JPH05328280A - Video printer - Google Patents

Abstract

PURPOSE:To print an individual picture with a proper density in a multi-picture printing. CONSTITUTION:In the case of 25-picture plane printing, an LPF 26 is used to eliminate a high frequency component of input picture and 25 sets of individual picture data are stored in memories 40, 42, 44. The picture data are read and converted into an RGB signal by an RGB matrix circuit 52. A Y signal is selected by a changeover switch 54 and stored in a line memory 60 by one line. A system control circuit 72 detects a maximum value and a minimum value from luminance data in the line memory 60 at every individual picture to let them be a highlight point(HP) and a dark point(DP) of the individual picture. In the case of printing of B, G, R, the data of the HP, DP, B, G, R of the individual picture are fed to a gradation conversion ROM 64, in which the gradation is converted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video printer, and more particularly to a video printer which prints out multiple images.

[0002]

2. Description of the Related Art A video printer is a video tape
This is a device for printing out one screen of a video signal or a television signal output from a recorder (VTR) or a still video reproducing device on paper as a still image. Video equipment that outputs a video signal must have a white level of 100% and //
Alternatively, the black level is different for each device, and a signal of different brightness is output depending on the shooting scene.

When the levels of the input video signals are different, the following problems occur in the video printer. That is, when 100% white is set to the maximum white (no print), the bright part may be greatly skipped (no print) or the bright part may be printed in light gray depending on the connected video equipment. The overall impression may be dark. Also, for dark areas,
When a video signal with a high black level is input, the darkest part of the image is printed lightly.

For this, a method of providing a knob for finely adjusting the brightness and the contrast manually can be considered, but it is necessary to repeat the test printing a plurality of times and must be proficient. The sex is bad.

Further, in the still image to be printed, the brightest part and the darkest part are detected, the brightest part is not printed, and the darkest part is black (printing with maximum density) so that gradation conversion is performed. There is also a configuration. For example, the luminance signal of a still image is appropriately sampled to form a luminance histogram. The brightness levels of 1% and 99% of the cumulative value of this histogram are obtained, and the brightness level of 1% is set as the dark point (DP) and the brightness level of 99% is set as the highlight point (HP). Then, tone conversion is performed so that the DP brightness level is black with the maximum density and the HP brightness level is non-printing. The reason why 1% and 99% are adopted is to eliminate a sudden influence due to noise.

FIG. 2 shows an example of sampling for an image of 640 pixels × 480 lines. 16 pixels horizontally and 2 pixels vertically are sampled. Since the peripheral part is often not important, sampling is performed from a range of about 80% excluding the peripheral part in both the horizontal and vertical directions. The sampled luminance signal is quantized into, for example, 6 bits to create a histogram. An example of the histogram is shown in FIG.

As the gradation conversion, the RGB signal indicating the lightness is naturally logarithmically converted into the CMY value which is the density. In order to print no more than HP and print all less than DP at maximum density,
Each value of R, G, B is linearly converted between HP and DP, and if the value after linear conversion is 1 or more, it is set to 1, and if it is 0 or less, it is set to 0.
And The RGB values thus corrected are subjected to natural logarithmic conversion. The curve 10 in FIG. 4 is the RGB-to-CMY characteristic curve before correction, and the curve 12 is the RGB-to-CMY characteristic curve after correction.

The video printer uses the input video signal to
An image memory for capturing and storing a screen to be printed is provided. The above brightness histogram is calculated from the brightness data stored in the image memory.

The video printer also has a function of reducing and storing a plurality of images in the image memory and printing them simultaneously.
It is known that a so-called multi-image printing can be performed. For example, FIG. 5A shows an example of 4-screen multi-image printing, and FIG. 5B shows an example of 25-screen multi-image printing. The image memory has a capacity for storing image data for one screen (for example, 6
Since there are only 40 pixels x 480 lines), in the case of 4 screens, it is thinned out to 1/2 in the horizontal and vertical directions, and
It is stored in the image memory as shown in (a), and in the case of 25 screens, it is thinned out to 1/5 in the horizontal and vertical directions and stored in the image memory as shown in FIG. 5 (b).

