JPH066608A - Picture output device - Google Patents

Abstract

PURPOSE:To realize the picture output device able to obtain an output picture subject to excellent density correction from the initial stage without need of density correction for each display data output and without need of preparing of separate large capacity data storage area from a display memory in the picture output device displaying at first outline of the picture while receiving picture data of a low frequency component sequentially and outputting the picture gradually with high definition. CONSTITUTION:One pattern of DCT picture data 106 is inputted from a DC component at first, a DC density correction section 102 implements density correction in matching with the characteristic of an output device, a decoding section 103 implements decoding and the result is outputted and displayed by a picture display section 104. AC data inputted succeedingly are directly inputted to the decoding section 103 without special density correction processing and decoding/display is implemented in a form that decoded data are simply added to the DC component having been subject to density correction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention receives gradation image data converted into frequency data by a method such as discrete cosine transform (hereinafter referred to as DCT or DCT transform), and displays them in order from low frequency components. The present invention relates to an image output device.

[0002]

2. Description of the Related Art Before describing a conventional example, the principle of image data coding by orthogonal transformation will be briefly described. The transform coding by orthogonal transform is to realize efficient coding by removing the correlation between sample values by transforming the sample values into mutually orthogonal coordinate systems. In addition, data is compressed by converting to frequency components, allocating a large number of bits to low-frequency components where power is concentrated and visual power has a great influence, and high-frequency components are quantized with a small number of bits. Improve sex. Orthogonal transformation for transforming an image into frequency components includes Hadamard transformation and DCT.

Next, DCT and its inverse transformation (hereinafter referred to as IDCT
An example in which 8 × 8 pixels are coded as one block will be described with reference to FIG. The original image data is divided into blocks of 8 × 8 pixels and converted in block units. According to the relative position of each pixel in one block, the upper left pixel is the zeroth data of the origin, and the data of the i-th pixel in the right direction and the j-th pixel in the downward direction is f (i, j) (0 ≦ i <8, 0 ≦ j <8, i and j are integers). The origin data in the upper left corner is f (0,
0) and the data in the lower right corner is f (7,7). DC at this time
The T-transformed data F (u, v) (0 ≦ u <8, 0 ≦ v <8, u, v are integers) is

[0004]

[Equation 1]

It becomes like.

F (0,0) represents a value corresponding to average data in the image block, and is called a DC coefficient in the sense of a DC component. In the case of Expression 1, it is actually eight times the average value of the data in the block. The other 63 elements represent AC components and are also called AC coefficients. The larger the values of u and v in Expression 1, the higher the frequency component. When data compression is performed, the fact that the higher the frequency component in a natural image is, the smaller the amount is, and the sensitivity of the human eye is also reduced, the lower bits of the high frequency component are discarded and quantization is performed with a small number of bits. .

The inverse discrete cosine transform (IDCT) for obtaining f from F is

[0008]

[Equation 2]

[0009] However, c (u), c (v) in Equation 2
The definition of is the same as in the case of Expression 1. As an example of an image compression method applying DCT, JPEG (Joint P
photographic Expert Group)
There are standards: 1) Two-dimensional DCT 2) Quantization of DCT coefficients to appropriate precision 3) Huffman coding of quantized DCT coefficients Highly efficient compression with little deterioration in image quality is performed by the above procedure. ing.

Conventionally, as a system for transmitting and displaying DCT-converted gradation image data in order from a low frequency component, Japanese Patent Laid-Open No. 10573/1993, "Transmission method of DCT-SQ compressed image data and its data processing". There was something like a device.

In the transmission method of this conventional example, the data F (u, v) obtained by DCT-transforming the original image data with 8 × 8 pixels as one block is set to have a lower frequency as u + v becomes smaller, and u + v is set. Data is transmitted in ascending order of the value of. First, the component of F (0,0), that is, the DC component is first sent for one screen, and then F (1,0) and F
The component of (0, 1), and then F (0, 2), F
Transmission is performed in the ascending order of u + v value, such as the components of (1, 1) and F (2, 0).

