JPH10108021A - Printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable conducting proper gradation expression, even when undesired high luminance points exist in image data to be printed out in the printer where printing accompanied with gradation expression is available. SOLUTION: A luminance signal Y is fed to a histogram detection block 30. In the block 30, a histogram for each gradation of the luminance signal Y is detected. In an accumulation/comparison block 31, the frequency of the level of the luminance is accumulated in this histogram. The cumulative frequency is compared with a prescribed threshold level, and the gradation in excess of the threshold level is used for a gradation of a highest luminance for printing. Moreover, in the case that the gradation reaches a prescribed limit before the cumulative frequency reaches the threshold level, the gradation is used for the gradation for the highest luminance. The luminance signal Y is corrected, based on the gradation at the highest luminance, and a YUV signal is converted into a YMC signal, based on the corrected luminance signal Y'. Since the highest gradation is decided based on the cumulative frequency of the luminance, a proper gradation representation is conducted, regardless of the existence of unwanted high luminance points.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a printer device which performs appropriate gradation expression by limiting the maximum value of luminance.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for a video printer which captures image data from a video image, a computer graphic, a digital still camera or the like, and performs high-resolution printing in color. For such applications, a sublimation-type thermal transfer printer is often used because of high image quality and no need for maintenance. In some cases, a printer based on a fusion-type thermal transfer system is used.

In a sublimation type thermal transfer printer, heat is applied to an ink sheet containing a sublimable dye as a main component, and the vaporized ink reacts with a polyester coating (called a precoat layer) on printing paper. Let it develop color. In order to apply heat to the ink sheet, for example, a thermal head is used. In this method, it is possible to express gradation in dot units by adjusting the amount of heat to be applied. For example, when 256 gradations can be output for each color of C (cyan), M (magenta), and Y (yellow), these colors are sequentially superimposed and printed to obtain about 1670
So-called full-color printing of all colors is possible.

[0004]

By the way, in such a video printer, the gradation level of the fetched image data is set to AGC (Aut) in order to express the gradation at the time of printing.
o It is necessary to make it constant by using a Gain Controller). In a conventional printer device, this level stabilization process is performed by detecting a peak value and an average value of a luminance value represented by image data and comparing these values with corresponding reference values. Was.

For example, the captured image data is subjected to peak detection by a peak detection circuit and a peak value is detected, and an average value is detected by an average value detection circuit. After a predetermined weight is given to each of these detected values, these values are added, and the added value is supplied to an amplifier having a variable gain. Then, in this amplifier, the supplied value is compared with a predetermined reference value, and based on the comparison result, the gain of the amplifier is controlled, and the level is made constant.

In this method based on the prior art, the detection circuits for peak detection and average value detection each have a predetermined time constant. Therefore, for example, if unnecessary high-luminance points based on noise, reflected light, and the like exist in the image data, the detected peak value and average value are affected by the high-luminance points. Therefore, the gradation level at the time of printing is not appropriately controlled, and at the time of printing, there is a problem that the entire image is darkened, and that a subtle high-brightness gradation cannot be expressed. .

In actual image data, the conventional AGC based on peak detection and average value detection needs to correspond to, for example, light from a reflector, cloud or snow surface, and light from a spotlight. There was a problem that was difficult.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a printer device capable of performing appropriate gradation expression even when unnecessary high luminance points exist in image data for printing. .

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a printer device capable of printing with gradation expression, a histogram detecting means for detecting a histogram for the luminance of a luminance signal, Accumulating means for accumulating the frequency from the high luminance portion of the histogram, comparing means for comparing the accumulated frequency with a predetermined threshold value, and maximum luminance for outputting the maximum luminance value at the time of printing based on the comparison result A printer device comprising: value output means; and conversion means for converting a luminance signal into a level corresponding to a maximum luminance value.

As described above, the present invention detects a histogram for luminance, accumulates frequencies from a portion having a high luminance in the histogram, and compares the accumulated frequency with a predetermined threshold. Since the highest luminance value at the time of printing is obtained, an appropriate gradation display can be performed according to the area of the high luminance portion of the image to be printed.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the configuration of a printer device to which the present invention can be applied. This printer device is, for example, one of video signals according to the NTSC system.
The frame is captured, and printing is performed in full color on predetermined paper by a sublimation thermal transfer method.

