Photographic 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. Photographs are more commonly printed on plain paper, for example by a color printer, but this is not considered "photographic printing".
Following exposure, the paper is processed to reveal and make permanent the latent image.
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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 neutralising, 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 coloured after processing.
Panalure paper
Kodak Panalure is a panchromatic black-and-white photographic printing paper. Panalure was developed to facilitate the printing of full-tone black-and-white images from colour negatives - a difficult task with conventional orthochromatic papers due to the orange tint of the film base. Panalure also finds application as paper negatives in large format cameras. It is generally not suitable for conventional black-and-white printing, since it must be handled and developed in near-complete darkness.
Kodak has announced that it will no longer produce or sell this product. However, as of early 2006, it is still available from various online retailers.
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Printing on coloured paper
For more info see also: Chromogenic colour print
Colour papers require specific chemical processing in proprietary chemicals. Today's processes are called RA-4, which is for printing colour negatives, and Ilfochrome, for colour transparencies.
Printing from colour negatives
- Colour negatives are printed on RA-4 papers and produce a Type C print. These are essentially the same as colour negative films in that they consist of three emulsion layers, each sensitive to red, green and blue light. Upon processing, colour couplers produce cyan, magenta and yellow dyes, representing the true colours of the subject. The processing sequence is very similar to the C-41 process.
- Rollei make a film called 'Digibase 200 Pro' that is like a conventional C-41 film but it has no orange mask, allowing easy prints on black-and-white paper with a grade 2 or 3 variable contrast filter
Printing from colour transparencies
- Ilfochrome paper uses the dye destruction process to produce prints from positive transparencies. The colour dyes are incorporated into the paper and bleached during processing. Ilfochrome, EP2 and Type R print papers and chemicals are no longer in production.
Source of the article : Wikipedia
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