JPS6297482A - Video printer - Google Patents

Abstract

PURPOSE:To correct a shortage in contrast of an input image and to obtain a clear printed image by deciding the degree of the contrast of the input image from the frequency distribution classified by density of the input image, and correcting the frequency distribution classified by density. CONSTITUTION:A video signal inputted from an input terminal 1 is stored at a frame memory means 5 as a digital luminance signal and a color difference signal through a color difference conversion means 2, an LPF3, and an A/D converter 4. Out of stored bits of image information, a signal Y is inputted to a signal correction means 6, and a correction factor is calculated. And again a bit of signal Y information is read out from a frame memory 501, and after it receives a correction conversion so as to set the contrast at an appropriate level with an obtained correction factor, it is stored again at a frame memory 7. The bit of signal Y information, the contrast of which is corrected, at the frame memory 7 is read out with the bit of color difference signal information at frame memories 502 and 503, then being sent to a D/A converter 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a video printer suitable for printing an image based on a received video signal or a video signal from a video camera.

[Background of the invention]

Conventionally, as disclosed in Japanese Patent Application Laid-Open No. 56-648114, there have been known video printers that print images faithfully to input video signals and video printers that can adjust the γ characteristics of prints. A brightness adjustment means is provided that uniformly changes the brightness of the entire image to achieve a desired brightness.

However, in these conventional techniques, the overall brightness is changed uniformly, so if an image with insufficient contrast is input, even if the brightness of the print image can be adjusted, the resulting print The problem was that the image still lacked contrast, making it impossible to obtain a clear printed image.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a video printer that solves the problems of the prior art described above and can appropriately correct the lack of contrast in an input image to obtain clear printed images.

[Summary of the invention]

In order to achieve this objective, the present invention obtains a density frequency distribution of an input image from data representing the density of each pixel in the input image, and determines the degree of contrast of the input image from the frequency distribution by density. However, the present invention is characterized in that the density-based frequency distribution of the input image is corrected so as to enhance the contrast, thereby obtaining a print image with optimum contrast.

[Embodiments of the invention]

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

FIG. 1 is a block diagram showing an embodiment of a video printer according to the present invention, in which 1 is a video signal input terminal, 2 is a color difference conversion means, 3 is a low-pass filter (hereinafter referred to as LPF), and 4 is an analog/ Digital conversion means (hereinafter referred to as A
/D conversion means), 5 is a frame memory means, 50
1 to 503 are frame memories, 6 is a signal correction means, and 60
] is a data classification means, 602 is a concentration-based counting means, 60
3 is a density correction judgment means, 604 is a variable coefficient means, 7 is a frame memory, and 8 is a digital/anacog conversion means (
(hereinafter referred to as D/A conversion means), 801 to 803 D
/A converter, 9 is RG B conversion means, IO is signal selector, 11 is A/D conversion means, 12 is line memory, 13 is halftone control means, 14 is thermal head, 15 is encoder for monitor , 16 is a memory controller, 1
7 is a print controller, and 18 is a signal correction controller.

In the figure, the A/D conversion means 4 is composed of three A/D converters for one luminance (Y) signal and one color difference (RY, BY) signal. Similarly, frame memory means 5. D
/A conversion means 8 also have three frame memories 5 each.
01,502,503 and A/D converters 801, 80
2.803. Further, the signal correction means 6 includes data classification means 601. Concentration-specific counting means 602. Density correction determining means 603. It is composed of variable coefficient means 604.

Next, the operation of this embodiment will be explained.

First, the video signal input from the input terminal (in this case, this video signal is an N
It is a TSC type signal. ) are converted into luminance signal Y, color difference signal (RY'), (B-Y) by color difference conversion means 2.
is converted into Of course, when a monochrome video signal is input, only the Y signal is obtained, but the following operation is also applicable in this case. These signals are each limited to a predetermined band by the LPF 3 at the next stage. For example, L.P.
The cutoff frequency of F3 is approximately 4.
5M)Iz, (R-Y), (13-Y) signals are selected to be approximately 0.5MHz. Then, these signals are converted by the A/D conversion means 4 to 6 to 8 MHz, respectively.
The information is converted into bit digital information and stored in each frame memory 501, 502) 4 of the frame memory means 5 at the next stage.
03.

