JPS61288675A - Picture signal processing device - Google Patents

Abstract

PURPOSE:To determine automatically the optimum gradation correction suitable for the input picture by selecting one correcting means by at least either the highlight point or the dark point set by the setting means. CONSTITUTION:In order to correct the input picture signal by gradation plural gradation corrections ROM 24R, 24G and 24B having the correcting characteristic determined from the gamma of the input picture signal and the gamma of the output system are provided. At least either of the highlight point or the dark point in one screen from the input picture signal is set. By at least either of the set highlight point or the dark point, one of the gradation corrections ROM 24R, 24G and 24B is selected through a control circuit 22.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image signal processing device for outputting an image signal such as a television signal to a 1-tocoby device such as an inkjet printer.

<Prior Art> In this type of device, gradation correction is generally performed in order to smoothly express the highlights to the shadows of an input image.

However, in order to perform optimal tone correction, it is necessary to change the correction curve for tone correction depending on the type of input image, and conventionally, this type of operation required the experience and intuition of skilled engineers. was relying on

On the other hand, the present applicant et al. have developed a method in which highlight points and shadow points are determined from the histogram of the luminance distribution of an image, and tone correction adapted to the image is automatically set based on these two values. Proposal L7.

However, when implementing the above method by converting tables using ROM, for example, 8 highlight points,
In order to prepare 8 shadow points in advance, 64 types of gradation conversion must be prepared.

<Purpose> In view of the above-mentioned problems, the present invention provides an image signal processing device that automatically and more easily sets optimum gradation correction by adapting to various input images.

<Embodiment> The gradation correction method according to the present invention will be explained by taking as an example the case where a television video signal is output to an inkjet printer.

FIG. 1 shows the frequency distribution of brightness of an input image.

Select the highlight point (
Hp), at this time, the gradation correction is performed using the following arithmetic expression as shown in FIG.

Di=Dmaz +Ir,c (tag X z
og Hp ) rin rin, γ. indicates the degree of nonlinearity, and when it is 1, it is linear. Further, the rin of the television signal is 0.45. The value of gamma r1 of the entire input/output system in this conversion is determined as follows.

becomes.

Through experiments with various input images, we have found that the most visually natural output surface can be obtained by setting rt near a certain constant value rth.

Therefore, since Hp is determined and rt is a constant value, the gradation curve can be determined as follows.

DH=rt(zogX-10gHp) FIG. 3 is a control block diagram of the image processing apparatus of this embodiment. The operation will be explained below.

NT8CT V signal-Q input to NT8C input terminal 2
[The signal is demodulated into JG and B color signals by the NTS C de: F-der 6 and input to the changeover switch 12. NT8CT
Vertical with V times signal synchronization separation circuit 8.

The horizontal synchronization signal is separated, and the synchronization signal is transferred to the selector switch 14.
is input to. In addition, R input to the RGB input terminal 4,
The G and B color signals are input directly to the changeover switch 12, and the synchronization signal SY is also inputted directly to the changeover switch 14.

The input signal source specified by the manual input selection switch 10 is then selected by the changeover switch 12.14.

The signal from the input selection switch 10 is the gamma γ of the input signal.
It is also input to the control circuit 22 as a signal for selecting in. The selected R, G, and B color signals are input to analog-to-digital converters (hereinafter referred to as A/D converters) 16FL, 16G, and 16B. On the other hand, the selected synchronization signal is input to the timing signal generation circuit 18, which generates a sampling signal of the A/D converter 16 and line memories 20R and 20G, which will be described later.

Forms a 20B input/output clock. On the other hand, the analog color signal input to the A/D converter 16 is converted into a digital signal and input to each line memory 20. The output signal of each line memory 20 is output to the gradation correction circuit 24R.
,24G.

24B, and R→C, G-+M, B-+Y conversion, gradation correction, and normalization are performed simultaneously.

Here, the characteristics of tone correction are automatically controlled by the control circuit 22. This operation will be described in detail later on C and M whose characteristics have been converted by the 0 gradation correction circuit 24.