[0010]

In the case of this multi-image printing, the above-mentioned automatic gradation conversion function causes a problem. That is, the conventional automatic gradation conversion function forms a brightness histogram by using the entire multi-image as one image, and performs gradation conversion according to the calculated HP and DP. However, the DP and HP of the individual images forming the multi-image rarely match the DP and HP of the entire multi-image. For example,
In a multi-image of 4 screens, one individual image is bright and the other 3
When one individual image is dark, in the conventional example, HP becomes the brightest value of the bright individual image, only the bright individual image is printed with proper brightness, and the other three are printed dark, which is not preferable as a whole. Will be printed.

Further, in the case of four-screen multi-value image printing, when there are only three individual images to be printed, it is general to write the maximum value in the image memory for the remaining one. However, in this case, the gradation is converted regardless of the brightness of the three individual images to be printed, and a print with an appropriate density cannot be obtained.

A still video floppy can store up to 50 images as standard, and 2 as an index.
In many cases, five sheets are collectively reproduced and output to a monitor or a video printer. In the case of a still video floppy, recorded tracks and unrecorded tracks are likely to coexist, and even in the above-described multi-image printing, individual images to be printed are likely to be missing.

It is an object of the present invention to provide a video printer which solves such problems.

[0014]

A video printer according to the present invention is a video printer for printing a multi-image composed of a plurality of individual images, and calculates a highlight point and a dark point of the individual image. It is characterized in that a calculating means and a gradation converting means for converting the gradation of the individual image according to the highlight point and the dark point calculated for each individual image are provided.

[0015]

By the above means, each individual image is converted into a gradation suitable for each image. As a result, each individual image is printed with an appropriate density.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

First, the basic idea of the present invention will be described.

In the case of multi-image printing with a relatively small number of screens such as four screens, a histogram is created for each individual image and HP and DP for each individual image are calculated. For example,
As shown in FIG. 6, for each of the four individual images, the luminance data is sampled every 8 pixels in the horizontal direction and every 2 pixels in the vertical direction within a range of 80%.

In the case of one-screen printing, every 16 pixels in the horizontal direction and every 2 pixels in the vertical direction are sampled.
In the case of a 4-screen multi-image reduced to 2, half of the case of 1 screen is best every 8 pixels in the horizontal direction and every other pixel in the vertical direction, but since the print size of one image is small, HP and The calculation accuracy of DP is also good, and the horizontal direction is 8
Every other pixel, every two pixels in the vertical direction.

A histogram is created from the sampled luminance data, and HP and DP for individual images # 1, # 2, # 3 and # 4 are calculated. Individual images # 1, # 2, #
The gradations of 3 and # 4 are converted according to the respective HP and DP. This gradation conversion may be performed while printing. When there is a portion that is not printed in the multi-image, the data in that portion has the maximum value as described above, so it does not affect the HP and DP of other individual images and does not affect the print result.

Next, the processing in the case of multi-image printing having a large number of constituent screens such as 25 screens will be described. In this case, if the histogram is taken for each individual image and HP and DP are calculated, it takes time to calculate, and the gradation conversion is completed within a few seconds from when the paper is supplied until printing becomes possible. Is difficult.

Further, in the case of 25 screens, when each of the 25 screens is simply sampled every 5 pixels in the horizontal and vertical directions, written into the image memory, read out and printed, the mosaic pattern is formed by the remaining high frequency components. Will be printed. To prevent this, LPF (low pass
A filter may be used to cut the high luminance range in both the horizontal and vertical directions to reduce the band to about 1/5, and then sampling may be performed. The LPF also removes abrupt noise included in the input video signal, so that the maximum value and the minimum value of the brightness are simply displayed on the HP without taking a histogram.
And DP is no problem. This is also because the print size of the individual image becomes small and the detection accuracy of HP and DP may be weakened.