The video image information stored at this time is stored in the respective memories 501 and 50 according to the memory controller 16, which operates in response to a freeze command from the print controller 17 (a command to store the image to be stored in the frame memory).
2,503. The image information stored in the frame memory means 5 is only the part that is effective for printing.
The amount of information is, for example, in the vertical direction, the number of effective scanning lines N
v is only 480 to 485 lines, and in the horizontal direction, it is about 48 μsec in a - period (63.5 μSθC). Although this 48 μsec is an example, this value is obtained when sampling NH=512 times in the horizontal direction at a frequency three times that of the color subcarriers f, e (=3.58 MHz), and therefore 512/3. It can be found from fsc.

Among the image information recorded in the frame memory means 5,
Only the Y signal information is read out from the frame memory 501 and input to the signal correction means 6 at the next stage.

Here, as will be described later, a correction coefficient is calculated from this Y signal information. Then, the Y signal 1a information is read out from the frame memory 501 again, subjected to correction conversion using the obtained correction coefficient so that the contrast becomes appropriate, and then stored in the frame memory 7 again. The correction conversion timing and the like at this time are controlled by the signal correction controller 18. The contrast-corrected Y signal 1n information of the frame memory 7 is sent to the (R
-Y), (f3-Y) are read together with the signal information, and D
The data is converted into analog information by the D/A converters 801 to 803 of the /A converting means 8, and then sent to the next stage RGB converting means 9.
The signal is converted into primary color signals of red (R), green (G), and blue (B). Along with this, analog Y, (RY).

After the (B-Y) signal is processed by the encoder 15,
The signal is supplied to a monitor (not shown). This allows you to check the corrected image information on the monitor.

Here, in this embodiment, a color image is printed using a three-color plane sequential method in which three colors are sequentially printed one screen at a time. For this purpose, the signal selector 10 controlled by the print controller 17 receives the R,
One type of G and B signals is selected in turn for each screen.

In the case of a three-color line sequential method in which three colors are printed one line at a time, the signal selector 10 selects R, G, [3 color numbers as 1].
It is sufficient to select one type for each line in order.

The primary color signals selected by the signal selector 10 are converted into digital information by the A/D conversion means 11, and then stored in the line memory 2 in an amount necessary for printing one line. Then, the digital information read from the line memory 12 is converted by the halftone control means 13 into a parameter that can control the density, for example, a pulse width that determines the printing time, and then is applied to the thermal spatula F14 to be printed. Ru. The position of the line to be printed, the printing timing, etc. at this time are all controlled by the print controller 17.

Next, the operation of the signal correction means 6 will be explained with reference to FIGS. 2 and 3. The main operations of the signal correction means 6 are: 1. Obtaining the density distribution of the memorized Y signal information; 1. Decide a pattern to be corrected from 1. Calculate its correction coefficient to correct and convert the input information; 2. Store the converted data in the frame memory 7 again according to the address.

First, (1) Calculation of concentration distribution is performed as follows.

The Y signal information read from the frame memory 501 is supplied to the data classification means 601, and each pixel data is classified into each density gradation. In other words, when each pixel is 6-bit data, there are 64 gradations, and when each pixel is 8-bit data, there are 25
Classified into 6 gradations. As the data classification means 601, a general data comparison means or a data decoder is sufficient.

The results obtained by classifying in this way are supplied to the density-based counting means 602 at the next stage, and the number of pixels for each gradation is counted. Now, if each image data is n bits, there are 2" types Ta of density gradation O~<2n-1).The number of "-" counts at each density gradation is N, (i=0~2") -1)
When the number of valid sample scanning lines in the vertical direction is Nv and the number of valid samples in the horizontal direction is N□, the following relationship holds true.

Now, to simplify the explanation, it is assumed that n=4 and the distribution of the count number N of each density gradation is as shown in FIG. 2, for example. In the figure, the horizontal axis represents the concentration, and the vertical axis represents the count number N1.

Suppose that is white and density D15 represents black. Second
Figure f8+ is a histogram when the input image has weak contrast and is entirely dark, and Figures 1 and 2 (
bl is a histogram for an overall bright image with no contrast.

In this way, the density distribution of the Y signal information of (2) above is obtained.

Next, the correction pattern (2) is determined by the density correction determining means 603 as follows.

However, 7711 shown in Fig. 2 obtained from the input image
The degree distribution has its maximum density D IIAX 7J<D 15 and its minimum density. 1. Gari. A correction pattern is determined to convert the density distribution into an overall extended density distribution so that

Now, let L)8 be any depth that the input image has, let C1'M be the corrected density distribution, and let C1'M be the minimum density.
Assuming that AX+D's+,l, a correction pattern is determined so that this density is corrected to the density D' by the following equation (2).

