JPH0638044A - Method and device for calibrating image data - Google Patents

Abstract

PURPOSE:To provide images for which tone jump does not stand out. CONSTITUTION:An adder 34 adds a random number outputted from a random number generator 32 to the low-order data of output data from a calibration table 30 and adds the carry data to the least significant bit of the high-order data of output data supplied to an adder 36. As a result, the least significant bit of high-order data is set at prescribed probability and image data to provide the images, for which tone jump does not stand out practically, are generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data calibration method and apparatus capable of obtaining output image data in which tone jumps are inconspicuous from input image data.

[0002]

2. Description of the Related Art When image data obtained by an image input device such as a scanner is output as a visible image by an output device,
The image data needs to be calibrated. This is because the output characteristics of the output device generally differ depending on the model.

FIG. 7 shows a calibration table for converting input image data into output image data.
In this case, the output image data after conversion in the area A is shown in FIG. 8A, and the output image data after conversion in the area B is shown in FIG. 8B. A plot of these is shown in FIGS. 9 (A) and 9 (B).

[0004]

By the way, when the image data is calibrated in this way, smooth conversion is not performed between the input and output image data, and so-called tone jump occurs. In other words, for example, when 8-bit (256 gradations) input image data is converted to 8-bit output image data, 256 gradations cannot be substantially obtained.

Therefore, the present invention has been made in view of the above-mentioned inconvenience, and it is possible to secure a substantial number of gradations in the output image data and to obtain a good image in which tone jumps are not noticeable. An object of the present invention is to provide a calibration method and device.

[0006]

In order to achieve the above object, the present invention provides a first step of converting N-bit input image data into M-bit image data according to the output characteristics of an image output machine. A second step of adding a K-bit random number to the lower K bits (M> K) of the M-bit image data, and the upper step (M-) of the image data obtained in the second step.
And a third step of extracting K) bit image data as output image data.

According to the present invention, a storage means for holding a calibration table for converting N-bit input image data into M-bit image data according to the output characteristics of the image output device, and at least K bits (M> K). ), A random number generating means for generating a random number, and an adding means for adding the K-bit random number to the lower K bits of the M-bit image data.
Output image data generation means for extracting, as output image data, image data of upper (M-K) bits of the image data to which the random numbers have been added.

[0008]

In the method and apparatus for calibrating image data according to the present invention, N-bit input image data is converted into M-bit image data by the calibration table and then converted into lower K bits of the M-bit image data. Add a random number. In this case, the (K + 1) -th bit data from the lower order of the M-bit image data is "1" or "0" with a probability corresponding to the lower K-bit data.
Is set to. Therefore, if the upper (M−K) bits of the M-bit image data are used as the output image data, a smooth image in which tone jumps are averaged can be obtained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method and apparatus for calibrating image data according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 shows an image processing system 10 for performing processing of inputting, editing, and outputting an image. The image processing system 10 includes nodes 14 a to 1 of the network 12.
4d connected to the image input device 16, editing workstation 18, image processing device 20 and image output device 2
2 is provided.

The image input device 16 reads the image information of a document to obtain input image data, and supplies this input image data to the editing workstation 18 via the nodes 14a and 14b. The editing workstation 18 processes the input image data based on various plate making conditions and outputs the processed image data to the image processing apparatus 20 via the nodes 14b or 14c and 14d. The image processing device 20
The input image data is converted according to the resolution and density characteristics of the image output device 22, and the input image data is converted into a halftone dot signal. The image output device 22 creates an original film for plate making by outputting an image based on the halftone dot signal on the film.

FIG. 1 shows a detailed configuration of an image processing apparatus 20 in the image processing system 10 configured as described above. The image processing apparatus 20 includes an interface 24 that receives input image data from the node 14d, an input buffer 26 that temporarily holds the input image data,
A density converter 28 for converting the density of the input image data corresponding to the image output device 22, a calibration table 30 (storage means) for calibrating the input image data according to the output characteristics of the image output device 22, Random number generator 3
2 (random number generating means), an adder 34 (adding means) for adding the random number from the random number generator 32 to the lower bit of the calibration table 30, and the adder 34 to the upper bit of the calibration table 30. Adder 36 (output image data generation means) for adding the output image data, the halftone dot signal generator 38 for generating a halftone dot signal based on the output image data of the adder 36, and the halftone dot signal temporarily. And an interface 42 for transmitting the halftone dot signal as output image data to the image output device 22.

The calibration table 3
For example, 0 is set so that the image output device 22 outputs a step edge to the film, the step edge is measured using a densitometer or the like, and the density is calibrated.