The printer apparatus applicable to the present invention is not limited to a sublimation type thermal transfer type. That is, the present invention can be applied to other types of printer devices capable of gradation expression.

An analog composite video signal is supplied to a television monitor (not shown) and to an input terminal 1 of the printer. The supplied signal is converted by the decoder 2 into a component signal composed of a luminance signal Y and color difference signals U and V. This component signal (hereinafter, referred to as a YUV signal)
Are converted into digital signals by the A / D converter 3 and supplied to the frame memory 4.

On the other hand, the user can specify a scene to be printed by the printer device while viewing the video signal displayed on the monitor. When the scene to be printed is displayed, the user presses a memory capture switch (not shown). When the memory capture switch is pressed, one frame of the digital video signal output from the A / D converter 3 is written into the frame memory 4 at the video rate during the scanning period under the control of the memory controller 5.

Although not shown, the supply of the video signal to the above-mentioned television monitor is connected to an output terminal 8 to be described later, for example, via a switch circuit which is selected according to the memory fetch switch. You. With this configuration, a video signal can be supplied from the output terminal 8 to the above-described television monitor when the memory capture switch is pressed.

That is, after the memory fetch switch is pressed and a video signal is written to the frame memory 4, the video signal written from the frame memory 4 is read at a video rate. The read video signal is supplied to the D / A converter 6 and converted into an analog component signal. The output of the D / A converter 6 is supplied to an encoder 7, converted into, for example, a composite video signal suitable for display on a monitor, and led to an output terminal 8. Then, the derived video signal is displayed on a monitor connected to the output terminal 8.
The user can confirm the print image by looking at the display on the monitor.

The digital video signal written in the memory 4 can be subjected to predetermined image processing based on, for example, an instruction from a user. For example, the user operates a switch (not shown) or the like, and instructs the CPU 20 to perform image processing.
Based on this instruction, video data is read from the frame memory 4 by the CPU 20 and written into, for example, a RAM (not shown). This RAM is used by the CPU 20.
Is subjected to predetermined image processing, and the image-processed video signal is written to the frame memory 4 again.

After these processes, the printing process is started when the user presses a printing button (not shown). When the printing process is started, a video signal for one frame is read from the frame memory 4, and
It is supplied to the YUV / YMC conversion circuit 10. YUV / Y
The MC conversion circuit 10 detects a histogram of each gradation value for the luminance signal Y in the video signal. Then, a tone value corresponding to 100% white is obtained based on the histogram.

When the histogram is detected and the luminance level Y 'is obtained, the video signal for one frame is read out again from the frame memory 4, and the circuit 10 extracts the video signal from the signal composed of the luminance Y and the color difference U and V of the video signal. Y (Yellow),
Conversion into signals of respective colors of M (Magenta) and C (Cyan) (hereinafter, referred to as YMC signals) is performed. At the time of this conversion, the white 10 obtained based on the detected histogram is used.
Based on the gradation value equivalent to 0%, gradation compensation is performed on the video signal. These YUV / YMC conversion circuits 10
The details of the processing in will be described later.

The video signal thus tone-corrected and converted into signals of each of the YMC colors is subjected to tone correction, contour correction, etc. in the γ correction circuit 11 and the aperture correction circuit 12, respectively. Are converted into gradation data, supplied to the print head 14, and printed on a predetermined sheet. The printing head 14 is controlled by the number-of-currents temperature compensating unit 13 to perform printing stably, so that optimum printing can always be performed. Printing is performed for each color sequentially. At the time of printing, control such as paper feeding is performed by the CPU 20.
Is performed by the motor driver 23 which is controlled as follows.

During printing, control is performed so that new video data is not written to the frame memory 4. On the other hand, the frame memory 4
Thereafter, since the video signal is read out at the video rate based on the scanning period during this period, the television monitor connected to the output terminal 8 displays the scene selected by the user for printing. Is displayed.

Next, the above-mentioned YUV / YMC conversion circuit 1
The gradation compensation at 0 will be described. Figure 2 shows the YUV
/ YMC conversion circuit 10 and its circuit 1
0 schematically illustrates the processing performed at 0. As shown in FIG. 2C, the YUV / YMC conversion circuit 10 includes a histogram detection block 30, an accumulation / comparison block 31, and a YUV / YMC conversion block 32. Accumulation/
The comparison block 31 includes a limiter circuit.

