Image forming apparatus

Claim 2

The image forming apparatus according to claim 1, wherein said predetermined order is in general substantial synchronization with the image density signal clock.

Claim 3

The image forming apparatus according to any of the preceding claims, wherein the first conversion property converts a part of the image density input signal corresponding to the low density portion to an image density output signal indicating another range or another value within said other range where an image is developed.

Claim 4

The image forming apparatus according to any of the preceding claims, wherein the selection signal generation means comprises: a first counter (404a, 404g) for counting the main scanning synchronizing signals and outputting a signal showing the number of the main scanning synchronizing signals; memory means (404b, 404h) for storing an initial counter value to determine the phase of the selection signal, and selecting and outputting the initial counter value based on the signal from the first counter; and a second counter (404c) initialized by the initial counter value from the memory means and for dividing the image density signal clock to generate the selection signal.

Claim 5

The image forming apparatus according to claim 4, wherein the selection signal generation means further comprises: signal generation means for generating at least one and preferably plural signals with different phases by dividing the image density signal clock; and selection means for selecting one signal from the plural signals having different phases from the signal generation means based on the output of the memory means, and outputting the selected signal as a selection signal.

Claim 6

The image forming apparatus according to any of the preceding claims, wherein L is the number of gradations of the image density output signal and K is a maximum value of the image density output signal in an area where the first and second image density signal conversion means have different conversion properties, the apparatus satisfies the condition: K/L≦1/2 .

Claim 7

The image forming apparatus according to any of the preceding claims, wherein the image formation means comprises: light beam scanning means for relatively scanning a light sensitive medium with a light beam; an image formation optical system converging the light beam of the light beam scanning means to form a light beam spot of a predetermined size on the light sensitive medium; where d B ≦(1/3)d p , where d p (mm) is the distance between adjacent light beam spots in a main scanning direction on the light sensitive medium and d B (mm) is the light beam spot diameter in the main scanning direction for forming an image when the image density output signal indicates a value within a range in which the image is not developed.

Claim 8

An image forming apparatus comprising: first image density signal conversion means (405, 1505, 1705) for converting multi-valued image density input signal to an image density output signal using a first conversion property; second image density signal conversion means (406, 1506, 1706), which has a second conversion property different from the first conversion property, for converting a part of the image density input signal corresponding to a low density portion to an image density output signal indicating a range where an image may not be developed; conversion/non-conversion discrimination means (1712) for determining whether a conversion by the first and second image density signal conversion means has been conducted on at least one and preferably each group of adjacent image density input signals; signal selection means (1716) for selecting one of the output with conversion, of each group of the image density input signals by the first and second image density signal conversion means and the output, without conversion, of each group of the image density input signals by the first and second image density signal conversion means based on a result of the conversion/non-conversion discrimination means; selection signal generation means (404a-404d) for outputting a selection signal to select the first or second image density signal conversion means in a predetermined order, a phase of the selection signal being shifted for at least each one or more of the main scanning synchronizing signals; pattern signal generation means (401) for generating a pattern signal; phase control means (409) for shifting the phase of the pattern signal generated by the pattern signal generation means for at least each one or more of the main scanning synchronizing signals to form a screen image with a predetermined screen angle; pulse width modulation means (401, 1501, 1701) for outputting a pulse width modulation signal generated by modulating a pulse width of the signal output from the signal selection means using the pattern signal; and image formation means (1-9, 20) for forming an image based on the pulse width modulation signal from the pulse width modulation means.

Claim 9

The image forming apparatus according to claim 8, further comprising: operation means for performing a predetermined operation on at least one image density input signal in each group of adjacent image density input signals to obtain an image density synthesizing signal, and for inputting the image density synthesizing signal to the first and second image density signal conversion means.