digital print and the printing resolution of a hard copy print dot gain; the increase in the size of the halftone dots during printing. This is caused by the spreading of ink on the surface of the media. Up to a point, printers with higher DPI produce clearer and more detailed output.”
- You don’t print JPEGs. You print .TIFF or .PDF files.
Most people know this already: JPEG is a lossy format. You loose a lot of image data when saving this format. Tiff instead has the ability to store image data in a lossless format. “This makes a TIFF file a useful image archive, because, unlike standard JPEG files, a TIFF file using lossless compression (or none) may be edited and re-saved without losing image quality.” – Wikipedia. Same goes for PDF.
- Choose the paper you are going to print on carefully.
This is something you learn from experience in printing images. The paper you choose to support your printed object has a huge influence on the final output. The best thing to do before printing photos or books is to check the paper personally and consult with an expert at a typography.
Writing a text only book and want to sell it at a low price? A 75gsm (Grams per Square Meter) paper might do the work. Printing a photography book? 150gsm. Postcard? 400gsm.
You have to consider also if you want the paper to be coated or not, glossy or not. As the name suggests, coated paper has a coating, usually of china clay, this gives it a smooth finish. Glossy is a shiny patter that gives more vibrating colors in your images, but reflects a lot of light and gets dirty quite easily with your fingerprints.
Printing images for a photographic exhibition? Try printing on 5mm thick white Forex.