[)'l-1 (D'MAX-D'*to 1) (D・--
D4ts)・′(1,)□x D14+++)
+DM+q +0.51...(2) Here, the symbol (X) on the right side of +21 above is a Gauss symbol that takes only the integer part of X, and +0.5 in formula I2) is a correction for rounding. be. , i:, When the concentration distribution in Figure 2 (a), peak) is corrected using equation (2), at n -4, D
'□X=15. D'MI+1=O,T)14AX
”13. Since DMIN-6, Figure 3 (al
, it becomes (bl's yo). In other words, there is a lot of contrast. The image is corrected to spread over a wide range from (white) to I) +5 (black).

In the above explanation, D□8. D□3 each. 1
Although the concentration is expanded to the maximum up to Dl, it is not necessarily limited to this, and the maximum and minimum concentration after capture D'5 +
D) lIy, [)') IAx −(1−α) D+s
...(3) D'M + 41- αD,,,
...As for (4), it's a little bit restrained 6.
It is okay to have two offshores.

In addition, as the correction coefficient for the above-mentioned ■, (2
"1) / (DMAX DMIN) or formula (3).

It can be considered as α in (4). Furthermore, the above
The information stored in the frame memory 7 is controlled by the signal correction controller 18.

As shown in Figure 2, the above signal correction operation is effective for input images without black and white levels (D, , D, r,), but as shown in Figure 4, when these black and white levels It has no effect on input images with density distributions that include . This is DMA
X-2' 1. This is because, since D, 4+do〇, D+=[)'+ in equation (2), and no correction is performed. For such a density distribution, the contrast can be corrected as follows.

The characteristics of the density distribution shown in Figure 4 are that pure white (D) and pure black (
])l, ) also have a small portion, but there is no contrast throughout, resulting in a dark image input. In such a concentration distribution state, first, lower and older threshold concentrations 1), DH, expressed by the following equations, are determined.

D,, =I)x D Further, the symbol MIN(f) on the right side represents the minimum value of the parameters x and y that satisfy the conditional expression f.

The concentration DI- in equation (5) is the concentration DI- in FIG. The number of counts N, is accumulated sequentially from the side. From 'L1 degree I-)16 in Figure 4, force lie 1 number N.

is the minimum concentration at which the cumulative value is greater than or equal to the cumulative value.

With this correction method, all densities below 191 are densified.

All concentrations exceeding the concentration LlH are the maximum concentration D1. At the same time, the above correction is performed so that the density in the range of D+, ``DH is expanded to the range of Ia, ~D14. Therefore, the correction formula at this time is obtained from the above equation (2). , D'MAM = 2" 2 [)'M
IN=1DHAM=DHI), 4+w=DL
Therefore, D'yu = c <2'''-3)(
1) + -or, > / (DHDL)
+1.5 J... (l).

From this, when β≧0.5, DL zDH becomes true, and correction becomes impossible.

Therefore, when β-0,2 is applied to the concentration distribution in Fig. 4, Dl. -Dy, DH=Dis, and the correction target data is limited to 1) 7 to D, :l. At this time, a low concentration of tIi occurs. -D6 are all compressed to D'o, and similarly I) Ia, D + s are compressed to D'1.
Compress it into When D and ~Dl+ are corrected using Equation 6 (7), the obtained concentration distribution becomes as shown in FIG.

In addition, the density in FIG. 5-C2 in FIG. 4.

and Dl or density r], and 4 and Dis are adjacent to each other, which looks unnatural, but the actual number of gradations is extremely large, 64 or 256, as mentioned above, so this is not a problem at all. .

Note that the coefficient β is the 1 degree distribution of the input image 15i! The decision should be made accordingly. For example, for an input image with a uniform frequency distribution, it is preferable to set β to a value close to 0, and for an input image with a biased frequency distribution, it is preferable to set β to a relatively large value. The determination of the contrast coefficient β can be done manually by monitoring the input image to be printed,
Alternatively, this can be done automatically by determining what state the frequency distribution is in using an appropriate means such as a microcombi controller.

The embodiments described above are sufficiently effective for general input images. However, the embodiment described in J-2 is insufficient for recommending an input image that is extremely lacking in contrast, especially in areas where the density frequency is high. This is because the above example expands the contrast uniformly, so even if the above correction is made in the area where the density frequency is high, the density frequency is still high, and the contrast in this area is slightly improved. This is because there is no need to worry.

