JPS6230473A - Image printing device - Google Patents

Abstract

PURPOSE:To allot the gradation of proper density according to the luminance distribution of an image data by determining the luminance distribution of the image data and controlling the allotment of the gradation of density for the luminance of the picture image data according to the luminance distribution. CONSTITUTION:When recording is started, input data 1 are read, and the data are stored in an image memory 3 through an interface section 2. Then, a part of data stored in the image memory 3 is sampled by the processing of a CPU 7, a control program memory 8, a RAM etc., and the luminance distribution is calculated. Gradation correction data are prepared according to this calculation, and stored in a TABLE RAM 11. Then data are read out from the image memory 3, and the data are corrected by the operation of the TABLE RAM 11 and a random number generator 10. Then, various data conversion is made by a data converting section 4 and the recording is made by a recording section 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image printer device that records a hard copy of an image having halftones.

[Conventional technology]

When an image with shading is input to an image printer or the like and printed as a hard copy, it is important to properly reproduce halftones in order to improve the image quality.

Generally, when recording a hard copy of an image, it is required to print with a smaller number of gradations than the number of gradations of the original image due to restrictions on the printer side.

A conventional image printer of this type is shown in FIG. In the figure, 1 is input data, 2 is an interface section, 3 is an image memory, 4 is a data conversion section, and 5 is a recording section.

Next, the operation will be explained. Input data 1 is received by interface section 2 . If the input data 1 is an analog signal, it is digitized by the interface section 2. Further, if the input data 1 is a color composite signal, the interface section 2 decomposes it into three primary color data of R, G, and B.

The data passing through the interface unit 2 is temporarily stored in an image memory 3, and the image data read from the image memory 3 is subjected to gamma correction in a data conversion unit 4.

R-G-B/Y-M-C conversion, ink color correction.

Data conversion and the like are performed according to the recording method.

The recording data is then sent to the recording section 5 and converted into a hard copy.

[Problem that the invention seeks to solve]

In conventional image printer devices, when the data converter 4 performs the above-described conversion on image data sent from the image memory 3, the conversion method is fixed. However, some image data have a normal brightness distribution, a flat brightness distribution with a uniform brightness distribution, a high-contrast image where the brightness distribution is concentrated in bright and dark areas with little in the middle, and There are a wide variety of types, such as high-key where the distribution is concentrated in bright areas, and low-key where the distribution is concentrated in dark areas. Therefore, there is a problem in that it is difficult to record images of good quality using a fixed data conversion method.

In other words, the number of color gradations that can be expressed by the image printer device is small compared to the number of color gradations expressed in the transmitted original image, so if the density gradation allocation for recording to image data is not appropriate, the density will change rapidly. This results in the occurrence of false contours, which is the second cause of image quality deterioration.

Therefore, in order to improve image quality, it is necessary to effectively allocate a small number of gradations that can be expressed according to the shading of the original image to smooth changes in recording density.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an image printer device that can allocate appropriate density gradations according to the luminance distribution of image data.

[Means for solving problems]

The image printer device according to the present invention is configured to determine the brightness distribution of image data and control the gray scale assignment of density to the brightness of the image data in accordance with the brightness distribution.

[Effect]

In this invention, a part of the image data is sampled to calculate the luminance distribution in real time, and the density gradation assignment to the image data is automatically controlled according to the luminance distribution so that density changes are smooth during recording. do.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an image printer device according to an embodiment of the present invention. In the figure, an interface unit 21 image memory 3. Data converter 4. The configuration of the recording section 5 is the same as that of the conventional example, but in this embodiment, a correction control circuit (gradation assignment control means) 6 is provided between the image memory 3 and the data conversion section 4. This correction control circuit 6 is a CPU
7. Control program memory8. RAM9. Random number generator 1
It consists of a 0°TABLHRAM 11, which determines the brightness distribution of image data, and controls the density gradation assignment to the brightness of the image data in accordance with the brightness distribution. That is, the correction control circuit 6 allocates a large number of output gradations to a luminance part with a large distribution and a small number of output gradations to a luminance part with a small distribution according to the luminance distribution, and at the same time allocates a small number of output gradations to a luminance part with a small distribution. The number of gradations of the output gradation level corresponding to the gradation level is set to be 1 or more, and the corrected image data is output to the data conversion section 4. Note that this first
In the figure, 12 is an address bus, and 13 is a data bus.

Next, the operation will be explained using the flowchart shown in FIG. After performing initial settings 14, the image printer device waits until recording starts (step 15).

When recording starts, the input data 1 is read and stored in the image memory 3 through the interface unit 2 (step 16).

Next, CPU7. Control program memory8. A part of the data stored in the image memory 3 (10% or less of the total data) is sampled by processing in the RAM 9, etc., the brightness distribution is calculated, gradation correction data is created according to this, and this is sent to the TA.
The correction table value is stored in the BLE RAM 11 (step 17). The above is the process of creating the correction table value. Next, data is sequentially read from the image memory 3 and stored in the TABLE RAM 1.
1 and the operation of the random number generator 10 (step 18). Thereafter, the data conversion section 4 performs various data conversions (step 19), and the recording section 5 performs recording (step 20).

An example of associating gradation curves from luminance distribution is shown in FIGS. 3 and 4. In the figure, the relationship between density and brightness is treated as follows.

