A & B Roll Printing.
It is sometimes necessary to print a film by more than one pass through the printer; for example when we want to print one image superimposed over another or to make a dissolve, or on 16mm, to hide the splices in the alternate black spacing.
In normal laboratory production A and B roll printing is only extensively used for 16mm film, and for archive purposes this is the most frequent use.
Two separate grading programmes, tapes or bands, are needed for each printing pass, and the print stock must be marked to correspond with the sync mark so as to be able to repeat exactly the same position on the printer for each printing pass.
In this Diagram, you can see the general principle of A/B printing. Two negatives (Neg A and Neg B) are assembled so that the first contains only some scenes, while the rest of the scenes are on the other negative. In the case shown in the Diagram scenes and intertitles are alternatively on Neg A and B. Some blank film is used to replace the missing scenes in the two negatives, so that they are identical and synchronised.
Then the positive print is produced:
first, Negative A is printed on positive print stock,
then the positive is rewound,
Finally, Negative B is printed on the same positive.
The result is that alternatively the scenes from the two negatives will be printed on the positive, which will appear as continuous and complete, as in the diagram.
Applications of A-B Roll printing
Intertitles
A and B roll printing is also used for printing special effects, such as
dissolves and superimposition, especially of titles on picture. There have been
some productions that used multiple rolls to create effects and the maximum
number remembered by one of our authors was eight rolls, A to H!
Rack Correction Printing
Sometimes, A/B roll printing can also be used to produce spliceless dupe negatives of original nitrate materials showing important differences in rack position. This is quite common, particularly between picture and intertitles.
In this case, we will proceed as follows. Original nitrate print will be graded according to duplication needs and rack position. In a first pass through the printer, we will expose only the sections having rack position number 1 (e.g. only the picture). The reel will be rewound, and a second pass will expose only the sections having rack position nr 2 (e.g. only the intertitles). By doing this, we can obtain a complete and spliceless dupe negative, where all different sorts of rack positions will be corrected.