JPH07123265A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image forming device able to provide an output of a picture with excellent gradation without increasing a picture data quantity. CONSTITUTION:A multi-valued data conversion section 1 converts external 4-bit density multi-valued picture data into 8-bit density multi-valued picture data and the data are provided to be outputted. A gamma correction ROM 2 applies gamma correction to picture data in 8-bit density outputted from the multi-valued data conversion section 1 to provide an output and a latch 3 latches the data based on a picture clock signal VCLK. A count clock generator 6 generates a count clock signal SCLK whose frequency is 256 times that of the picture clock signal VCLK and the clock signal is counted by a counter 5. A digital comparator 4 compares an output of the latch 3 with an output of the counter 5 to apply pulse width modulation to the picture data after gamma correction and the pulse width modulation signal is used to drive a laser driver (not shown).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, for example, an image forming apparatus for forming an image after gradation correction of a multi-valued image signal.

[0002]

2. Description of the Related Art In a conventional image forming apparatus, its image processing section has a structure as shown in the block diagram of FIG. In FIG. 12, 20 is a gamma (γ) correction R
OM, which inputs image data VIDEO1 to VIDEO4 of 4-bit density (16 gradations) from the outside, and outputs γ-corrected 4-bit image data. FIG. 13 shows an example of the γ correction characteristic of the conventional γ correction ROM 20.

Reference numeral 21 is a latch, which latches the image data that has been .gamma.-corrected by the .gamma.-correction ROM 20 with the image clock signal VCLK. On the other hand, 24 is a counting clock generator,
The count clock signal SCLK that is 16 times the image clock signal VCLK is generated. A counter 23 counts the count clock signal SCLK. That is, one input pixel is one
Since there are 6 gradations, 16 count-ups are performed during one image clock signal VCLK.

Reference numeral 22 denotes a digital comparator, which compares the outputs of the latch 21 and the counter 23 with γ
The corrected image data is pulse-width modulated, and the pulse width modulation signal drives a laser driver (not shown). With the above-described configuration, the conventional image processing unit has performed γ correction.

[0005]

However, as in the conventional case, γ
When the γ correction was performed by the correction ROM 2, the input was 16 gradations, the gradation was not sufficient, and a good image could not be formed. Further, in order to increase the gradation level, for example, when the input image data is replaced with the image data of 4-bit density and the image data of 8-bit density is used, the amount of image data is doubled, and some of the processing Therefore, the overall processing scale becomes large, resulting in high cost.

The present invention eliminates the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide an image forming apparatus which does not impair the gradation without increasing the amount of image data.

[0007]

The present invention has been made for the purpose of solving the above-mentioned problems, and has the following structure as one means for solving the above-mentioned problems. That is, the first
A first gradation image storage means for storing multi-valued image information having gradations of, and a second operation by performing a predetermined operation on the multi-valued image information stored in the first gradation image storage means.
Second gradation converting means for converting into the third gradation, and a third gradation by performing gradation correction on the multivalued image information subjected to the gradation conversion by the second gradation converting means. The image forming means has three gradation converting means and image forming means for forming an image of the multi-valued image information whose gradation is converted by the third gradation converting means. An image is formed from the tone-converted multi-valued image information by a pulse width modulation method, and the third gradation conversion means has at least two gradation correction methods.

[0008]

In the above structure, since the γ correction is performed after the number of gradations is interpolated, an image with good gradation can be output without increasing the amount of image data.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described in detail below with reference to the drawings. <First Embodiment> FIG. 1 is a block diagram of an image processing unit of an image forming apparatus according to the present embodiment. In the figure, reference numeral 1 denotes a multi-value data conversion unit, which receives multi-value image data VIDEO1 to VIDEO4 of 4-bit density from the outside,
The calculation to be described later is performed on it, and 8-bit multi-valued image data is output.

Reference numeral 2 denotes a γ correction ROM of this embodiment, which receives the image data of 8-bit density (256 gradations) output from the multivalued data conversion unit 1 as input and outputs the γ-corrected 8-bit image data. Output. 3 is a latch, and γ correction R
The image data that is γ-corrected by the OM2 is latched by the image clock signal VCLK.

Reference numeral 6 is a count clock generator, which generates a count clock signal SCLK having a frequency 256 times that of the image clock signal VCLK. A counter 5 counts the counting clock signal SCLK between the image clock signals VCLK. That is, 256 are counted up between the image clock signals VCLK.