The digital video signal supplied to the circuit 10 includes a luminance signal Y and a color difference signal U, as described above.
V. Among these, the luminance signal Y is the histogram detection block 30 and the YUV / YMC conversion block 3
2 are supplied. The color difference signals U and V are YUV / Y
It is supplied to the MC conversion block 32.

In the histogram detection block 30,
The frequency of each gradation is obtained by accumulating the supplied luminance signal Y for each gradation in pixel units, and a histogram for the gradation of the luminance signal Y is detected. FIG. 3 shows an example of the configuration of the histogram detection block 30. The histogram detection block 30 has a memory 40 having a size of 256 words in units of one word composed of, for example, 16 bits. In this memory 40, an address is provided for each word.

[0] to [255] are assigned. These address values directly represent gradation values corresponding to the respective addresses.

When the luminance signal Y is supplied, first, the contents of the memory 40 are erased. Since the luminance signal Y is written in the frame memory 4 as a digital video signal, for example,

It has a value of [0] to [255]. When the luminance signal Y read from the memory 4 is supplied to the histogram detection block, the memory 40 is accessed using the data value of the signal Y as an address value, and the value written at the corresponding address is read. Then, “1” is added to the read value by the adder 41. The added value is written to the same address of the memory 40 again. As a result, the number of pixels at each gradation is accumulated for the luminance signal Y, and a histogram for the gradation of the luminance signal Y is detected as shown in FIG. 2A.

Next, in the accumulation / comparison block 31,
The number of pixels of each gradation detected by the histogram detection block 30 (that is, the frequency for each gradation) is cumulatively added from the portion having the highest luminance. That is, as shown in FIG. 2B, in the histogram, from the portion where the number of pixels of each gradation is high in luminance, x ₁ + x ₂ + x ₃ +... + X _n + x
_{n + 1} ... is cumulatively added. Then, when the cumulative number of pixels obtained by the cumulative addition exceeds a preset threshold value TH, the tone at the point when the cumulative pixel number exceeds the threshold value TH is set to the highest luminance in printing, that is, a level corresponding to 100% white. You.
In the example shown in FIG. 2B, x ₁ + x ₂ <TH, and
In addition, since x ₁ + x ₂ + x ₃ ≧ TH, the luminance level of the third gradation from the gradation having the highest luminance is the white 10 at the time of printing.
This is a level equivalent to 0%.

In the above description, when calculating the cumulative number of pixels, it has been described that the number of pixels of each gradation is accumulated from a portion having a high luminance. However, this is not limited to this example. For example, the number of pixels can be accumulated from a portion having a low luminance. Since the total number of accumulation is determined by the number of pixels of the video signal written in the frame memory 4, similar results can be obtained by sequentially subtracting the accumulation value from this total number.

In the above description, when detecting a histogram, accumulation is performed for all pixels for one frame. However, this is not limited to this example. That is, the histogram may be detected by extracting only the representative points from the pixels for one frame. This is achieved by, for example, thinning out pixels of one frame at predetermined intervals, such as every other pixel.

The accumulation / comparison block 31 includes:
When the number of grayscale pixels in a high-luminance portion is small, white 10
A limiter is provided for limiting the level corresponding to 0% to a predetermined gradation. In this limiter, a predetermined gradation is set in advance as a limit value LIMIT. As shown in FIG. 4, when the above-described gradation in which the number of accumulated pixels exceeds the preset threshold value TH is lower than the gradation set as the limit value LIMIT, the floor indicated by the limit value LIMIT is used. The brightness level of the tone is a level corresponding to 100% white.

As described above, when a level equivalent to 100% of white is obtained by the threshold value TH or the limit value LIMIT,
The range shown in FIG.

From [0], the gradation at the time when the accumulated pixel number exceeds the threshold value TH, or the gradation

Printing is performed from [0] with the gradation range indicated by the limit value LIMIT as the effective range of the luminance signal Y. That is, when the gray level corresponding to 100% white obtained by the threshold value TH or the limit value LIMIT is WY, the level Y ′ of the luminance signal Y ′ based on the gray level WY is the level of the original luminance signal Y. From Y, it is obtained by the following equation (1). The operation performed on each pixel at the time of printing is performed based on the level Y ′ obtained by the equation (1).

