JPH0827497B2 - Color printing device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a color printing apparatus.

[Prior Art] When performing color adjustment in a conventional printer,
The amount of ink such as cyan, magenta, and yellow is individually adjusted, and the gamma characteristic of the whole is manually changed. For this reason, in the above-mentioned conventional apparatus, when adjusting the deviation of the color temperature correction that has occurred at the time of shooting, it takes a lot of time and effort, and in some cases it is impossible to make the adjustment. There is.

[Object of the Invention] The present invention has been made by paying attention to the problems of the above-described conventional apparatus, and in the case where a color temperature setting error occurs at the time of shooting, it is possible to surely and quickly perform good color reproduction. An object of the present invention is to provide a printing device.

[Means for Solving the Problem] The present invention finds the value of a color difference signal at a highlight point and the value of a color difference signal at a dark point in a predetermined digital color image, and calculates the value of the color difference signal at the highlight point and the dark point. The correction amount of the color difference signal according to each luminance value is calculated based on the value of the color difference signal of
One color difference signal is converted into a hue signal and a saturation signal, and C, M and Y signals are output based on the luminance signal, the color difference signal and the saturation signal.

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

In this embodiment, a video printer with an image memory is described as an example.

In this embodiment, a recorder 11 and A / D conversion circuits 12 and 13 are used.
A sync signal control circuit 14, an image memory 20, a line memory 30, a brightness correction circuit 40, a color correction circuit 50, a color signal conversion circuit 60, a masking / black generation circuit 70, and a D / A converter. , Head driver 80, head 81, system controller 90, switch console 91, and each sensor 92
Have and.

The color correction circuit 50 is an example of means for obtaining the value of the color difference signal at the highlight point in the predetermined color image and the value of the color signal at the dark point in the color image, and is also an example of the correction amount calculation means. The correction amount calculating means is a means for calculating the correction amount of the color difference signal corresponding to each luminance value based on the value of the color difference signal at the highlight point and the value of the color difference signal at the dark point.

The color signal conversion circuit 60 is an example of a color signal conversion unit that converts the two color difference signals corrected as described above into a hue signal and a saturation signal. Also, masking and black generation circuit 70
Is an example of a conversion unit that outputs C, M, Y signals (and BK signals if necessary) based on the luminance signal, the color difference signal, and the saturation signal.

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

First, the input NTSC video signal passes through the decoder 11 and is demodulated into a luminance signal Y and two color difference signals RY and BY. The brightness signal Y is converted into a digital signal by the A / D conversion circuit 12 and stored in the image memory 20. The color difference signals RY and BY are line-sequentially switched, A / D-converted, and stored in the image memory 20. The above operation is performed by turning on a freeze switch (not shown) in the switch console 91 and using the sync signal control circuit 14.

 Next, the printing operation will be described.

First, when a print switch (not shown) in the switch console 91 is turned on, the image data in the image memory 20 is read and printing is started based on the read image data.

Specifically, the luminance signal Y read from the image memory 20 is stored in the line memory 30 for one line. Further, since the color difference signals RY and BY are recorded line-sequentially, the missing portion is interpolated, and the interpolated data for one line is written in the line memory 30.
In this case, the same data as the upper data or the lower data may be used without performing the above-mentioned interpolation (so-called twice may be performed).

The luminance signal Y is corrected by the luminance correction circuit 40 to become a luminance signal Y '. The hue signals RY and BY are supplied to the color correction circuit 50.
And the corrected color difference signal RY ′,
BY 'is output and these signals are converted into a color signal conversion circuit.
At 60, the color difference signal H and the saturation signal C are converted.

Then, based on the luminance signal Y ′, the hue signal H, and the saturation signal C, the masking / black generation circuit 70 performs a calculation for correcting the asymmetric color component of the ink, and then the C, M, Y signals (cyan). , Magenta, yellow signal), and outputs the minimum value as the BK signal (black signal). These signals are input to the D / A converter and head driver 80,
Drive pulse waveform signals are output, and the head 81 is driven by these signals to perform printing.

 Next, the operation of the color correction circuit 50 will be described.

First, as shown in FIG. 2, the image memory 20 is 480 × 6.
It is assumed to be composed of 40 pixels. Then, the screen is scanned to find the luminance data of 20 pixels (highlight points) and the color difference data of the pixels in order from the brightest side in the screen, and similarly, the 20 pixels in order from the darkest side. The luminance data of (dark point) and the color difference data of the pixel are found from the luminance data of the pixel.

By the way, generally, with respect to an image in which the white balance is deviated (that is, the color reproduction is broken), the value of the color difference of the pixel can be adjusted to be corrected, whereby the deterioration of the color reproduction is corrected. In this case, the correction amount is determined based on the color difference amount of the pixel considered to be white on the screen or the color difference amount of the pixel considered to be black. Actually, it is difficult to accurately find white or black on the screen, so the brightest point and the darkest point of luminance are respectively the white and black points on the screen.
Think black.

However, if the brightest and darkest values are immediately adopted, there is a high possibility that noise and dropout will be mistaken for white and black. Therefore, some points are sampled from the highlight point (the brighter value on the screen) and the dark point (the darker value on the screen). For example, 480
20 pixels are sampled for each x640 pixels.

The average values of the values of the color difference signals RY and BY for the 20 brighter pixels obtained by these are obtained respectively. Then, the color difference signal R of the highlight point 20 pixels
-The average value of Y is ΔRY (HP), and highlight point 20
Let ΔBY (HP) be the average value of the color difference signals BY of the pixels, and let ΔRY (D be the average value of the color difference signals RY of the 20 dark point pixels.
P) and the average value of the color difference signals BY of 20 dark point pixels is ΔBY (DP).

