| 摘要 |
A roller is coupled to a movable support frame which in a first position bears a flexible halftone screen which is fully wound up about said roller. As the support frame is translated in a first direction across the film mounted upon a vacuum platen, the flexible screen unwinds and is laid flat across the platen. When the movable support frame is translated in a second direction, the screen is thereafter wound up about said roller somewhat in the manner of a "reverse windowshade.
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