FIG. 7 shows an example of sampling when a multi of 25 screens is displayed. The sampling range is about 80% in both the horizontal and vertical directions. Similar to the case of four screens, sampling is performed every 8 pixels in the horizontal direction and every 2 pixels in the vertical direction. This is because the brightness levels are averaged by the LPF, and because the print size is small, the HP and DP detection accuracy may be weak.

For each individual image, the maximum value of the brightness data is HP and the minimum value is DP. This is simply a size comparison process, and can be completed in a much shorter time than the histogram creation process. The 25 HPs and DPs obtained are used to perform gradation conversion for each individual image and print. Of course, HP and DP
If the printing is performed while switching the gradation conversion and performing the gradation conversion, the time required for the printing can be shortened.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention applied to a sublimation type thermal transfer type video printer. The input signals are a composite video signal and a luminance / chroma separation type video signal.
Separates the composite video signal into a luminance signal and a chroma signal, and changeover switches 22 and 24 switch between the luminance and chroma outputs of the video decoder 20 and the luminance signal and the chroma signal of the luminance / chroma separation type video signal. ..

The LPF 26 removes high frequencies from the luminance signal output from the switch 22 and outputs a luminance signal for multi-screen of 25 screens. A circuit example of the LPF 26 is shown in FIG. A high frequency band is removed by the LPF 80, and a delay of one line is delayed by the delay line 82 of one line. With the adder circuit 84,
The signals of adjacent two lines are added, and 1 is obtained by the divider 86.
The average is set to / 2.

The change-over switch 28 is used for one-screen printing or four-screen printing.
In the case of screen printing, the output of the changeover switch 22 is selected, and in the case of 25 screen printing, the output of the LPF 26 is selected. The color difference conversion circuit 30 converts the chroma signal output from the changeover switch 24 into two color difference signals RY and BY.

The A / D converters 32, 34 and 36 are the luminance signal Y from the changeover switch 32 and the color difference conversion circuit 30.
The color-difference signals R-Y and B-Y from are converted into digital signals, and the memory control circuit 38 stores them in the corresponding Y memory 40, RY memory 42, and BY memory 44, respectively. In these memories 40, 42, 44, one-screen printing, four-screen printing, and 25-screen printing are respectively performed.
Image data of 1 screen, 4 screens and 25 screens is stored.

Image data necessary for printing is stored in the memories 40 and 4.
2, 44, the data is read out, and the D / A converter 4 is read.
6, 48, 50 convert into an analog signal. RG
The B matrix circuit 52 includes D / A converters 46, 48, 50.
RGB signal is formed from the output of
Selects sequentially the luminance signal output from the D / A converter 46 and the B, G, R signals output from the RGB matrix circuit 52. A sublimation thermal transfer printer generally prints in a frame sequential manner.

The Y signal is first selected for the above-mentioned histogram processing, and the selected Y signal is the A / D signal.
The line memory 60 is converted into a digital signal by the converter 56, and one line is transferred to the line memory 60 via the memory control circuit 58.
Written in.

In the case of one-screen printing, predetermined pixel data is sampled from the luminance signal stored in the line memory 60 as described with reference to FIG.
Supply to. The system control circuit 72 creates a histogram and determines the above-mentioned HP and DP. When the mechanical section is ready for printing, the B signal is selected by the changeover switch 54. The selected B signal is digitized by the A / D converter 56, and B data for one row is written in the line memory 60 via the memory control circuit 58.

The data in the line memory 60 is sequentially read out, and the gradation conversion R is performed via the data ROM control circuit 62.
Applied to OM64. A 16-bit address composed of 4-bit HP, 4-bit DP, and 8-bit data from the line memory 60 is applied to the gradation conversion ROM 64, and the data after gradation conversion is read from the corresponding address. ..