For example, as shown in Figure 6, ? When the above equation (7) is applied to an input image with a degree distribution in which the portions with high store degrees are shifted toward the density DIS side, the frequency distribution obtained is as shown in Figure 7. Become.

As is clear from the figure, there is a contrast, but the part with high density frequency is also biased toward the 1G: [)'+ s side, and in this part, most of the 1' non I and last are modified -C Every time I'm gone.

FIG. 8 is a block diagram showing a signal correction means of another embodiment of the video printer according to the present invention which solves such problems, in which C1fi05 is a frequency averaging means, 606 is a coefficient selection means, GO7 and 608 are The input terminal and 609 are the output terminals, corresponding to Figure 1! The same reference numerals are given to the I parts.

This embodiment is similar to the embodiment shown in FIG. 1 except for the signal correction means 6, so only the signal correction means 6 will be described.

In FIG. 8, C, Y signal information read from the frame memory 501 (FIG. 1) is supplied from the input terminal 607 to the data classification means 601 and processed, and the obtained density data is sent to the density-specific counting means 602. is supplied to obtain the density frequency distribution for the input image.

This distribution information is subjected to the following calculation processing by the frequency averaging means 605 to obtain the average density DA and the average frequency N4.

1=01.O In this embodiment, the coefficient selection means 606 controlled by a control signal supplied from the signal correction controller 18 (FIG. 1) via an input terminal 608 obtains the coefficients obtained by such calculation. The frequency at each depth is equivalently averaged using the average concentration I)A and the average frequency NA, and thereby the following effects are to be obtained.

(],) Even in an image with a certain degree of contrast, the gradations in areas with high density frequencies are expanded and printed.

(2) Even if the highest temperature and lowest density exist, if they occur infrequently, the print will be compressed. In other words, the elongation of the intermediate density area is not hindered by slight high-density change areas or low-density change areas.

(3) Overall -) Since the density distribution is good, the non-trust balance is good and the image is easy to see.

Various methods can be considered for printing to average the wetness level to obtain the above effects, and examples thereof will be explained below. This means that in the density frequency distribution obtained from the input image, when frequencies are accumulated in order of density gradation, this cumulative value is the average frequency N
, l, the total density gradation is divided into groups, and these groups are sequentially assigned to new density gradations.

For this purpose, the following procedure is repeated.

(1)? P; AJJt Intermediate γ coral degree DI ((However, 1-(= (2'-' -0, 5)
, where [ ] represents an integer) and its average concentration DA
(i) If DA>DI+ (if the average concentration DA is on the "-" side than the intermediate temperature), perform the method in F (2).

(ii) D A < L) 4 cases of u, I),
A method similar to (2) below is performed from the n- side.

(2) Now, assuming that the density after correction is D', calculate 4 (k) from the following equation (10), and calculate the +74 (k-1)th 1) of the density frequency distribution obtained from the input image. The concentration of DItx-++. The 7th agricultural degree Jn++ from 1st to f(k)th is the above concentration.

By this equation (10), now the concentration D'o (k = 0)
When calculating the density D1 of the input image to be set, from equation (10), the density D1 is calculated. -DQ(Il+ is obtained, and this becomes the new density σ. Next, the density [■] of the input image to be made into the density σ1 (k=1.) is determined by the above equation (10). -D, (1) can be found, but the concentration of these. -Dago) is the concentration D'. Since the concentration D(1<o+., ~DIl, l+ is the concentration D
becomes ′+. In the same manner, each density of the input image is assigned to a new density σ5, and the density 1) 2'' -2
After allocating to the remaining concentration.

are all assigned to the density D'p''-+.

When such processing (2) is performed, β(
10-j! What phenomenon is (k-1)? ↓There is some confusion. Therefore, along with process (2), the next process (3) is performed.

Use (4) in A31.

In step (10), β(k) is obtained and a new density D' is determined. Depending on the V degree N' for this density Dy, which of the following processes (3) and Proceed to crab.

+3) If N'≦N8, then the next density D'. In order to determine 1, the process proceeds to step (2).

(4) If N-x>NA, i=0 (k 10a +1..5) X NA -(11
) and find the integer a. (A) If a=1, proceed to the above process (2) to set 41 as the next density [)'.

(B) If a is an integer of 2 or more, set N' to 1 to N'K...-+=0, and proceed to the above process (2) to determine [)'X 4 m.