Y ′ = Y × (255 / WY) Expression (1)

As shown in FIG. 5, weighting may be performed for each gradation. In the example shown in FIG. 4 described above, the number of pixels of each gradation is cumulatively added as it is. On the other hand, in the example shown in FIG. 5, the number of pixels of each gradation is multiplied by a predetermined coefficient and cumulative addition is performed. Also in this case, the setting of the threshold value TH and the limit value LIMIT is performed in the same manner as in the example shown in FIG. In this manner, by performing weighting on the gray scale and performing cumulative addition of the number of pixels, it is possible to increase the accuracy in determining a threshold value for a predetermined gray scale.

In the equation (1), when the value of Y 'exceeds [255], the luminance value of the pixel is set to [255].

FIG. 6 shows the accumulation / comparison block 31 described above.
An example of the configuration will be shown. The memory 40 in which the histogram composed of the number of pixels of each gradation is written is shared by the above-described histogram detection block 30 and the accumulation / comparison block 31. Here, these memories 40 and 5
2 is different from the memory 40, but this is for convenience of explanation.
And 52 consist of one memory. The memory 52
Like the memory 40, it has an address corresponding to each gradation,
This is a table in which coefficients at the time of weighting for each gradation described above are written in advance at corresponding addresses.

In the switch circuit 57, the limiter 58 is initially selected. This switch circuit 57
For example, selection is controlled based on a supplied trigger signal.

For example, a system clock CLK in the printer is supplied to an address generation circuit 50.
In address generation circuit 50, an address signal for designating addresses for memories 40 and 52 is generated based on this clock CLK. This address signal is for memories 40 and 52,
And 52, and a latch circuit 5 described later.
1 is supplied. Reading of data from the memories 40 and 52 is performed while sequentially decrementing the address value from the address corresponding to the higher-luminance gradation based on the address signal specifying the address for the same gradation.

The data read out from the memories 40 and 52 in this manner, that is, the number of pixels of a predetermined gradation and the weighting coefficient are supplied to the multiplier 53, respectively. The multiplier 53 performs a weighting operation on the number of pixels of the gradation, and the obtained result is supplied to one input terminal of the adder 54. The output of the adder 54 is written to the register 55. The data read from the register 55 is supplied to the other input terminal of the adder 54. In this manner, the output of the adder 54 is sequentially supplied to the other input terminal of the adder 54, and is added to the output of the multiplier 53, so that the above-described cumulative number of pixels can be sequentially obtained.

This accumulated number of pixels is supplied to one input terminal of the comparator 56. A predetermined threshold value TH is supplied to the other input terminal of the comparator 56, and the accumulated pixel number is compared with the threshold value TH. As a result of this comparison,
When the cumulative number of pixels ≧ the threshold value TH, the comparator 5
From 6, a predetermined trigger signal, for example, a pulse signal is output. The trigger signal is supplied to the switch circuit 57 as a control signal and is also supplied to the latch circuit 51 as a latch signal.

As described above, the address signal is supplied from the address generation circuit 50 to the latch circuit 51. This address signal is latched by the latch signal supplied from the comparator 56. At the same time, the switch circuit 57 switches the selection from the limiter 58 side to the latch circuit 51 side by the latch signal. Therefore, the address signal latched by latch circuit 51 is output from accumulation / comparison block 31 via switch circuit 57. As described above, the address signal directly represents the gradation value, so that the output of the address signal is the gradation W corresponding to 100% white.
Y is set.

In the switch circuit 57, as described above, the limiter 58 is selected in the initial state. This limiter 58 has a preset limit value LIM.
When the access to the memories 40 and 52 reaches the address corresponding to the limit value LIMIT and the cumulative number of pixels ≧ the threshold value TH does not hold, this limit is output via the switch circuit 57. Value LIMIT is white 1
It is output as a gradation WY equivalent to 00%.

Although the above description has been made on the assumption that the address signal directly represents the gradation value, the present invention is not limited to this example. For example, even if the address signal indicates an address specific to the memories 40 and 52, the latch circuit 51
A similar effect can be obtained by providing a conversion table between the switch and the switch circuit 57 and converting the address signal into a corresponding gradation value.