The gradation-converted data is pulse-width modulated by the pulse-width conversion ROM 66 and applied to the head 70 via the head driver 68. In the sublimation thermal transfer system, the temperature of the head cannot be kept constant unless the applied pulse time is changed according to the current temperature of the head. Therefore, the system control circuit 72 detects the current temperature of the head 70 and converts the head temperature data into a pulse width conversion ROM.
66 is applied. In this way, yellow printing is performed.

When all lines of yellow have been printed, next, magenta is similarly printed by the G signal, and then cyan is printed by the R signal. In this way, printing of all colors is completed.

The outputs of the D / A converters 48 and 50 are applied to the color difference synthesizing circuit 74 to become chroma signals. The video encoder 76 forms a composite video signal from the output of the D / A converter 46 and the chroma signal output from the color difference synthesis circuit 74. Further, the luminance signal output from the D / A converter 46 and the chroma signal output from the chromaticity synthesis circuit 74 are output as a luminance / color difference separation type video signal. These are applied to, for example, a monitor and used for observing a printed image. Whether the input image itself is output as a monitor or the images stored in the memories 40, 42 and 44 are output as a monitor can be controlled by a command to the memory control circuit 38.

Next, the characteristic operation in the case of 4-screen printing will be described. In this case, from the Y data stored in the line memory 60, as described with reference to FIG. 6, the system control circuit 72 calculates HP and DP by a histogram for each of the four individual images and stores them, and B , G, and R are printed, the HP and DP addresses applied to the orthogonal transformation ROM 64 are switched at the switching positions of the individual images.

Further, in the case of 25-screen printing, as described with reference to FIG.
According to the maximum value and the minimum value of the brightness data stored in the memory 60, it is stored as HP and DP of each individual image. Then, as in the case of four-screen printing, the HP and DP addresses applied to the orthogonal transformation ROM 64 are switched at the switching position of the individual image when printing B, G, and R.

[0038]

As can be easily understood from the above description, according to the present invention, since the gradation conversion is performed by the highlight point and the dark point for each individual image of multi-image printing, each individual image is converted. You can print with good quality.
Further, even in multi-image printing of a large number of images such as 25 screens, the printing time does not become long.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a sampling range for creating a histogram for one-screen printing.

FIG. 3 is an example of a histogram.

FIG. 4 is a characteristic diagram of gradation conversion.

FIG. 5 is an explanatory diagram of multi-image printing.

FIG. 6 is an explanatory diagram of a histogram creation sampling range for multi-image printing of four screens.

FIG. 7 is an explanatory diagram of a histogram creation sampling range for 25-screen multi-image printing.

FIG. 8 is a circuit example of an LPF 26.

[Explanation of symbols]

20: Video decoder 22, 24: Changeover switch 26: LPF 28: Changeover switch 30: Color difference conversion circuit 32, 34, 36: A / D converter 38: Memory control circuit 40: Y memory 42: RY memory 4
4: BY memory 46, 48, 50: D / A converter 52: RGB matrix circuit 54: Changeover switch 56: A / D converter 58: Memory control circuit 60: Line memory 6
2: data ROM control circuit 64: gradation conversion ROM 6
6: Pulse width conversion ROM 68: Head driver 7
0: Head 72: System control circuit 74: Color difference synthesis circuit 76: Video encoder 80: LPF 8
2: Delay line 84: Adder circuit 86: Divider

Claims (3)

[Claims] 1. A video printer for printing a multi-image composed of a plurality of individual images, comprising: calculating means for calculating a highlight point and a dark point of the individual image; and a calculated highlight for each individual image. A video printer provided with gradation conversion means for converting the gradation of an individual image according to points and dark points. 2. The video printer according to claim 1, wherein the calculation means calculates the highlight point and the dark point from the histogram of the brightness of the individual image. 3. The video printer according to claim 1, wherein the calculating means sets the maximum value and the minimum value of the brightness of the individual image as a highlight point and a dark point, respectively.