The depth W degree is averaged as described above, but here, taking the 6th M temperature degree distribution as an example, and calculating the page degree distribution of the averaged density using specific numerical values, It will look like Figure 9.

In addition, the frequency of each electric power production in j→ in FIG. 6 was set as shown in Table 1 below.

A Table 1 Therefore, in this concentration frequency distribution, the above formula (8).

From (9), the average concentration DA+ and the average frequency NA are respectively DA
``''D-th ・NA=5, and the intermediate density DH is D++=Dq, so DA>DH.

Here, two to three examples of density D'1 in FIG. 9 will be determined. Note that the NA is 5 due to the above.

Concentration σ. For: In this case, k=o, and from Table 1 and equation (10), the densities D3 to D5 in FIG. 6 are therefore assigned to the density D'o. Concentration D'. frequency N'. are Tables 1 to 4. Therefore, in process (3), the process proceeds to process (2) to determine dark JK [)′+.

Density D', C: In this case, since k=l, the density 1), , D in FIG. 6 is assigned to the density D'+. ) The frequency N'+ of 'Agricultural degree'1 is 3 +
Since 4 = 7 and therefore greater than the average density NA, proceed to process (4). In this case, j! in equation (11) (k') is obtained as follows. Now, k=
1, therefore, use equation (10) to increase the value of k by 1 from 2, and find A (k) for each value. by this,
7! (k)≠I! (1) and 1 for the first k (
k) is 1 <i>. For concentration 0+, k
ll(k) when =2, Zunawaji, 7! (2) is 1
(x') becomes. So, from equation (10), we get J6 x (1,5+a)X5≦16<(2,5(-a)X)
5, and a=l.

Therefore, through process (4) (A), the process proceeds to process (2) in order to satisfy the next density σ2.

Concerning the density D': In this case, since k=3, although the explanation is omitted, the density Dz is assigned the density D6, and therefore the density Dx is assigned the tm degree Do, and its frequency N ', is 1 with frequency Nq = 1. Therefore, proceed to process +4j, but if p(k') is found in the same way as in the case of concentration DI, n (k') = 10
Then, (3,5+a)x5≦32〈(4,5+a) x 5
Therefore, a=・2. Therefore, (I3 of process (4)
) and set N4-0. Due to dirt, the next density D'
4, no density D1 is assigned and the frequency is zero. Then, the process proceeds to process (2) to determine the next density D'5.

When the density D'1 is determined in this manner, an averaged degree frequency distribution shown in FIG. 9 is obtained.

The above processing has a density of D A > D 11. However, in the case of DA<DI+, the above formula (10) is used and the same procedure is performed from the concentration D2n, , l side (for this reason, the obtained 6'(k) is A ( 2°-1k)), and the following equation (11') is used instead of equation (11).

The above method is one method for data averaging.
You may also do it from both sides at the same time. In this case,
Regardless of the relationship between the average density DA and the intermediate density DA, the above processes (2) to (4) may be repeatedly executed.

By further applying this embodiment to the correction frequency distribution subjected to the corrections from FIG. 4 to FIG. 5, it is possible to obtain a print image with even further enhanced contrast.

In the embodiments described above, it is possible to obtain a printed image by increasing the contrast of the input image, but the corrected density frequency distribution may have a gradation tA density where no density exists.

FIG. 10 is a diagram showing still another embodiment of the video printer according to the present invention which improves this.
] is correction type A/I) conversion means, 191 is ノ入/'
1) Converter, 192 is base 14! Voltage D/A converter, +
93 tJ base voltage voltage 11 data memory, 194 is a means for generating a constant voltage coefficient, and corresponds to Fig. 1 and Fig. 8. Explanation will be omitted.

In FIG. 10, input image information tq is recorded in the frame memory means 5, C, as in the case of FIG. Here, the moisture frequency distribution for the input image is shown in Figure 11fdl.
It shall be as follows. Gonouji Y signal's carefree, C is frame memory! ill, and the data classification J stage of the signal correction means 6 fi01. For example, the 6L eel 7 agricultural degree frequency 4j shown in FIG. The detection means 60'i calculates the difference ΔN between the average frequency NA and each concentration tr+degree N+ using the following equation (12), and obtains a correction coefficient as shown in FIG. 11(b).

ΔNi =-N,,-Ni...(
12) Further, in the next stage reference voltage coefficient generating means 194, a ramp function (a proportionally increasing function) M is applied to this ΔN8.
(i) = NA - i is added to obtain a reference voltage coefficient C1 expressed by the following equation (13).