The Y data is input to the masking circuit 26, where asymmetric color removal and undercolor removal processing is performed, and each color signal C',
M', Y', and BK' are obtained, and each digital
Analog converter (hereinafter referred to as D/A converter) 280° 28M,
It is converted into an analog signal at 28Y and 288. Each analog signal is applied to the inkjet head via a driver circuit of the inkjet head, for example, to obtain a desired image.

Next, the operation of the tone correction circuit 24 will be explained. Gradation correction circuit 24 performs logarithmic conversion from RGB to each color density CMY, gradation correction, and normalization as described earlier.

This conversion is performed as follows prior to actual image formation.

FIG. 4 shows the television screen 30. 32 in the figure
indicates a horizontal scanning line, 34 sampling directions, 36 sampling points, X indicates the horizontal scanning direction, and Y indicates the vertical direction. Sampling by the A/D converter 16 is performed in a direction perpendicular to the horizontal scanning direction X, and by sequentially moving its position in the horizontal scanning direction, sampling of the entire screen is performed. 640 in the X direction during actual image formation
480 points are sampled in the Y direction. However, since all sampling information is not required for setting highlight points for gradation correction and normalization,
A total of 64 points every 10 vertical lines in the direction, 4 points in the Y direction
Sampling of 80 points is performed.

Furthermore, since the green (G) component accounts for approximately 60% of the luminance signal, only the sampling data of the green signal G is used for the setting.

Assuming that the number of output bits of the A/D converter 16 is 8 bits,
Green digital data takes a value from 0 to 255. The frequency distribution is shown, for example, as shown in FIG. From this frequency distribution, find the integral value, and if the integral value is, for example, 99 of the whole
! Let point X be the highlight point (lowest value of reproduced density) HP.

Using Hp, = rt(10gX-10gHp).

NT8C television signal, Dmax = 1.
When outputting to inkjet No. 5, γt = 0.5 to 0.
．． It is preferable to set it to 7. rt is input.

This calculation may be performed using a computer, but in this embodiment, the gradation correction FtOM 24 performs the gradation correction by table conversion. For example, it has 64 points from HPI to HP64 as processing highlight points, and has 64 types of tables. Then, once the processing highlight point (Hpi) closest to the set highlight point Hp is determined, the corresponding gradation conversion curve written in advance in R and OM according to equation (3) is selected. There is.

Next, a method for selecting an optimal gradation correction curve from the set highlight points))(Pi) will be described.

The gradation correction ROM 24 stores input data R, G, B and output data C9M, Y expressed by the following arithmetic expression.

DB = , rt(10gX1-10gHpR)i=1
．． 2.3 R=1. 2. 3. 4.・・・・・・・・・1
6/=1. 2. 3. 4 Xi = o, ...... 255 However, Xi≧HpRDi = O Xi≦8I)RDi=255 First, as mentioned above, the cumulative density distribution is obtained from the green signal of the input image, and from this Determine the light point Hp.

Next, the processing highlight point Hpi closest to this highlight point HpK is determined 1 to 1, and the corresponding gradation correction curve is selected.

FIG. 5 explains how to obtain the luminance distribution of the luminance signal for the whole. In Figure 5, brightness distribution (0 to 255)
indicates the frequency of occurrence of the A/D converted luminance level (θ~255), and this data is stored in the R in the control circuit 22.
It is stored in AM. First, in step 101, the data area in which data indicating the frequency of occurrence is stored is cleared. Next, in step 102, X is performed on the entire screen.
The loop count in the direction and the X direction is initialized, and then in step 104, 1 is added to the frequency of occurrence of the above luminance level. In step 105, a loop count in the X direction is performed, and if Y>480 (step 106), a loop count in the X direction is performed in step 107, and if Y>
At 640, the process of determining the brightness distribution for the entire frame ends.

Step 109 is the initial setting of the loop count in the X direction.

FIG. 6 is a flowchart for determining the set highlight point I(P) for the input signal from the luminance distribution obtained in the above-mentioned process. 255), and in steps 207 to 215, the HP of the input signal level is determined.