On the image receiving device side which receives the transmitted data, the received low frequency component is immediately transmitted to the display device for display. As a result, on the display device, the outline of the image based on the low frequency component is first displayed at high speed, and thereafter, the definition of the displayed image is gradually increased as the higher frequency component is transmitted. For example, in the case of this conventional example, the number of DC component data is 1/6 of all frequency data.
Since there are only four, it is shown that the first outline of the entire surface of the image can be seen as soon as the transmission of 1/64 of the entire frequency data is completed.

[0013]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The conventional technique of No. 1 had a feature that an outline of an image could be displayed at an early stage when a low-frequency component with a small amount of data was received, but the gamma characteristic of input image data and the gamma characteristic of an image display device are different. Thus, a problem arises when a data correction process such as density correction is required to display a good image. Normally, data processing such as density correction can be executed only after the decoding of the image is completed and the final decoded image data is obtained. If you play around with it,
It interferes with the decryption work. For this reason, in order to prevent the original decoding work from being hindered while performing good density correction for display on the data being decoded, save the data in the decoding process. The data storage area to be stored and the image output area for outputting the data for image display are completely separate, and the density correction data is added to the image data each time the rough image data decoded up to the specific frequency data is completed. It had to be created and output to the image output area.

In such a structure, the video memory for displaying an image cannot be used also as a decoding process data storage area, and there is a problem that a data storage area must be prepared separately.

Further, each time the rough image data is created,
There is also a problem that it is necessary to perform density correction processing on the image data every time and output the image data to the image output area, which takes time.

The present invention has been made in view of such a problem, and its purpose is to receive low-frequency components of an image in order, display an outline of the image first, and then gradually increase the resolution. In an image output device that outputs various images, it is not necessary to prepare a large-capacity data storage area separately from the display memory, and even if density correction is not performed every time the display data is output, the initial stage It is to realize an image output device capable of obtaining an output image with excellent density correction.

[0017]

The image conversion apparatus of the present invention is an image output in which data obtained by converting gradation image data into spatial frequency components is used as input data, and the input data is input first from DC component data. A device, said DC
It is characterized by comprising a DC density correction unit for performing density correction on component data, a decoding unit for decoding input data for each frequency component, and an image display unit for displaying data in the decoding process.

[0018]

EXAMPLE The inverse discrete cosine transform (IDCT) equation of equation 2 is

[0019]

[Equation 3]

However,

[0021]

[Equation 4]

Can be rewritten as
Decoding work for f (i, j) is performed by "f (i, j with initial value 0.
For j), k (i, j, u, v) F (u, v) is gradually added for all u, v ”. In the above decoding process, when u, v take a specific value, the operation of adding k (i, j, u, v) F (u, v) is specifically referred to as “component of frequency u, v”. Decryption ”. That is, certain frequencies u, v
Decoding the components of fr (i, j) = f (i, j) + k (i, j, u, v) F (u, v) (i = 0,1, ..., 7, j = 0,1, ..., 7) It is expressed by Equation 5 as in (5).

An embodiment of the image output apparatus of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the image output apparatus of the present invention.

The image input unit 101 has a D
The DCT image data 105 converted into frequency data using CT is input. The DCT image data 105 may be obtained directly from a file in the magnetic disk storage device or a communication line, or may be obtained in the decoding process of data compressed according to the JPEG standard or the like.

In this embodiment, the DCT image data 105
Is first input for one screen from the DC component.

The input DC component data 106 is DC
The density correction unit 102 is entered.

The DC density correction unit performs density correction on the received DC component data in accordance with the characteristics of the output device.
For example, when the data output device is a CRT display having an output characteristic with a gamma value of 2.2, the input data D
for in

[0029]

[Equation 5]

The density correction as described above is performed to obtain correction data Dout for display. However, the above equation is an equation when Din is standardized in the range of 0 to 1, and in fact, a constant term is added according to the range of Din. For example, Din, that is, D
When the C component data is in the range of 0 to Dmax,

[0031]

[Equation 6]

It becomes as follows.

