JP2002369036A - Image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce image quality deterioration at printing or monitoring caused by a type of a solid-state image pickup element of a digital camera. SOLUTION: When a smart media (R) 23 extracted from a digital camera 22 is set to a card reader 13, an image file memory 14 stores an image file and a DPOF(Digital Print Order Format) file memory 15 stores a DPOF file. A controller 20 reads camera information from the DPOF file to discriminate whether the solid-state image pickup element of the digital camera 22 is of a honeycomb type or a Bayer type, selects a corresponding filtering coefficient from a coefficient memory 16 and gives the selected coefficient to an image processing section 17. The image processing section 17 applies the filtering coefficient to image data read from the image file memory 14 to apply filter processing to the data and displays an image on a liquid crystal display panel 18. When a user operates an operation section 19, the image data subjected to the filter processing are fed to a print section 21, to print out the image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image processing method for performing image processing on image data obtained by photographing with a digital camera, and more particularly to an image processing method for reducing deterioration of image quality.

[0002]

2. Description of the Related Art A digital camera converts an optical subject image formed on a photocathode of a solid-state image sensor such as a CCD image sensor disposed behind a photographic lens into a digital signal and stores the digital signal in a built-in memory or an auxiliary storage device. I do. As this auxiliary storage device, for example, a memory card such as a smart media is used. Generally, image data recorded on a memory card is stored in a personal computer (hereinafter referred to as a personal computer) via a card reader or the like, and then printed by a printer such as an inkjet printer connected to the personal computer.

When the image data is subjected to signal processing as it is and printed, the outline of the image is often blurred and the sharpness is reduced. For this reason, it is common that sharpness correction is performed. This sharpness correction is performed by a filter process called a second derivative operation (Laplacian). More specifically, the contour of an image is enhanced by changing the density value of a certain pixel in accordance with the density values of surrounding pixels.

On the other hand, when the frequency component of the subject exceeds the Nyquist frequency determined from the pixel pitch, moire appears. For this reason, many digital cameras combine multiple quartz plates called optical low-pass filters,
High frequency components are removed.

[0005]

The solid-state image pickup devices used in digital cameras include a general Bayer type CCD and a honeycomb type CCD proposed by the present applicant.
There are CDs, which have direction dependency on the spatial frequency (resolution) due to the difference in pixel arrangement. That is, in the Bayer CCD, square pixels are arranged in a grid pattern, and the pixel pitch in each diagonal direction is narrower in the diagonal direction than in the horizontal and vertical directions, so that the spatial frequency in the diagonal direction is high. On the other hand, the honeycomb type CCD has the pixels of the Bayer type CCD arranged at an angle of 45 degrees. Contrary to the Bayer type CCD, the pixel pitch in the horizontal and vertical directions is narrower than in the diagonal direction. Has a higher spatial frequency. Therefore, when sharpness correction suitable for image data captured by a digital camera using a Bayer CCD is directly applied to image data captured by a digital camera using a honeycomb CCD, and vice versa. In this case, there is a problem that a false color is emphasized or a false contour is emphasized and printing is performed, and the image quality is rather deteriorated. This problem also occurs when displaying an image on a monitor.

[0006] The low-pass filter incorporated in the digital camera may not be ideal in terms of cost or the like, or may not be incorporated at all. If image data obtained by photographing with such a relatively low-cost digital camera is simply subjected to sharpness correction and printed, moiré is emphasized and image quality deteriorates.

Another object of the present invention is to provide an image processing method for reducing deterioration in image quality during printing or monitoring due to the type of solid-state imaging device of a digital camera, the presence or absence of a low-pass filter, and the like. .

[0008]

According to another aspect of the present invention, there is provided an image processing method for performing image processing on image data obtained by photographing with a digital camera. Preparing a plurality of filtering coefficients for reducing image quality deterioration caused by camera information of the camera, selecting a filtering coefficient according to the camera information from the plurality of filtering coefficients,
It is used for the image processing. The camera information is information indicating a type of a solid-state imaging device used in the digital camera. Further, the camera information is information indicating the presence or absence of a low-pass filter. Further, the image processing includes a filter processing for applying different filtering coefficients to each of luminance data and color difference data created from the image data.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of a printer embodying the present invention.
3, an image file memory 14, a DPOF file memory 15, a coefficient memory 16, an image processing unit 17, a digital liquid crystal panel 18, an operation unit 19, a controller 20, and a printing unit 21. The smart media 23 used in the digital camera 22 is set in the card reader 13, and the image file and the DPOF file (see FIG. 2) recorded on the smart media 23 are read. The DPOF file is a standard D for automatically printing a desired image from an image taken by a digital camera by an image output device such as a photo printer.
This file is based on the POF (Digital Print Order Format).