C3-N6+++ΔN4 =NA (i↑1)-Nl・・
-(13) The obtained reference voltage coefficient C1 is shown in FIG. 11 icl. The digital reference voltage coefficient C1 of each of these intensification gradation towns
is stored in the next stage reference voltage data memory] 93.

In this base t$ voltage data memory 193, corresponding Jl quasi-voltage coefficients C3 are stored in pixel order of the 18 Y signals supplied to the signal correction means 6.

Then, the same video signal is input again from the input terminal 1, and the accompanying Y signal is supplied to the A/D converter 191. Meanwhile, in synchronization with this, the reference voltage data memo was released on January 9th.
The reference voltage coefficients CI are sequentially read from A.
/D converter 191. A/I) Converter 1
At 91, the Y signal is A/I) converted using the supplied reference voltage [1 day coefficient CI as the reference voltage] and stored in the frame memory 7.

The corrected frequency 141 at this time is shown in FIG.

Further specific examples of other correction coefficients will be explained with reference to FIG.

In this specific example, if the concentration is 1], there is no more than 100 nIE, or if there is no more ,
Dark connection 4J Rui Figure 13 (21) and 1,11° U
7- and this part with no concentration opening) is reached at 11゛4a0
In addition, in FIG. 13 (δ), the concentration is low. -1)7. D
14.1. )+s frequency is 0. At this time, the complementary iT coefficient distribution and t(, as shown in FIG. 13(b),
Densities D4 to DI3 are set in the same way as in the case of b+ in FIG.
The coefficient correction with the following boosting old slope is applied, and the density is increased.
,,D'1! , a coefficient correction is performed that has a linear decreasing slope toward the density D+5. As a result, the distribution of the reference voltage coefficient 01 based on the ramp function M(11) is as shown in FIG. 1, density DI4
Above this, it becomes a flat state.

By each correction in this way, the A/D conversion characteristic 1♂I (that is, for each degree of the A/D converter 191. The result is as shown in Figure 14. Second, by setting the isometric lowest density gradation of the input image equal to the lowest reference voltage of the A/D converter 91, the contrast after correction can be increased.

Similarly, by applying the same correction to the W horn density portion and J, the contrast can be increased in both directions.

Figure 15 shows M Q+ in Figure 10, voltage coefficient origin/4
201 is an adder, 202 is an average frequency generator, and 203 is a switch.
4 is an integration memory, 205 is a controller, and the 10th
Parts corresponding to the figures are given the same reference numerals.

First, the controller 205 stores the density whose frequency is zero based on the output from the signal correction means 6. At this time, the density with a frequency of zero is successively checked starting from the density D0, and the maximum density among the successive atmospheric degrees is memorized. Similarly, maximum? Blackness D1. The minimum concentration D04 among consecutive zero frequencies from
)Remember. It's more concentrated than this. As reference voltage coefficients CI for -Dl-, first, C1111 to CD1. −
NA' (DI-+ 1) is obtained, and these are transferred to a predetermined address of the reference voltage data memory 193, that is, Y (corresponding to the zero density pixel timing of No. 8) via the switch 203 which is closed to At the same time, these reference voltage coefficients C60''C
II L is supplied to the integration memory 204 for integration storage.

Then, the switch 203 is closed to the fbl side, and Cpl, +
1 to CDII, the data read from the integration memory 204 and the average frequency N from the average frequency generator 202
A and the correction coefficient supplied from the signal correction means 6 via the input terminal 194-1 are added by the adder 201, and the obtained data is used as the Maki quasi-intraocardial pressure coefficient CIIL of the concentration I) t, .
-1 is supplied to the reference voltage data memory 193 and integration memory 204. In the same manner as above, the concentration Dt+g~D
Reference voltage coefficients CDL02 to Cn++ for H are formed and stored in the reference voltage data memory 193. Here, the integration memory 204 is just a memory, and its contents are sequentially increased by a feedback loop.

Formation of the reference voltage coefficient CD, , for the concentration DH.

When the storage is completed, the switch 203 is closed to the fC1 side by the controller 205, and the data in the integration memory 204 is sequentially sent to the reference voltage data memory 193 as delivery voltage coefficients CD841~ for the concentrations D0.1~D2''-1. In this case, the input is cut off in the integration memory 204. As a result, the concentration goes to D8.1・D 2n −
.