The tone WY equivalent to 100% white thus obtained is supplied to the YUV / YMC conversion block 32. In this block 32, a signal consisting of a luminance signal Y and color difference signals U and V is converted into a Y (Yel
low), M (Magenta), and C (Cyan). This conversion is performed by calculating the above-described equation (1) for each pixel, and calculating the following equations using the obtained Y ′.

Y = Y '+ V

M = Y ′ + (− 0.51) × V + (− 0.19) × U

C = Y '+ U5

The Y, M, and C color signals obtained by the conversion by the YUV / YMC conversion block 32 are
The signal is output from the / YMC conversion circuit 10 and supplied to the subsequent stage γ correction circuit 11, aperture control circuit 12, etc., and is subjected to signal processing necessary for printing and printed.

FIG. 7 shows a comparison between this embodiment and the 100% white level in the conventional method. In this figure, the vertical axis indicates the level of the luminance signal Y, and the horizontal axis indicates the horizontal line position. As shown in FIG. 7A, in the luminance signal Y, when a signal having a very narrow width but an extremely large level, such as noise, is present, the conventional method of performing AGC based on a peak has the extremes. The highest level is the level of 100% white, resulting in an overall dark and sunk print.

On the other hand, in the method according to the present invention,
100% white based on the histogram due to the cumulative number of pixels
Determine the level. Therefore, as shown in FIG. 7B, when the number of pixels of the peak is large, the level of 100% white is determined based on this peak, but when the width of the peak is small as in the example shown in FIG. 7A. The effect of this peak on the whole is small, and the level Y 'is white 1
00% level.

In this embodiment, a means for detecting a histogram pattern is separately provided, and the value of the threshold value TH is changed according to the histogram pattern. Can do it.

[0050]

As described above, according to the present invention, a histogram of luminance values of an input video signal is created, and values accumulated in order of luminance are compared with a predetermined threshold value based on the histogram. The luminance at the time when the threshold value is exceeded is set as the maximum luminance when printing. for that reason,
It is possible to detect the highest luminance in the print data according to the area of the high-luminance part of the printing screen. Thus, there is an effect that printing can be performed.

Further, according to the present invention, by weighting each gradation, the compensation of the highest luminance can be limited to a specific range, and there is an effect that over-compensation can be prevented.

Further, according to the present invention, by changing the value of the threshold value TH according to the pattern of the histogram, there is an effect that printing can be performed with an intentional expression.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a configuration of a printer device to which the present invention can be applied.

FIG. 2 is a block diagram illustrating an example of a configuration of a YUV / YMC conversion circuit, and a diagram schematically illustrating processing performed in the circuit.

FIG. 3 is a schematic diagram illustrating an example of a configuration of a histogram detection block.

FIG. 4 is a diagram schematically illustrating a method of determining a level corresponding to 100% white using a histogram.

FIG. 5 is a diagram schematically showing a method for determining a level corresponding to 100% white using a histogram.

FIG. 6 is a schematic diagram illustrating an example of a configuration of an accumulation / comparison block.

FIG. 7 is a diagram showing a comparison between the embodiment of the present invention and the level of 100% white in the conventional method.

[Explanation of symbols]

10 YUV / YMC conversion circuit 30 Histogram detection block 31 Cumulative / comparison block
32 ... YUV / YMC conversion block, 40 ... memory, 50 ... address generation circuit, 51 ... latch circuit, 52 ... memory, 56 ... comparator

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazumasa Miyazaki 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Toshiyuki Iijima 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo No. Sony Corporation

Claims (3)

[Claims] 1. A printer device capable of performing printing with gradation expression, a histogram detecting means for detecting a histogram for the luminance of a luminance signal, and an accumulating means for accumulating frequencies in a direction of change in the luminance of the histogram. Comparing means for comparing the accumulated frequency with a predetermined threshold value; maximum luminance value output means for outputting a maximum luminance value at the time of printing based on the comparison result; and transmitting the luminance signal to the maximum luminance value. And a converting means for converting the level into a level corresponding to the level. 2. The printer device according to claim 1, wherein the maximum brightness value output means sets a predetermined limit value as the maximum brightness value when the accumulated frequency does not reach the predetermined threshold value. A printer device for outputting. 3. The printer device according to claim 1, wherein said comparing means performs said comparison by weighting said frequencies by predetermined weights.