In FIG. 2 showing the directory structure of the smart media 23, a root directory "Root" is shown.
, "IM_1", "IM_2", ..., "I
M_n ”and“ MISC ”subdirectories are created. Subdirectories “IM_1” to “IM”
_N ”is an image file 25a to 25 of each captured image.
n is recorded for each screen, and the sub-directory “MIS
The DPOF file 26 is recorded in "C".

The image file 25 is stored in the digital camera 22.
The image data processing circuit has a predetermined signal processing performed by the image data 27a, and image accompanying information 27b corresponding to the image data 27a. The image data 27
a is composed of R (red), G (green), and B (blue) image data. As the image accompanying information 27b, a photographing date and time, a photographer, a photographing place, photographing conditions (exposure conditions, shutter speed, and the like), an ID number of the photographing device, and the like are recorded. The image accompanying information 27b is automatically recorded when the image data 27a of the photographed subject image is recorded on the smart media 23 based on the information set before the photographing, and is manually operated by the user using the operation panel after the photographing. Can also be recorded.

The DPOF file 26 contains camera information,
Image reproduction information 26a such as print job information and image source information is recorded. The camera information includes type information of the solid-state imaging device indicating whether the solid-state imaging device used in the digital camera 22 is a honeycomb CCD or a Bayer-type CCD, and a low-pass indicating whether or not a low-pass filter is used in the digital camera 22. There is information on the presence or absence of a filter. The type information of these solid-state imaging devices and the information on the presence / absence of a low-pass filter are stored in the camera model name, for example, “FinePix
00z "(product name), only the camera model name may be recorded as camera information. It is assumed that a low-pass filter is used in the digital camera 22 of the present embodiment. The print job information indicates print conditions such as the number of prints and the size. The image source information indicates the type of the file format and the like.

In FIG. 3, which shows a part of a Bayer type CCD, a Bayer type CCD 30 has a light receiving portion of each pixel 31 where P is an arrangement pitch between pixels in a horizontal direction (X direction) and a vertical direction (Y direction). 32 has a square shape. In the Bayer-type CCD 30, the pixel interval in the diagonal 45-degree direction is P / √2, and the resolution in the diagonal 45-degree direction is higher than in the horizontal and vertical directions. A color filter having each of R, G, and B colors is mounted on each light receiving section 32. Since only one color filter can be attached to one pixel, the final color image data is derived by calculation based on information on surrounding pixels.

In FIG. 4, which shows a part of a honeycomb CCD, a honeycomb CCD 35 rotates pixels of the Bayer CCD 45 degrees and sets each arrangement pitch between pixels in the X and Y directions to P / √2. As a result, the resolution in the horizontal and vertical directions is higher than that in the 45 ° oblique direction. Further, since the shape of the light receiving portion 37 of each pixel 36 is an octagon close to a circle and the area of the light receiving portion 37 is increased, the sensitivity is higher than that of a Bayer type CCD of the same size. Each light receiving section 37
A color filter having each of R, G, and B colors is mounted on the top, and similar to the Bayer type CCD 30, final color image data is calculated based on information of surrounding pixels. Is derived by

The smart media 23 on which the image photographed by the digital camera 22 is recorded is transferred to the card reader 13.
, The image file 25 of the smart media 23 is read into the image file memory 14 and the DPOF file 26 is read into the DPOF file memory 15.

The coefficient memory 16 stores the following mathematical expressions 1 and 2 indicating the coefficients (filtering coefficients) of the spatial filter when the position of the 3 × 3 pixel is (i, j).

[0017]

(Equation 1)

[0018]

(Equation 2)

F1 (i, j) represented by equation (1) is a filtering coefficient applied when the solid-state image pickup device of the digital camera 22 is a honeycomb type CCD, and is an oblique direction having a lower resolution than the horizontal and vertical directions. Sharpness correction is performed by using a low pixel density value to reduce false color and false contour enhancement.

In FIG. 5, which shows a part of image data obtained by photographing with a digital camera using a honeycomb type CCD 35, a sharpness correction is performed by applying a filtering process by applying Equation 1 to the image data. Pixel 4
The density values of the four pixels 41 to 44 at the position of 45 degrees oblique to 0 are multiplied by a coefficient “− ／”, respectively, and these are added to the original density value of the pixel 40 to correct the sharpness of the pixel 40. Density values are obtained. The X and Y directions shown in the drawing correspond to the X and Y directions of the honeycomb CCD 35 shown in FIG. 4, and the main scanning in which heating elements of a thermal head of the printing unit 21 described later are arranged in a line. Direction and a sub-scanning direction, which is a paper feed direction orthogonal to the direction.

