JPH02145366A - image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that receives a multivalued image signal, performs gradation correction on the signal, and then prints a multitone density print. .

[Prior Art] FIG. 8 is a block diagram of an image processing section of a conventional image forming apparatus. In FIG. 0, 11 is a gamma (γ) correction RO.
M, inputs 4-bit density (16 gradation) image data VIDEOI to VIDEO4 from the outside and outputs 4-bit image data subjected to γ correction. FIG. 9 shows the γ correction characteristic of an example of the prior art. A latch 12 latches the γ-corrected image data using the image clock signal VCLK.

On the other hand, 15 is a counting clock generator, and the counting clock signal 5C has a frequency 16 times that of the image clock signal VCL.
Generates LK. 14 is a counter, which counts the counting clock signal 5CLK. That is, since one input pixel has 16 gradations, the image clock signal VCL is counted up 16 times. 13 is a digital comparator;
The image data after γ correction is pulse width modulated by comparing the outputs of the latch 12 and the counter 14, and a laser driver (not shown) is driven by the pulse width modulation signal.

[Problem to be solved by the invention] However, when γ correction is performed as shown in the conventional figure 9, the input becomes 1
Even though there are 6 gradations, the output is actually 10 gradations.

The present invention is intended to eliminate the drawbacks of the prior art described above, and its purpose is to provide an image forming apparatus with a simple configuration that does not impair input gradation.

[Means for Solving the Problems] In order to achieve the above object, the image forming apparatus of the present invention has the following features:
In an image forming apparatus that receives a multi-value image signal, performs gradation correction thereon, and then performs multi-tone density printing, M bits representing 2N gradations are obtained by performing non-linear gradation correction on the N-bit multi-value image signal. The outline thereof is to include a gradation correction means that outputs a multivalued image signal (M>N).

Preferably, one aspect thereof is to perform printing with multiple gradation densities using a dither method.

Preferably, one aspect thereof is to perform multi-gradation density printing using a pulse width modulation method.

[Function] In such a configuration, the gradation correction means performs nonlinear gradation correction (for example, γ correction) of the N-bit multivalued image signal to produce at least M bits (M>N) representing the same 2N gradations as the input.
outputs a multivalued image signal. This increases the resolution of the output (the number of bits M) in accordance with the slope of the nonlinear gradation correction curve, thereby forming an output that does not impair the number of gradations of the input.

Preferably, multi-tone density printing is performed using a dither method or a pulse width modulation method.

[Description of Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of an image processing section of an image forming apparatus according to an embodiment. In the figure, 1 is a γ correction ROM,
4-bit density (16 gradation) image data VID from external source
It inputs EO1 to VIDEO4 and outputs γ-corrected 6-bit image data.

A latch 2 latches the γ-corrected image data with the image clock signal VCL. A counting clock generator 5 generates a counting clock signal 5CLK having a frequency 64 times that of the image clock signal VCL. A counter 4 counts the count clock signal SCL between the image clock signals VCLK. That is, the image clock signal VCL
64 counts are added between K. 3 is a digital comparator which performs pulse width modulation on the γ-corrected image data by comparing the outputs of the latch 2 and the counter 4;
A laser driver (not shown) is driven by the pulse width modulation signal.

FIG. 2 is a diagram showing an example of the γ correction characteristic of the embodiment. In the figure, one input pixel has 16 gradations (OH"Fo), which is converted using a predetermined γ characteristic and the γ characteristic is sampled at a resolution of 64. Therefore, one input pixel has 16 gray levels (OH"Fo).
The 6 gradations do not lose their gradation properties even after γ correction, and are output as 16 gradations (00) 1 to 3 CH) using 6-bit data.

FIG. 4 shows an address map of the γ correction ROM of the embodiment.

FIG. 3 is an operation timing chart of the configuration shown in FIG. In the figure, there are 64 counting clock signals 5CLK within one period of the image clock signal VCLK. The counter 4 outputs oOH in each cycle of the image clock signal VCL.
~3F, forming a so-called sawtooth wave. On the other hand, the output of latch 2 changes every cycle of image clock signal VCL. There are 16 types of change values. The comparator 3 compares the output of the latch 2 and the output of the counter 4, and outputs a logic level signal only in the period in which the output of the counter 4 exceeds the output of the latch 2. As a result, a so-called PWM signal having a pulse width (16 gradations) corresponding to the density of the image data is obtained.

[Other Embodiments] FIG. 5 is a block diagram of an image processing section of an image forming apparatus according to another embodiment. Components that are the same as those in FIG. 1 are given the same numbers. In the figure, 6 is a γ correction ROMI, which has, for example, the γ conversion characteristic shown in FIG. 9, and outputs 4-bit data using 4-bit manual input. The 4-bit output is input to the upper 4 bits of the digital comparator 3 via the latch 2. 7 is a γ correction ROM 2, which has conversion characteristics as shown in the address map in FIG.
Output bit data. The 2-bit output is input to the lower 2 bits of the digital comparator 3 via the latch 2. The digital comparator 3 pulse width modulates the γ-corrected image data by comparing the outputs of the latch 2 and the counter 4, and drives a laser driver (not shown) with the pulse width modulation signal.

FIG. 7 is a diagram showing an example of γ correction characteristics in another embodiment.

In the above embodiment, the output density is PWM modulated, but the present invention is not limited to this. Other methods such as dither processing may also be used.

[Effects of the Invention] As described above, according to the present invention, γ correction can be performed without reducing the number of gradations, and an image with good gradation can be output.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram of the image processing section of the image forming apparatus of the embodiment, FIG. 2 is a diagram showing an example of the γ correction characteristic of the embodiment, and FIG. 3 is an operation timing chart of the configuration of FIG. 1. FIG. 4 is a diagram showing the address map of the γ correction ROM of the embodiment, FIG. 5 is a block diagram of the image processing section of the image forming apparatus of another embodiment, and FIG. 6 is a diagram of the γ correction ROM 2 of the other embodiment. FIG. 7 is a diagram showing an example of γ correction characteristics in another embodiment. FIG. 8 is a block diagram of an image processing section of a conventional image forming apparatus. FIG. 9 is a diagram showing conventional γ correction. FIG. 3 is a diagram showing an example of characteristics. In the figure, 1... γ correction ROM, 2... latch, 3...
・Digital comparator, 4... Counter, 5...
Counting clock generator, 6...γ correction ROMI, 7...
- γ correction ROM2. Scatter (H) ADDRESS Fig. 6 ROM manual entry (H) Fig. 9

Claims (3)

[Claims] (1) In an image forming apparatus that receives a multi-valued image signal, performs gradation correction thereon, and then prints at a multi-gradation density, non-linear gradation correction is performed on the N-bit multi-valued image signal.
An image forming apparatus comprising a gradation correction means for outputting an M-bit (M>N) multivalued image signal representing N gradations. (2) The image forming apparatus according to claim 1, wherein printing of multiple gradation densities is performed by a dither method. (3) The image forming apparatus according to claim 1, wherein multi-tone density printing is performed using a pulse width modulation method.