Method of and apparatus for recording image on photosensitive material with a plurality of photobeams

A method of recording an image on a photosensitive material through a scan of said photosensitive material with a plurality of modulated photobeams wherein said scan is conducted along a sequence of main scannings, each of said main scannings being conducted with said plurality of said modulated photobeams in a main scanning direction along periodic scanning lines, said sequence being directed in a subscanning direction, said method comprising the steps of:

• (a) designating a line pitch .DELTA.L of said periodic scanning lines according to a recording plan of said image, said line pitch .DELTA.L being one of a fine pitch .DELTA.L.sub.1 and a normal pitch .DELTA.L.sub.2 which are distingwished from each other by an inequality .DELTA.L.sub.1 <.DELTA.L.sub.2,
• (b) generating image signals expressing said image for each scanning line,
• (c) when said line pitch .DELTA.L which is designated in the step (a) is said fine pitch .DELTA.L.sub.1, performing the steps of:
• (c-1) modulating N photobeams with said image signals to generate N modulated photobeams which form N photospots substantially aligned on said photosensitive material in said subscanning direction at a pitch larger than said fine pitch .DELTA.L.sub.1, wherein N is an integer larger than one, and said N modulated photobeams are classified into front photobeams existing in a side to which subscanning is to be advanced and rear photobeams existing in another side opposite to said side, and
• (c-2) scanning said photosensitive material with said N modulated photobeams along a first sequence of said main scannings while relatively moving said photosensitive material and said plurality of modulated photobeams in said subscanning direction so that scanning lines which are scanned with said front photobeams in a main scanning are positionally alternated with other scanning lines which are scanned with said rear photobeams in another main scanning which follows said main scanning in said first sequence, and
• (d) when said line pitch .DELTA.L which is designated in the step (a) is said normal pitch .DELTA.L.sub.2, performing the steps of:
• (d-1) modulating M photobeams which form M photospots substantially aligned on said photosensitive material in said subscanning direction at a pitch corresponding to said normal pitch .DELTA.L.sub.2, wherein M is an integer larger than one, and
• (d-2) scanning said photosensitive material with said M modulated photobeams along a second sequence of main scannings while relatively moving said photosensitive material and said M modulated photobeams in said subscanning direction so that scanning lines which are scanned in a main scanning are followed by other scanning lines which are scanned in another main scanning which follows said main scanning in said second sequence.

An apparatus for recording an image on a photosensitive material by scanning said photosensitive material with photobeams along periodic scanning lines which substantially extend in a main scanning direction Y and are arrayed in a subscanning direction X being substantially perpendicular to said first direction Y, said apparatus comprising:

• (a) image signal generating means for generating image singals expressing said image for each scanning line,
• (b) beam generating means for generating N photobeams which are modulated by said image signals, wherein N is an integer larger than one, said N photobeams are substantially aligned in said subscanning direction X, and said N photobeams are classified into front photobeams existing in a side to which subscanning is to be advanced and rear photobeams existing in another side opposite to said side,
• (c) main scanning means for relatively moving said photosensitive material and said N photobeams in said main scanning direction Y, to perform main scanning of said photosensitive material repeatedly, wherein N scanning lines are scanned in parallel in each main scanning,
• (d) subscanning means for relatively moving said photosensitive material and said N photobeams in said subscanning direction X by a given subscanning pitch .DELTA.X for every main scanning of said photosensitive material to perform subscanning of said photosensitive material, and
• (e) pitch signal generating means for generating a first pitch signal indicative of a first subscanning pitch .DELTA.X.sub.1 to deliver said first pitch signal to said subscanning means as said given subscanning pitch .DELTA.X, wherein said first subscanning pitch .DELTA.X.sub.1 is determined so that scanning lines which are scanned with said front photobeams in a first main scanning are alternated with other scanning lines which are scanned with said rear photobeams in a second main scanning which follows said first main scanning in repetition of main scanning.