(Density) = (Full scale of brightness) - (Brightness) Figure 3 (
al is an image whose brightness is centered on dark areas, and the gradation curve 21a is such that the recording gradation level rises rapidly in high density areas. In the same figure ('b), the brightness is centered on the bright area, and the gradation curve is 2.
1b is such that the recording gradation level rises rapidly in the low density area.

Furthermore, the gradation curves for an image with a normal luminance distribution and an image with a flat luminance distribution are shown in FIG. 4(a), respectively.

(The result is as shown in bl. In other words, in the conventional device, the gradation curve 21d shown in FIG. 4('b) was linear regardless of the brightness distribution of the image data. In this method, the luminance distribution of image data is investigated, and the gradation curve 21 is controlled to be non-linear in accordance with the luminance distribution in order to allocate fine density gradations to areas where the luminance of the image data is concentrated. There is.

Next, a specific example of creating a synopsis correction table value from the luminance distribution and performing gradation correction will be described with reference to FIGS. 5 to 7. This example is a case where the number of input gradations and the number of output gradations are both 8 gradations (taking values from 0 to 7). Assume that the histogram showing the frequency D (Y) with respect to the luminance Y obtained from the sampling data is shown in FIG. (Figure 5(b))
. Then, as shown in Figure 5(C), input Y and output K2O(
1) can be associated. Output O for input O
9 For input 1, output is 0 (50%) or 1 (5
0%).

For input 2, output 1 (33%) or 2 (67%
) etc.

According to this correspondence, TABLHRAM1 shown in FIG.
Create a storage value for l. Here is the address Az.

The 3 bits of AI and A correspond to the number of input gradations, and the AI,
The 2 bits of Ao control the input/output correspondence stochastically.

First, since output 0 is associated with input O with a probability of 100%, it is assumed to be 0 regardless of the values of A o and A +. For input 1, output is 0 and 1, respectively 50
% probability, so when A1, Ao ``'00,01, it is O, AI, and when Ao = 10.11, it is 1. Thereafter, the number of output gradations is similarly determined according to the probability.

When image data is sequentially passed through the TABLE RAM 11 for gradation correction, data from the random number generator 10 is input to addresses Ao and At (FIG. 7). random number generator 10
Both Ayu and AI are 0. Assuming that 1 occurs with a probability of 50%, AIAo generates 00°01.10.11 with a probability of 25% each.

Therefore, four types of output gradation levels are selected with equal probability for each input gradation level. For example, when the input is 1, O,
Four types, 0, 1, and 1, are selected with equal probability, and 50% of the results are determined to be O, and 50% are determined to be 1.

The following effects can be expected from the device of this embodiment.

(1) Since the configuration is such that density gradation assignment corresponding to the luminance distribution of image data is automatically performed, it is possible to record an image with smooth density changes and no false contours during recording.

(2) Processing time can be shortened by using a small amount of sampling data to obtain a correction curve for tone assignment.

(3) Even if the number of gradations in the original image is small, since the correction control circuit includes a random number generator, the number of gradations can be increased during recording.

In the above embodiment, the case where the number of input gradations is equal to the number of output gradations is shown, but the present invention can be applied even when the number of output gradations is greater than the number of input gradations. Further, in the above embodiment, when assigning the input level to the output level, a value obtained by multiplying the cumulative brightness number ΣD (1) by the constant K is used, but the present invention is not limited to this, and various configurations may be used. is possible.

Furthermore, although the above embodiment has an image memory inside the image printer, this image memory is not an essential component of the printer. In addition, referring to recording methods, the present invention includes melting type or sublimation type thermal transfer recording, color development type thermal recording.

It can be widely applied to recording methods that have gradation reproduction ability, such as ink shared methods.

〔Effect of the invention〕

As described above, according to the present invention, density gradation assignment corresponding to the luminance distribution of image data is automatically performed, so that it is possible to record an image with smooth density changes and no false contours during recording. Furthermore, since the number of output gradations is equal to or greater than the number of input gradations during gradation assignment control, smooth recording of density changes can be achieved even when the number of gradations in the original image is small.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an image printer according to an embodiment of the present invention, FIG. 2 is a flowchart showing the operation of the printer, FIG.
a) (bl is a gradation curve diagram showing the luminance distribution of image data and the density gradation level corresponding thereto, Fig. 5 fA
) fbl (C) is a diagram for explaining the procedure for creating gradation correction data from luminance distribution, Figure 6 is Figure 5 + a)
FIG. 7 is a diagram showing a part of the correction control circuit, and FIG. 8 is a block diagram showing a conventional image printer device. 1... Input data, 6... Correction control circuit, 7...
CPU, 8... Control program memory, 9... RA
M, 10...Random number generator, 11...TABLE R
A.M. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) In an image printer device that records a hard copy of an image having halftones, a brightness distribution output means for sampling a part of input image data to obtain a brightness distribution of the input image; Accordingly, the number of output gradations is increased to the luminance part with a large distribution, and the number of output gradations is decreased to the luminance part with a small distribution, and the output gradation level corresponding to the input gradation level with image data is set to 1 or more. 1. An image printer apparatus comprising: gradation allocation control means for outputting corrected image data with a number of gradation levels. (2) The image printer apparatus according to claim 1, wherein the gradation assignment control means performs gradation assignment control on digital image data by digital processing.