JPH07115497B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

[Prior Art] A conventional printer that creates a histogram after performing automatic gain control on an input image signal and performs automatic gradation correction has an AGC circuit. This AGC circuit uses a timer or the like to I am trying to scan the screen.
That is, in the above-mentioned conventional apparatus, the AGC circuit itself scans for one screen, automatically determines the amplification factor based on the maximum value of the input signal level, and adjusts the input signal level. Is used to correct the gradation.

That is, since the input signal level changes variously depending on the image output device or the image itself, if the input signal is printed out as it is, the print image has no gradation or the print image has a biased density distribution. AGC (automatic gain control) is performed to create a print image that has gradation and has no uneven density distribution.
The gradation is being corrected.

However, in the above conventional device, the sampling point of the AGC circuit is determined according to the configuration of the AGC circuit, and the sampling point is uniquely determined, so that it may not be possible to perform appropriate gradation correction. There is.

That is, when character data is included in the image to be printed, the character data portion greatly affects the AGC. However, in the conventional apparatus, regardless of the presence or absence of the character data portion, the sampling points are taken at the predetermined intervals, so that proper AGC may not be performed in some cases.

[Object of the Invention] The present invention has been made in view of the above points, and an object of the present invention is to provide an image forming apparatus capable of performing good automatic gain control regardless of the type of an input image. is there.

In order to achieve this object, the image forming apparatus of the present invention,
Instructing means for instructing a desired input image signal in the input image signal as a sampling point of the input image for performing automatic gain control on the input image signal, and the desired input instructed by the instructing means. Determining means for determining a control level for performing the automatic gain control using an image signal; and image forming means for forming an image according to an input image signal corrected based on the control level determined by the determining means. Is to have.

Embodiment of the Invention FIG. 1 is a block diagram showing an embodiment of the present invention.

In this embodiment, an AGC (automatic gain control) circuit 1 for changing an amplification factor according to an input image signal level and an A / D conversion circuit 2 are provided.
, A normalizing circuit 3 for performing gradation conversion, and a memory 4
An image processing circuit 5, a head driver 6, a print head 7, a system control circuit 8, and an operation unit 9 such as a switch.
And a sensor unit 10 and a motor driver 11.

The system control circuit 8 indicates a sampling point for automatic gain control.

Next, the operation of the above embodiment will be described.

FIG. 2 is a flow chart showing the operation of the above embodiment.

First, perform the initial setting of the prescanning group (S
1) When a print request is issued from the operation unit 9 to the system control circuit 8, the system control circuit 8 starts the prescanning operation to set the level of the AGC circuit 1.

The AGC circuit 1 fetches and stores the level of the image signal at the sampling point designated by the system control circuit 8 (S2). And during prescanning,
The previously stored signal level is compared with the magnitude of the signal level at each sampling point, a large value is stored, and the same operation as above is repeated at the next sampling point, the next sampling point, ... (S3, S4). And after the pre-scanning, AGC
The amplification level of the circuit 1 is set (S5).

After that, initialize the histogram loop (S
6) Input the same data as S2 (S7), and the system control circuit 8 performs gradation conversion operation by the histogram method of the print image (S8) and repeats this for one loop (one horizontal scanning line). (S9, S10). Then, the normalize curve of the normalize circuit 3 is selected, and the gradation correction of the input image data is performed. That is, a search for highlight points and shadow points is performed (S11), and based on the densities of these highlight points and shadow points,
A gradation curve is selected according to the gradation conversion table, and the gradation of the input image data is corrected.

Then, the memory 4, the image processing circuit 5, the head driver 6
Through, the head 7 is driven to obtain an image print.

In the above embodiment, the system control circuit 8 instructs the sampling point of the AGC circuit 1 to check the level of the input image signal at an arbitrary point, and to determine the amplification factor of the AGC circuit 1. . Specifically, for the character portion, the system control circuit 8 does not instruct the sampling point, but the portion other than the character does not instruct the system control circuit 8 to indicate the sampling point.

By doing so, the influence of AGC due to the character portion is eliminated, and proper AGC can be performed.

Further, in the above embodiment, since the AGC circuit 1 does not need to have means for performing scanning such as a counter,
The circuit configuration of the circuit 1 is simplified.

EFFECTS OF THE INVENTION According to the present invention, the instructing means can instruct any sampling point in the input image signal, so that the sampling point is not uniquely determined, and automatic gain control is performed for any type of input image. There is an effect that can be appropriately performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a flow chart showing the operation in the above embodiment. 1 ... AGC circuit, 3 ... Normalize circuit, 8 ... System control circuit.

Claims (1)

[Claims] 1. An instruction means for instructing a desired input image signal in the input image signal as a sampling point of the input image for performing automatic gain control on the input image signal; Determining means for determining a control level for performing the automatic gain control using the desired input image signal; and image formation according to the input image signal corrected based on the control level determined by the determining means. An image forming apparatus comprising: an image forming unit that performs the image forming unit.