F2 (i, j) represented by Expression 2 is a filtering coefficient applied when the solid-state image pickup device is a Bayer type CCD, and is opposite to the case of the honeycomb type CCD in a diagonal direction. Sharpness correction is performed by using low density values of pixels in the horizontal and vertical directions with low resolution to reduce false color and false contour enhancement.

In FIG. 6 showing a part of image data obtained by photographing with a digital camera using the Bayer type CCD 30, a sharpness correction is performed by applying a filtering process to the image data by applying Expression 2. Pixel 5
The sharpness correction of the pixel 50 is performed by multiplying the density values of the four pixels 51 to 54 at the X and Y directions of 0 by a coefficient “− 係数”, respectively, and adding these to the original density value of the pixel 50. The obtained density value is obtained.

The image file memory 14 performs a reading operation under the control of the controller 20, and stores the image file 2
5, the image data 27a is sequentially read out for each of R, G, and B, and sent to the image processing unit 17. This image processing unit 17
For each of the R, G, and B image data, a filtering coefficient corresponding to the type of the solid-state imaging device is read from the coefficient memory 16 and the filtering process is performed. Image data 27
a is displayed as a thumbnail.

When an image desired to be printed is selected from the images displayed on the liquid crystal panel 18 and the print start key is operated by operating the selection key of the operation unit 19, the filtered image data is transmitted from the image processing unit 17. It is sent to the print unit 21. As the print unit 21, for example, a well-known color thermal printer that color-records a color image in three color planes sequentially using color thermal recording paper in which thermal color layers that respectively develop yellow, magenta, and cyan colors are laminated is used. In this case, the image data is converted from RGB to YM before being sent from the image processing unit 17 to the printing unit 21.
The color is converted to C.

The operation of the thus constructed printer 10 will be described. After photographing with the digital camera 22, the user puts the used smart media 23 into the printer 1.
0 is set in the card reader 13. Card reader 13
File 2 of smart media 23 read by
5 is stored in the image file memory 14 and stored in the DPOF
The file 26 is stored in the DPOF file memory 15.

The controller 20 reads camera information from the image reproduction information 26a in the DPOF file memory 15. When the solid-state imaging device used in the digital camera 22 is a honeycomb CCD, the filtering coefficient represented by Expression 1 is read from the coefficient memory 16 and input to the image processing unit 17.

The image processing unit 17 converts the image data 27a of the image file 25a from the image file memory 14 into RG
The data is read out for each B, filtered by the filtering coefficient represented by the above-described formula 1, and reduced and displayed on the liquid crystal panel 18. Subsequently, the image data 27a of the image file 25b is read out from the image file memory 14 for each of RGB, subjected to a filtering process using the filtering coefficient represented by the above formula 1, and displayed on the liquid crystal panel 18 in a reduced size. Hereinafter, similarly, each of the image data 27a of the image files 25c to 25n is subjected to the filter processing and reduced and displayed on the liquid crystal panel 18.

The user selects an image to be printed from the image data 27a of the image files 25a to 25n reduced (thumbnail display) in a matrix form on the liquid crystal panel 18 by using the operation unit 19, and performs density correction, color correction,
After setting the print size, number of prints, etc., operate the print start key. As a result, after the selected filtered RGB image data is converted into YMC image data by the image processing unit 17,
Each line is transferred to the thermal head of the printing unit 21.

In the printing section 21, yellow, magenta, and cyan images are sequentially recorded in three color planes.
A full-color image is color-recorded on a color thermosensitive recording paper.
After the yellow image is color-recorded, a predetermined ultraviolet ray is irradiated to fix the yellow thermosensitive coloring layer of the color thermosensitive recording paper with light. After the magenta image is color-recorded, a predetermined ultraviolet ray is applied to fix the magenta thermosensitive coloring layer of the color thermosensitive recording paper with light. Further, the cyan thermosensitive coloring layer does not develop a color in a normal storage state, and thus does not have light fixing properties.

When the solid-state image pickup device used in the digital camera 22 is a Bayer type CCD, the controller 20 reads out the filtering coefficient represented by Expression 2 from the coefficient memory 16 and inputs the filtering coefficient to the image processing unit 17. .
The rest is the same as the case of the honeycomb type CCD, and thus the description is omitted.

In the above embodiment, the image processing unit 17
Applied the filtering process to the RGB image data. As shown in FIG. 7, the luminance data (Y data) and the color difference data (CR data, CB data) were obtained from each of the RGB image data.
After performing image processing on each of them, RGB image data may be created from these.
The Y data, CR data, and CB data are represented by the following equations 3, 4, and 5, respectively.

[0032]

(Equation 3)

[0033]

(Equation 4)

[0034]

(Equation 5)

In the present embodiment, the filtering coefficient is changed not only by the type information of the solid-state imaging device but also by the presence / absence information of the low-pass filter. When the solid-state imaging device of the digital camera 22 is a honeycomb CCD and a low-pass filter is used, a filtering coefficient f3 (i, j) represented by the following Expression 6 is applied to CR data and CB data. Is applied, and for Y data, Equation 7
Apply the filtering coefficient f4 (i, j) represented by.