Next, a calibration method in the image processing apparatus 20 configured as above will be described with reference to FIG. The input image data supplied to the image processing apparatus 20 via the node 14d is 8 bits, and the conversion in the calibration table 30 is 8 bits-16.
The following description will be given assuming that the random number output from the bit conversion / random number generator 32 is 8 bits and the output image data output from the image processing device 20 is 8 bits.

The input image data as the dot% data supplied from the editing workstation 18 is temporarily held in the input buffer 26 via the interface 24.
Next, in the density converter 28, the input image data is converted into image data having a pixel density corresponding to the resolution of the image output device 22 by calculation processing such as interpolation.

Next, the 8-bit image data whose pixel density has been converted is converted into 16-bit image data by the calibration table 30. The calibration table 30 is set as shown in FIG. In the 16-bit image data, the lower 8 bits are supplied to the adder 34, and the upper 8 bits are supplied to the adder 36.

On the other hand, the adder 34 is supplied with an 8-bit random number from the random number generator 32. Therefore, in the adder 34, the lower 8 bits of the image data output from the calibration table 30 and the 8 bits of the random number are added, and the carry data (9th bit data) of the addition result is added by the adder. 36. In this case, the upper 8 bits of the image data output from the calibration table 30 are supplied to the adder 36, and the carry data from the adder 36 is added to the least significant bit of the image data. It As a result, the adder 36
Outputs image data in which the least significant bit is set with a probability determined by the lower 8 bits of the output of the calibration table 30.

FIGS. 4A and 4B show specific examples of output image data from the adder 36 corresponding to the areas A and B in FIG. In this case, since the least significant bit of the output image data fluctuates momentarily with a constant probability due to the random number of the random number generator 32, the averaged image data (for example, 1.4 and 2) is averaged. .8 etc.) will be obtained. FIGS. 5A and 5B are plots of the output image data of the areas A and B thus obtained. It will be appreciated that good image data with less noticeable tone jump can be obtained, as compared with the case of the conventional technique shown in FIGS. 9A and 9B.

The number of bits of image data that can be handled can be generalized as shown in FIG. That is, in the calibration table 30, N-bit image data is converted into M-bit image data, and a K-bit random number is added to the lower K bits (M> K) by the adder 34. Then, in the adder 36,
By adding the carry data from the adder 34 to the least significant bit of the upper (M−K) bits of the image data,
Image data with less noticeable tone jump can be obtained.

The image data obtained as described above is
It is supplied to the halftone dot signal generator 38, converted into halftone dot data, and then once held in the output buffer 40, and then supplied to the image output device 22 via the interface 42. The image output device 22 records a desired image on a film or the like based on the halftone dot data.

[0021]

According to the method and apparatus for calibrating image data of the present invention, it is possible to generate a halftone image, thereby ensuring a substantial number of gradations in the output image data and performing a tone jump. It is possible to obtain a good image inconspicuous.

[Brief description of drawings]

FIG. 1 is a calibration block diagram of an image processing apparatus to which an image data calibration apparatus according to the present invention is applied.

FIG. 2 is a calibration diagram of an image processing system including the image processing apparatus shown in FIG.

FIG. 3 is a detailed block diagram of a main part in the image processing apparatus shown in FIG.

4 is an explanatory diagram of a relationship between input image data and output image data in the image processing apparatus shown in FIG.

5 is a plot of the data shown in FIG.

FIG. 6 is an explanatory diagram of an image data calibration method according to the present invention.

FIG. 7 is an explanatory diagram of a calibration table.

FIG. 8 is an explanatory diagram of a relationship between input image data and output image data in the related art.

9 is a plot of the data shown in FIG.

[Explanation of symbols]

 10 ... Image processing system 16 ... Image input device 18 ... Editing workstation 20 ... Image processing device 22 ... Image output device 30 ... Calibration table 32 ... Random number generator 34, 36 ... Adder 38 ... Halftone dot signal generator

Claims (3)

[Claims] 1. A first conversion of N-bit input image data into M-bit image data according to the output characteristics of an image output machine.
Process, a second process of adding a K-bit random number to the lower K bits (M> K) of the M-bit image data, and a high-order (M−K) of the image data obtained in the second process. )
And a third step of extracting bit image data as output image data, and a method of calibrating image data. 2. The method for calibrating image data according to claim 1, wherein M> N. 3. Storage means for holding a calibration table for converting N-bit input image data into M-bit image data according to the output characteristics of an image output machine, and at least K-bit (M> K) random numbers. Random number generating means for generating; addition means for adding the K-bit random number to lower K bits of the M-bit image data; and upper (M−K) -bit image data of the image data to which the random number is added. An image data calibration device, comprising: output image data generation means for extracting the image data as output image data.