JPH01253367A - Image processor - Google Patents

Abstract

PURPOSE:To realize a MTF correction in accordance with picture data to be read by deciding the character and symbol parts out of the read image data via a line image part deciding part and switching MTF correction parameters based on the information on said decision. CONSTITUTION:The read image data are successively converted into digital signals by an A/D converting part 3 and stored temporarily in a memory 4. A line image part deciding part 5 decides the presence or absence of characters, symbols, etc., based on the density difference between the data on a noted picture element and the data on the picture element contiguous to the noted picture element which are read out of the memory 4. The information on said decision in inputted to a selector 6 and the MTF correction parameter set previously at the selector 6 is selected and seat to a MTF correction circuit 7. While the image data received from the part 3 undergoes such processes as magnification, reduction, masking, etc., through an image processing part 8 and is sent to the circuit 7. The image resolution of the image data is corrected by the circuit 7 in accordance with the picture quality and transferred to a multi-level circuit 10 for printer recording.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image processing apparatus that can correct the resolution of read image data according to the properties of the image.

[Foreground of invention]

Image quality of image data read from a document deteriorates due to factors in the reading element, optical system, and other signal transmission systems, and the dynamic range decreases. Therefore, conventionally, in order to quantitatively evaluate such deterioration, % MT F (Mod
ulation Transfer Function
) was used. This MTF is the maximum density value (brightest density value) of the read image density relative to the reference density.
□,, It was determined from the lowest density value (darkest density value) V min.

To correct this MTF, for example, Fourier transform,
Inverse transformation, convolution transformation, etc. are performed.

[Problem to be solved by the invention]

However, in the past, such MTF correction was performed using a specific fixed method regardless of the nature of the input image data, so it was not possible to correct the MTF depending on the nature of the image, such as correction suitable for photographs, correction suitable for line drawings, etc. could not be done.

An object of the present invention is to make it possible to perform MTF correction adapted to the characteristics of a document.

[Means to solve the problem]

For this purpose, the present invention is configured to provide a line drawing portion determining means for determining character and symbol data from image data, and to switch the MTF correction parameters based on the determination information obtained by the determining means.

〔Example〕

Examples of the present invention will be described below. FIG. 1 is a block diagram of one embodiment. The image of the original document 1 is read by the scanner section 2 in the main scanning direction and the sub-scanning direction, and the read image data is sequentially converted into a digital signal by the A/D conversion section 3 and temporarily stored in the memo IJ 4. In addition,
In the A/D converter 3, shading correction is also performed simultaneously by adjusting the reference voltage. Then, based on the density difference between the data of the pixel of interest read out from the memory 4 and the data of its adjacent pixels, a line drawing part determining section 5 judges whether the pixel is a character, symbol, etc., that is, a line drawing part.

Next, the determination information from the line drawing portion determination section 5 is input to the selector 6, and the MTF correction parameter set in advance in the selector 6 is selected and transferred to the MTF correction circuit 7. On the other hand, the image data output from the A/D conversion section 3 is subjected to enlargement, reduction, masking/trimming, ghost removal, and other processing in the image processing section 8, and then transferred to the MTF correction circuit 7 through the memory 9. There, the resolution is corrected according to the image quality, and the image is transferred to the multi-value conversion circuit 10 for printer recording.

Now, for example, when a document 11 in which a photograph part A and a character symbol part B are written on a white background is read along scanning line a as shown in FIG. 2, the density level of each part is as shown in FIG. 3. Become. The top is the white level of the background, and the bottom is the black level of the characters and symbols.

Here, the density difference S in the photo area A with the adjacent pixel is small and is X, but the density difference S in the character symbol area B is large Y.

Therefore, in the present invention, the above-mentioned line drawing portion determining section 5 detects the density difference S between the image data of the pixel of interest and the image data of the adjacent pixel, and determines the image quality with respect to the density difference S as follows.

■Photograph painting... S<Sl ■Halt painting...S1≦S≦82■Character symbol drawing
... 32<S For example, in the case of 64 gradations, 51=5.52=19.

Therefore, the selector 6 includes MTF correction parameters for photographic images, MTF parameters for halftone images, and MTF parameters for character and symbol images.
By storing TF correction parameters in advance and selecting one of them based on the judgment information from the line drawing part judgment section 5 and using it as the MTF correction parameter of the MTF correction circuit 7, the image MTF correction can be performed depending on the properties.

For example, when performing edge emphasis correction in the - dimension (main scanning direction), a correction factor having a characteristic as shown in FIG. 4 is used. (1) to (4) are edge enhancement, (5) is no correction, and (6) is smoothing. Therefore, the coefficients X of the three types of edge enhancement filters are selected from among these, and
By storing the information in the image data and selecting and using it based on the determination information from the line drawing portion determining section 5, it is possible to perform edge enhancement that is appropriate for the image quality.

In addition, when performing MTF correction using convolution Silane transformation, a 3×3 matrix convolution filter is often used, for example, the following matrix is used. Three types of these matrices are prepared. , are selected and used by the selector 6 as described above.

〔Effect of the invention〕

As described above, according to the present invention, the line drawing part determining section determines the characters and symbols in the read image data, and the MTF correction parameters are switched based on the determination information. MTF according to characteristics
You will be able to make corrections.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an image processing apparatus according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of a document, FIG. 3 is a waveform diagram of a read image signal along line a of the document in FIG. FIG. 4 is a characteristic diagram of the MTF correction factor for edge enhancement. Agent Patent Attorney Tsuneaki Nagao Printer

Claims (1)

[Claims] (1) In an image processing apparatus that performs MTF correction of image data of a read document, a line drawing portion determination means for determining character and symbol data from the image data is provided, and the MTF is adjusted based on the determination information obtained by the determination means. An image processing device characterized by switching correction parameters.