Reference numeral 4 denotes a digital comparator, which compares the output of the latch 3 with the output of the counter 5 to perform pulse width modulation on the image data after γ correction, and drives a laser driver (not shown) with the pulse width modulation signal. To do. Next, FIG. 2 shows a block diagram showing details of the multi-value data conversion unit 1. In FIG. 2, reference numeral 7 denotes a data storage unit, which stores, for example, 4-bit VIDEOs 1 to 4 input from the outside for three main scanning lines, of which V of 3 × 3 pixels is stored.
1 to V9 are output. FIG. 3 shows the positional relationship between the images V1 to V9. V5 in FIG. 3 is the target pixel.

Reference numeral 8 denotes a conversion operation unit for converting 4-bit data into 8-bit data, which is composed of, for example, a gate array. The conversion operation unit 8 receives 4-bit image data of 9 pixels V1 to V9 shown in FIG.
8-bit image data VDO1 to 8 depending on the values of surrounding pixels
Is output. FIG. 4 is a block diagram showing a detailed configuration of the data storage unit 7 in FIG.

Data for three main scanning lines is held in line memories A to C (9 to 11) and D flip-flops A to C (12 to 14) in synchronization with the image clock CLK, and main scanning 3 × sub scanning. 3 image data V1 to V9 are output.
It is to be noted that the line memories A to C (9 to 11) and the D flip-flops A to C (12 to 14) are respectively combined into two to store multi-valued image data for one line.

FIG. 5 is a flow chart showing the operation of the conversion calculator 8 in FIG. The operation of the conversion calculator 8 is shown in FIG.
And FIG. 3 will be described below. First, step S1
At, the counter n shown in the figure is initialized to "1".
Then, in step S2, it is determined whether the density value of Vn is equal to the density value of the target pixel V5.

When it is determined in step S2 that the density value of Vn is equal to the density value of V5, the process proceeds to step S3, and in step S3, V (10-n) at a position diagonal to Vn in FIG. It is determined whether or not the density value differs from the density value of the target pixel V5 by "1". If the density value of the target pixel V5 is different from the density value of the target pixel V5 by “1” in step S3, the process proceeds to step S8, and the average of the density values of the three pixels arranged on the diagonal line determined is multiplied by 17, that is, (Vn + V (10 −
n) + V5) × 17/3 as 8-bit image data VD
Output as O1-8.

On the other hand, if it is determined in step S2 that the concentration value of Vn is not equal to the concentration value of V5, and in step S3, V (10 at the position diagonal to Vn).
-N) does not differ from the density value of the target pixel V5 by "1", the process proceeds to step S4, and in step S4, V (10-n) which is diagonal to Vn. It is determined whether the density value of is equal to the density value of the target pixel V5. If they are not equal, the process proceeds to step S6.

On the other hand, in step S4, the density value of V (10-n) diagonally opposite to Vn is the target pixel V5.
If it is determined that the density value is equal to
It is determined whether or not the density value of Vn differs from the density value of V5 by "1". If it is determined in step S5 that the density value of Vn differs from the density value of V5 by "1", the process proceeds to step S8, and (Vn + V (10-n) + V5) × 17/3 is output to the image data VDO1-8. And finish.

On the other hand, in step S5, the concentration value of Vn is V
If it is not different from the density value of 5 by "1", the process proceeds to step S6. The process proceeds to step S6 to determine that the diagonal column of Vn is not a pixel column suitable for the conversion calculation. Then, in step S6, "1" is added to the counter n. Next, in step S7, the counter n
Is "5". If the counter n is "5" in step S7, it is determined that all determinations have been completed, the process proceeds to step S8, and all 3 × 3 pixels being processed are replaced with the density value of V5.

If the counter n is not equal to "5" in step S7, the process returns to the determination process of step S2. As described above, in the present embodiment, the surrounding pixels of the target pixel V5 of FIG. 3 are set to V1, V9, V2, V8, V3, V7, V.
4 and V6 are sequentially referred to, and when there is a pixel having the same density value as the target pixel V5, only when the density value of the diagonal pixel differs from the density value of the target pixel V5 by “1”, The average of the values obtained by multiplying the density values of the three pixels on the diagonal line by 17 is output as 8-bit image data VDO1-8.