The decoding unit 103 includes a DC density correction unit 102.
The DC data whose density has been corrected by the new DC data F
As (0,0), k (i, j, u, v) F in Equation 5
(U, v) is obtained and the result is output to the image display unit 104.

A more detailed embodiment of the image display unit 104 is shown in FIG. The image display unit 104 of this embodiment includes a video memory 201, a display controller 202, and a CRT display 203, and the decoded data output to the image display unit 104 by the decoding unit 103 corresponds to the corresponding pixels in the video memory 201. It is added to the data. As a result, k (i, j, u, v) F is added to f (i, j) in Expression 5.
The process of adding (u, v) is realized. Since the initial value of the image data on the video memory 201 is set to zero, f (i, j) on the right side of Expression 5 becomes zero in the step of processing the first DC component, and k is stored in the video memory.
(I, j, u, v) is equivalent to writing F (u, v) as it is. Display controller 202
Reads out the image data of the video memory 201, DA-converts it, and outputs the video signal 204 for CRT display.
Is output and the image is displayed on the CRT 203.

When the above steps are completed, the schematic view of only the DC component of the image is displayed with the density corrected so as to fit the output device. In the case of block size 8 × 8 DCT conversion, the number of DC component data is 1 of all data.
Since it is only / 64, the trouble of performing the density correction processing on the DC component data is very small.

Next, as the DCT image data 105,
AC component data is input. When transmitting from a small u + v value as in JP-A-3-10573, frequency components F (0,1) and F (1,0) at which u + v = 1 next, and further u + v = 2. However, the AC component data 108 is directly input to the decoding unit 103 without density correction. After that, as in the case of DC data, the decoding unit 103 obtains k (i, j, u, v) F (u, v) and outputs it to the image display unit 104.
CRT display 20
3 is displayed above.

As described above, in the present invention, the density conversion process is not performed on all image data, but only on the DC component. If you increase or decrease the DC component value,
All data in the block changes by the same amount. For example, when decoding the DCT data using the equation 4, changing the DC component F (0,0) by a certain value X means that all the data after decoding is changed uniformly by X / 8. Is equivalent. This shows that the density correction according to each pixel data after decoding is not performed, but this also does not cause a big problem when a natural image with a small AC component is targeted, A much better density-corrected image is displayed as compared with the case where no density correction is performed.

In this embodiment, the DC density correction unit 10
Although a simple gamma conversion process is described as the density correction process in 2, various other density conversion processes such as a process for enhancing contrast can be considered. Further, these arithmetic processing may be performed by a central processing unit of a computer by software arithmetic, or a hardware arithmetic unit configured by means of combining multipliers and adders by electronic circuits or the like may be used.

[0039]

As described above, since the image output apparatus of the present invention is constructed so as to immediately perform the density correction on the DC component data transmitted first, it is possible to perform the density correction from the initial stage.
The density-corrected schematic image data according to the characteristics of the output device can be seen, which is very effective for early confirmation of the image.

Further, the density correction is carried out only for a very small amount of DC component data, and the trouble and time required for the density correction processing hardly poses a problem. Even if no special correction processing is performed on other AC component data, it has a sufficient effect on a natural image in which the AC component level is not so large.

Further, after the density correction processing is performed on the DC component data, the AC component data may be normally decoded. Therefore, for the density correction, a special memory area is secured and the decoding process is performed. There is no need to save the data of.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an embodiment of an image display unit of the present invention.

FIG. 3 is a diagram showing DCT conversion.

[Explanation of symbols]

 101 image input unit 102 DC density correction unit 103 decoding unit 104 image display unit 105 DCT image data 106 DC component data 107 density correction DC data 108 AC component data 109 decoded data

Claims (1)

[Claims] 1. The input data is data obtained by converting gradation image data into spatial frequency components, and the input data is D.
An image output device in which C component data is input first, a DC density correction unit that performs density correction on the DC component data, a decoding unit that decodes input data for each frequency component, and a decoding process An image output device comprising: an image display unit for displaying data.