Here, the cumulative total (255) indicates the total cumulative frequency, which is 64×480 due to the number of pixels mentioned above. Also the above point)
In this embodiment, each HP is assumed to be a point greater than 99% of the total cumulative frequency of the luminance distribution for the sake of simplicity. Specifically, a search is performed starting from I-(PH cumulative total (loop)) to find the brightness level immediately before it becomes 99% or less of the total cumulative frequency.

In this embodiment, TTP obtained through the above processing is assumed to be a common HP for each of the R, G, and B signals.

Returning to FIG. 6, first, in step 201, the cumulative total (0 to 2
55) Clear the data area in the RAM where it is stored. Next, in step 202, the cumulative frequency distribution is initialized, that is, the frequency at which the luminance is 0 is set to 17, and in step 203, the loop count is initialized. Step 2
In step 04, the luminance distribution (frequency of occurrence of the luminance level) in the loop is added to the cumulative frequency for the immediately preceding loop, that is, the cumulative total (loop). In step 205, 1 is added to the loop count, and these processes are repeated until the loop becomes -255 (step 206).

Next, KF+ to calculate HP, step 2 (initialize HP in step 17. Steps 213 and 214 calculate cumulative total (255), and subtract loops from 255 until this value becomes 099 or less. 0 Points (loops) that are equal to or less than .99 are defined as highlight points.Highlight points are determined in this manner.

In addition, although the cumulative distribution is obtained from the green signal in the above embodiment, the actual luminance signal Y - Y - 0,59G + 0.3
It is determined by OR+0.11B, and it is more desirable to use Y, but since it requires multiplication and addition processing, there is a problem that it takes a long processing time. The green alone is about 6
Furthermore, experiments in which many types of images were printed revealed that there was almost no significant difference between Y and G.

Furthermore, if a capacity of 2 bits is required for one type of reference table, a correction circuit 24 having 64 types of reference tables is required.
can be configured with a 128-bit ROM. Also, if a reference table is created by ignoring the least significant bit among the 8 bits of the input color signal, the capacity of 1 bit is sufficient for one type of reference table, for example, 16 dark points DPi for processing, Eight highlight points HPi are provided, allowing a total of 128 types of tables. Of course, increasing the ROM size allows for more detailed changes.

Furthermore, although the setting point has been described as the 99% point of the total HP, various points can be selected using the manual image quality adjustment input switch 29.

In this embodiment, the input system is a television signal, and the output system is fixed to an inkjet printer, so the input system has a gamma γin, and the output system has a gamma γ. and maximum concentration I)
max is fixed, but if you want to obtain various selections for the input and output systems, apply a large number of gradation correction characteristics according to each combination, and adjust the gamma of the input system and the gamma of the output system. , and at least one of a highlight point and a dark point. For example, when the output system is fixed, the gradation correction characteristic can be selected using the signal from the input selection switch IO shown in FIG. 3 and the determined highlight point. In this way, 1.
You can select the most suitable gradation correction.

<Effects> As described above, according to the present invention, it is possible to adapt to the input image and automatically determine the optimal gradation correction, so anyone can easily obtain high-quality images without relying on skilled technicians. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a histogram of the input signal brightness level,
Figure 2 is a diagram showing an example of gradation correction characteristics, Figure 3 is a signal processing block diagram, Figure 4 is a diagram showing the relationship between the television screen and sampling position, and Figure 5 is the histogram of Figure 1. FIG. 6 is a diagram showing a flowchart for determining highlight points. Invitation 1 Kasumi

Claims (2)

[Claims] (1) A plurality of correction means having correction characteristics determined from the gamma of the input image signal and the gamma of the output system in order to correct the gradation of the input image signal, highlight points or dark points in one screen from the input image signal An image signal processing apparatus comprising: a setting means for setting at least one of the correction means; and a selection means for selecting one of the correction means based on at least one of a highlight point or a dark point set by the setting means. (2) In claim 1, the selection means selects one of the correction means based on at least one of the gamma of the input image signal, the gamma of the output system, and highlight points or dark points. Image signal processing device.