Next, FIGS. 6 and 7 show examples of converting 4-bit data into 8-bit data in the conversion operation unit 8. FIG. 6 is an example of 5 × 5 4-bit image data, and the conversion processing according to the flowchart of FIG. 5 is performed in the conversion calculation unit 8 by setting the density of pixels around 5 × 5 of FIG. 6 to “0”. And converted into the 8-bit image data shown in FIG.

FIG. 8 shows the γ correction ROM shown in FIG. 1 of the present embodiment.
6 is a diagram showing an example of the γ correction characteristic in FIG. γ correction R
In the OM2, one 8-bit pixel input from the multi-value data conversion unit 1 is converted based on the contents of the address map of the γ correction ROM 2 shown in FIG. As described above, according to the present embodiment, γ correction is performed after interpolating the number of gradations in a non-linear manner, so that an image with better gradation can be formed without increasing the amount of image data.

<Second Embodiment> The second embodiment according to the present invention will be described below. FIG. 10 is a block diagram of the image processing unit of the color image forming apparatus in this embodiment. Figure 1
The same components as those in FIG. 15
Is a counter, which is reset by the print start signal PRNT and is incremented by "1" by the vertical synchronization signal TOP.

Select signals SEL0, S of the counter 15
EL1 is γ together with 8-bit image data VDO1-8
It is input to the correction ROM 2. FIG. 11 shows an address map of the γ correction ROM 2. The 2-bit select signals SEL0 and SEL1 from the counter 15 are 9 bits of the γ correction ROM2.
The address of the γ-correction ROM 2 is selected in the order of magenta, cyan, yellow, and black by inputting to the bit and the 10th bit and the select signal.

Other operations are similar to those of the first embodiment. As described above, according to this embodiment, the same effect as that of the first embodiment can be obtained. First embodiment and second
In the embodiment, an example in which 4-bit data is converted to 8-bit data has been shown, but the present invention is not limited to this, and in the conversion from N-bit data to M-bit data, the relationship of N <M is satisfied. It is useful in all cases where it holds.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0027]

As described above, according to the present invention, γ correction is performed after interpolating the number of gradations, so that an image with good gradation can be output without increasing the amount of image data.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of a first embodiment according to the present invention.

FIG. 2 is a block diagram showing a detailed configuration of a multi-valued data conversion unit of this embodiment.

FIG. 3 is a diagram showing a pixel array in a data storage unit of this embodiment.

FIG. 4 is a block diagram illustrating a detailed configuration of a data storage unit according to the present exemplary embodiment.

FIG. 5 is a flowchart showing processing of a conversion calculation unit of this embodiment.

FIG. 6 is a diagram showing an example of the density of input 4-bit image data according to the present embodiment.

FIG. 7 is a diagram showing an example of the density of output 8-bit image data according to the present embodiment.

FIG. 8 is a diagram showing a γ correction characteristic of the present embodiment.

FIG. 9 is a diagram showing an address map of a γ correction ROM of this embodiment.

FIG. 10 is a block diagram showing an outline of a second embodiment according to the present invention.

FIG. 11 is a diagram showing an address map of a γ correction ROM of the present embodiment.

FIG. 12 is a block diagram showing gradation correction of a conventional example.

FIG. 13 is a diagram showing an example of a γ correction characteristic of a conventional example.

[Explanation of symbols]

 1 Multi-value data conversion unit 2 γ correction ROM 3 Latch 4 Digital comparator 5,15 Counter 6 Count clock generator 7 Data storage unit 8 Conversion operation unit

Claims (3)

[Claims] 1. A first gradation image storage means for storing multivalued image information having a first gradation, and a predetermined value for the multivalued image information stored in the first gradation image storage means. Second gradation converting means for converting into a second gradation by performing calculation, and third by performing gradation correction for the multi-valued image information subjected to gradation conversion by the second gradation converting means. An image forming apparatus, comprising: a third gradation converting unit for converting the gradation into the gradation of 1 .; and an image forming unit for forming an image of the multi-valued image information gradation-converted by the third gradation converting unit. 2. The image forming apparatus according to claim 1, wherein the image forming unit forms an image based on the multi-valued image information whose gradation is converted by the third gradation converting unit by a pulse width modulation method. apparatus. 3. The image forming apparatus according to claim 1, wherein the third gradation conversion unit has at least two gradation correction methods.