The reference voltage coefficient CゎH+I~ is the reference voltage coefficient C1
is constant and equal to

In this case, the delivery voltage positive coefficient for the density C(,+1 to D27/-1 is also stored at the address of the reference voltage data memo January 93 corresponding to the supply timing of the pixels of each density of the Y signal.

FIG. 16 is a block diagram showing still another embodiment of the video printer according to the present invention, in which parts corresponding to those in FIG.
．． Print controller 17. (The No. 8 correction controller 18 is omitted.

In this embodiment, the gradation of the data sent to the line memo January 1 periodically with the printer operation is corrected in accordance with the printer speed. For this reason, the frame memory 7 (FIG. 1) for storing corrected Y signal information becomes unnecessary.

Therefore, first, the Y signal information is read from the frame memory 501, and as explained in FIG. Next, each signal information is simultaneously read out from the frame memories 501 to 503, and one line of Y signal information stored in the line memo January 2 for printing is subjected to gradation correction by the signal correction means 6. The speed of this gradation correction is the horizontal synchronization frequency (approximately 15 KHz), and the variable coefficient means 6
The operation of 04 is sufficient.

In this embodiment, the output of the frame 1 and the memory means 5 is directly supplied to the encoder 15 for the monitor via the D/A conversion means 8. Therefore, an image with exactly the same contrast as the input video signal is displayed on the monitor, and the contrast of the actually printed image is automatically enhanced compared to the monitor image.

FIG. 17 is a block diagram showing still another embodiment of the video printer according to the present invention, and parts corresponding to those in FIG. 10 are given the same reference numerals.

In FIG. 17, in this embodiment, in the A/D converter that A/D converts the primary color signal selected by the signal selector 10, the reference voltage from one correction type A/D conversion means This is to correct the gradation density of one line of primary color signals to be printed.

That is, the Y signal from the LPF 3 is turned into digital Y signal information by the A/D converter 4, and is stored in the frame memory 501. From the Y signal information stored in the frame memory 501, in the same manner as in the seventh embodiment shown in FIG.
/l) The conversion means 19 forms a reference voltage for tone correction in the A/D converter 11.

When this process is completed, the video signal is input again from input terminal 1, and the output of the LPF obtained from this is as follows.
T in real time? G [! R,,G
, one of them was selected at the signal set/lid 10: r1. -rp, /' is supplied to the D converter 11. Δ/[) The corrected output of the transducer 11 is sent to the line memo January 2 in real time, but with the line memory IQ, only the newsletter necessary to print one line is sent to ME. jJ<, the memory name is sent to the halftone control means 13 and the heat sensitive/rad 14. That is, when the line memory length is transferred, the gradation is corrected by the A/D conversion means 11.

In this embodiment, the frame memory 5 shown in FIG.
02,503.7 is unnecessary, and the corrected A/D converted data can be printed periodically during printer operation.

FIG. 18 is a block diagram showing still another embodiment of the video printer according to the present invention, in which reference numeral 20 indicates manual contrast adjustment means, 21 indicates contrast correction amount detection means, and 22
23 is a data correction means; 23 is a D/A conversion means;
Portions corresponding to the figures are given the same reference numerals and redundant explanations will be omitted.

In FIG. 18, first, each signal information is repeatedly read out from the frame memory means 5. These signal information are D/A
The converting means 23 converts the signal into analog Llg information, which is supplied to the encoder 15 via the manual contrast adjusting means 20 for image monitoring. While checking the image on the image monitor, the manual contrast 1 adjustment means is used to adjust the monitor image to the optimum contrast. The contrast adjustment amount at this time is detected by the contrast correction amount detection means 21 to obtain a correction coefficient.

Next, each signal information is read out from the frame memory means 5 for printing, and the gradation of the LY signal information is corrected by the data temperature and pressure means 22 based on this correction coefficient. This corrected Y4ys94 information, (RY), (B-Y
) No. 18 is sent to the RGB conversion means 9 via the 1)/A conversion means 8.

In this way, without changing the signal information in the frame memory means 5 at all, the RGB converting means 9. By sending data from the selector 101 to the line memory 11, data can be corrected at slow timing.