The correction amounts ΔRY (Y) and ΔBY (Y) for the brightness value Y between the brightness value Y (HP) at the highlight point and the brightness value Y (DP) at the dark point are the brightness value Y at the highlight point. It can be obtained by the weighted average of the difference between (HP) and the brightness value Y (DP) at the dark point. In addition, ΔRY (Y)
Is the correction amount of the color difference signal RY, and ΔBY (ΔY) is
This is the correction amount of the color difference signal BY.

That is, ΔRY (Y) = [ΔRY (DP) {Y (HP) −Y} + ΔRY (H
P) {Y−Y (DP)}] / {Y (HP) −Y (DP)} ΔBY (Y) = [ΔBY (DP) {Y (HP) −Y} + ΔBY (H
P) {Y−Y (DP)}] / {Y (HP) −Y (DP)} These operations are executed for all the luminance signal values (0 to 255). Then, for a luminance value higher than Y (HP), which is the average luminance value of the highlight points, Δ
RY (HP) and ΔBY (HP) are used as the correction amounts, and ΔRY (DP) and ΔBY (DP) are set to the values of the luminance signal whose luminance is lower than the average value Y (DP) of the dark point luminance values. It may be set as a correction amount.

Next, the relationship between the correction amount of the color difference signal RY and the luminance signal Y will be described.

FIG. 4 is a circuit diagram showing the color correction circuit 50 more specifically.

The color correction circuit 50 has a RAM 51 and subtraction circuits 52 and 53.

The RAM 51 uses the color difference signal R− according to the value of the luminance signal Y.
It is a memory for writing the correction amounts ΔRY and ΔBY of Y and BY respectively. Further, the subtraction circuit 52 is for subtracting the correction amount ΔRY from the color difference signal RY, and the subtraction circuit 53 is a circuit for subtracting the correction amount ΔBY from the color difference signal BY. Actually, the subtraction circuits 52 and 53 are composed of ROMs.

 FIG. 5 is a curve showing the characteristics of the RAM 51.

Next, returning to FIG. 1, the operation after the color signal conversion circuit 60 will be described.

The color signal conversion circuit 60 includes correction amounts R-Y 'and B for color difference signals.
The hue signal H and the saturation signal C are output based on -Y '. In this case, the color signal conversion circuit 60 is a table conversion ROM.
It is realized by using.

Based on the corrected color difference signals R-Y 'and B-Y',
When converting to the hue signal H and the saturation signal C, the following equations are used.

H = ARCTAN (R-Y ' , B-Y') C = {(R-Y ') 2 + (B-Y') 2} 1/2 On the other hand, the luminance signal Y is input to the luminance correction circuit 40 One of the conversion curves shown in FIG. 3 is selected according to the values of the highlight point (HP) and the dark point (DP) obtained from the histogram as described above. The luminance signal is processed based on the selected conversion curve.

Then, the masking / black generation circuit 70 converts the gradation-converted luminance signal Y ′, hue signal H, and saturation signal C into C,
Converted to M, Y, BK signals. In this case, the following equation is used.

(RY) = C × SIN (H) (BY) = C × COS (H) R = (RY) + Y ′ B = (BY) + Y ′ G = (1 / 0.59) { 0.3 × (R−Y) + 0.11 × (B−Y)} + Y ′ C = −log (R / R0) M = −log (G / G0) Y = −log (B / B0) BK = MIN ( C, M, Y) Note that R0, G0, and B0 are constants.

When the above calculation results are stored in the table ROM in response to the Y, H, and C signals and the Y, H, and C signals are input,
C, M, Y and BK signals are output. The C, M, Y, and BK signals obtained in this way are converted into analog signals and then drive the head 81 via the head driver 80.
Printing is done.

Further, the switch console 91 is provided with a switch (not shown) for switching the amount of correction of the correction amount calculation means to 0. By turning off this switch, the correction amount of the color difference is controlled to 0 regardless of the histogram information. .

In the conventional apparatus, many print sheets are wasted in order to adjust the color balance, but in the above-described embodiment, this waste can be eliminated.

In the above-described embodiment, 20 pixels are sampled and averaged when obtaining the average value of the highlight points and the dark points, but the number of sampling may be a number other than 20 pixels.

[Advantages of the Invention] According to the present invention, when a color temperature setting error occurs during shooting, good color can be reproduced reliably and quickly.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a diagram showing an example of the image memory in the above embodiment. FIG. 3 is a diagram showing an example of a conversion curve in the brightness correction circuit of the above embodiment. FIG. 4 is a block diagram showing a specific example of the color correction circuit in the above embodiment. FIG. 5 is a diagram showing an example of a characteristic for obtaining the correction amount of the color difference signal with respect to the luminance signal. 50 ... Color correction circuit, 51 ... RAM, 52, 53 ... Subtraction circuit, 6
0: Color signal conversion circuit, 40: Brightness correction circuit.

Claims (2)

[Claims] 1. A means for obtaining a value of a color difference signal of a highlight point and a value of a color difference signal of a dark point in a predetermined digital color image; and a value of the color difference signal of the highlight point and a color difference signal of the dark point. A correction amount calculation means for calculating a correction amount of the color difference signal according to each luminance value based on the value; and a color signal conversion means for converting the two corrected color difference signals into a hue signal and a saturation signal. Based on a luminance signal, the color difference signal, and the saturation signal,
A color printing device, comprising: a conversion unit that outputs C, M, and Y signals. 2. A color printing apparatus according to claim 1, further comprising a changeover switch for setting the correction amount of said correction amount calculation means to zero.