Photo printing is the process of producing a final image on paper for viewing, using chemically sensitized paper. The paper is exposed to a photographic negative, a positive transparency (or slide), or a digital image file projected using an enlarger or digital exposure unit such as a LightJet printer. Alternatively, the negative or transparency may be placed atop the paper and directly exposed, creating a contact print.
Following exposure, the paper is processed to reveal and make permanent the latent image.
Printing on black-and-white paper
The process consists of four major steps, performed in a photographic darkroom or within an automated photo printing machine. These steps are:
Exposure of the image onto the sensitized paper using a contact printer or enlarger;
Processing of the latent image using the following chemical process:
Development of the exposed image reduces the silver halide in the latent image to metallic silver;
Stopping development by neutralizing, diluting or removing the developing chemicals;
Fixing the image by dissolving undeveloped silver halide from the light-sensitive emulsion:
Washing thoroughly to remove processing chemicals protects the finished print from fading and deterioration.
Optionally, after fixing, the print is treated with a hypo clearing agent to ensure complete removal of the fixer, which would otherwise compromise the long term stability of the image. Prints can be chemically toned or hand
colored after processing.
Printing on color paper
Color papers require specific chemical processing in proprietary chemicals. Today's processes are called RA-4, which is for printing
color negatives, and Ilfochrome, which is for printing color transparencies.
Printing from color negatives
Color negatives are printed on RA-4 papers and produce a Type C print. These are essentially the same as
color negative films in that they consist of three emulsion layers, each sensitive to red, green and blue light. Upon processing,
color couplers produce cyan, magenta and yellow dyes, representing the true
colors of the subject. The processing sequence is very similar to the C-41 process.
Printing from color transparencies
Ilfochrome paper uses the dye destruction process to produce prints from positive transparencies. The
color dyes are incorporated into the paper and bleached during processing.
Older papers and processes, like EP2 and R-type are no longer in production.
Printing from a digital image
Digital photography allows, even encourages people to take more photographs. Most of these photos will be viewed on computer monitors, televisions, Digital photo frames, and online Photo sharing sites. Some will be printed at home using Inkjet printers and more specialized Photo printers. For true Photographic prints, image files can be taken to “1 hour” photo finishing locations which have digital minilabs or uploaded to Online photo finishing sites which then mail you your prints. Some Chain stores combine these services allowing you to upload your pictures and specify which local store you want to pick the prints up at one hour later.