In other words, it is possible to perform data correction processing at a slow timing synchronized with the printing operation without requiring data correction processing in real time, and at the same time, it is possible to check the contrast-corrected image on the monitor.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to automatically and optimally correct the contrast of an input image to obtain a print image of very high quality, and further, to average the contrast density To provide a video printer with excellent functions, which makes it possible to obtain clear contrast in near-uniform density areas, increase the resolution of details of printed images, and solve the problems of the above-mentioned prior art. I can do it.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a video printer according to the present invention, FIG. 2 is a diagram showing an example of the density frequency distribution of an input image, and FIG. 3 is a diagram showing an example of the density frequency distribution of the input image. FIG. 4 is a diagram showing another example of the density frequency distribution of the input image, and FIG.
The figures show a density frequency distribution obtained by correcting this density frequency distribution using the second method in the embodiment shown in Fig. 1, Fig. 6 shows yet another example of the density frequency distribution of an input image, and Fig. 7 The figure shows the density frequency distribution obtained by correcting this using the second method of the embodiment of FIG. 1. FIG. 9 is a diagram showing the density frequency distribution obtained by correcting the density frequency distribution in FIG. 6 using this embodiment, FIG. 10 is a block diagram showing still another embodiment of the video printer according to the present invention, and FIG. 11 is the first
FIG. 12 is a diagram showing the density distribution obtained as a result. FIG. 13 is an explanation of the operation according to another correction method of the embodiment shown in FIG. 10. figure,
Figure 14 is obtained by the correction type A/D conversion means in Figure 10 with the operation shown in Figure 13).

Figures 15 to 18 are diagrams showing other embodiments of the video printer according to the present invention. DESCRIPTION OF SYMBOLS 1... Video signal input terminal, 4... A/1) conversion means, 5... Frame memory means, 501, 502
．． 503... Frame memory, 6... Signal correction means, 601... Data classification means, 602... Density-specific counting means, 603... Density correction determination means, 604...
Variable coefficient means, 605...W degree averaging means, 606.
...Coefficient selection means, 610...Correction coefficient detection means, 7
...Frame memory, 8...I), /A conversion means, 9...RG13 conversion means, group...signal selector, 11...A/D converter, ]2...line memory ,
13... Halftone control means, 14... Thermal head, 1
5...Encoder, 19...Correction Beni A, /
I) 1 stage of conversion, 191...A/D converter, 192
... Base voltage [)/A converter, 193... Jk car voltage data memory, 194...') kY company voltage coefficient generation means, 20... Manual contrast adjustment means, 2I.
. . . last correction amount detection means, 22 . . . data correction means, 23 . . . D/A conversion means. Figure 2 and σ, (b) with white
(烹) Figure 3 (a) and white
r performance no r white
4th figure 5N'↑ 9,7 r mortar
T! Figure 6 Figure 7 Figure 11 (b) ΔNI↑ Figure 1I (C) Do D15 Figure 12 QQ
, L) 15 Figure 73 (a) Figure 13 (C) Figure 14

Claims (6)

[Claims] (1) In a video printer that digitally converts an input video signal and performs halftone control for each predetermined period to print, the video printer includes a first means for detecting a density frequency distribution in one image of the input video signal; a second means for determining a contrast state of the input image according to the input video signal from the frequency distribution and forming correction data; and a third means for correcting the density frequency distribution of the input image using the correction data. . A video printer characterized in that the input image can be printed with contrast emphasized by printing the output of the third means. (2) The video printer according to claim (1), wherein the second means forms the correction data that uniformly disperses the density frequency distribution of the input image in a predetermined density range. . (3) In claim (1), the second means sets a low frequency density on the highest density side of the density frequency distribution of the input image to the maximum density, and a low frequency density on the lowest density side. A video printer characterized in that the correction data is formed to set each density to the minimum density and to uniformly distribute other densities in a range between the maximum density and the minimum density. (4) In claim (1), the second means includes an average frequency N_A of the density frequency distribution of the input image.
and a fourth means for detecting the concentration frequency distribution, and sequentially determines the concentration at which this frequency is accumulated such that the difference between the cumulative frequency number of consecutive concentrations of the concentration frequency distribution and the average frequency is the minimum (K-1
) (where K is an integer from 0 to the number of density gradations in the predetermined density range). )
and a fifth means for forming a coefficient to be the second concentration;
A video printer characterized in that the coefficient is used as the correction data. (5) In claim (1), the second means forms a reference voltage according to the frequency for each density of the input image as the correction data, and the third means forms an analog /digital conversion means, by supplying the reference voltage according to the density of the supplied input image to the analog/digital conversion means;
A video printer characterized in that the conversion characteristics of digital conversion means are changed. (6) In claim (1), the first means is a monitor means for the input image, and the second means adjusts the contrast of the monitor image and applies a correction amount according to the adjustment amount. A video printer characterized in that it is a means for detecting.