[0036]

(Equation 6)

[0037]

(Equation 7)

When the solid-state imaging device is a Bayer CCD and a low-pass filter is used,
For CR data and CB data, a filtering coefficient f5 (i, j) expressed by the following equation 8 is applied, and for Y data, a filtering coefficient f6 expressed by an equation 9 is applied.
Apply (i, j).

[0039]

(Equation 8)

[0040]

(Equation 9)

When the solid-state image sensor is a honeycomb CCD and a low-pass filter is not used, the following equation 1 is used for CR data and CB data.
Applying a filtering coefficient f7 (i, j) represented by 0,
For Y data, a filtering coefficient f8 (i, j) expressed by Expression 11 is applied.

[0042]

(Equation 10)

[0043]

[Equation 11]

When the solid-state imaging device is a Bayer type CCD and no low-pass filter is used, the following equation 1 is used for CR data and CB data.
Applying a filtering coefficient f9 (i, j) represented by 2
For Y data, a filtering coefficient f10 (i, j) represented by Expression 13 is applied.

[0045]

(Equation 12)

[0046]

(Equation 13)

In the present embodiment, by using the filtering coefficients f7 (i, j) to f10 (i, j), an image photographed by a low-cost digital camera not using a low-pass filter can be displayed on a monitor. When printing is performed or when printing is performed by a printer, false colors and false contour emphasis are reduced to reduce the occurrence of moire and prevent deterioration in image quality.

In the embodiment described above, luminance data (Y data) and color difference data (CR data, CB data)
Were subjected to the filtering process, but may be applied to either one of them. In this case, false contour enhancement can be reduced by performing filter processing on the luminance data, and false color can be reduced by performing filter processing on the color difference data. In addition to the color thermal printer described in the above embodiment, a digital photographic printer having, for example, a laser scanning exposure device and exposing a photosensitive material to record a color image may be used. An ink jet printer for recording an image may be used. Although a liquid crystal panel is used as a monitor, a CRT or a plasma display may be used.

[0049]

As described above in detail, the image processing method according to the present invention uses a plurality of filtering coefficients for filtering to reduce image quality deterioration at the time of printing or monitor display caused by camera information of a digital camera. Since the filtering coefficients are prepared and used in accordance with the camera information, deterioration in image quality of image data obtained by photographing with the digital camera can be reduced. Also,
If information indicating the type of the solid-state imaging device is used as the camera information, optimal filter processing can be performed even when the spatial frequency has direction dependency due to a difference in pixel arrangement, and reduction in print or display image quality is reduced. can do. In addition, if information indicating the presence or absence of a low-pass filter is used as the camera information, optimal filter processing can be performed even on image data obtained by a low-cost digital camera that does not have a low-pass filter, thereby reducing degradation in image quality. Can be. Further, since the image processing includes a filter processing for applying different filtering coefficients to each of the luminance data and the color difference data created from the image data, optimal filter processing is performed for each of false color reduction and false contour enhancement reduction. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a printer that implements an image processing method of the present invention.

FIG. 2 is an explanatory diagram showing a directory structure of a smart media.

FIG. 3 is an explanatory diagram showing a schematic configuration of a Bayer CCD.

FIG. 4 is an explanatory diagram illustrating a schematic configuration of a honeycomb CCD.

FIG. 5 is an explanatory diagram showing a part of image data obtained by photographing with a digital camera using a honeycomb CCD.

FIG. 6 is an explanatory diagram showing a part of image data obtained by photographing with a digital camera using a Bayer-type CCD.

FIG. 7 is a block diagram illustrating an image processing unit according to an embodiment that performs image processing on each of luminance data and color difference data.

[Explanation of symbols]

 Reference Signs List 10 Printer 15 Memory for DPOF file 16 Coefficient memory 17 Image processing unit 21 Printing unit 22 Digital camera 23 Smart media 30 Bayer type CCD 35 Honeycomb type CCD

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 5B057 BA02 CA01 CA08 CA12 CA16 CB01 CB08 CB12 CB16 CC01 CE03 CE06 CH08 5C021 PA36 PA37 PA38 PA51 PA78 PA82 PA83 XB12 XB16 YA01 YA22 YC00 5C077 LL08 LL09 MM03 PP01 PQ08 PQ12 TT09 5C079 HB01 HB04 JA23 LA15 LA31 MA11 NA02 NA04

Claims (4)

[Claims] 1. An image processing method for performing image processing on image data obtained by photographing with a digital camera, wherein a plurality of filtering coefficients for reducing image quality deterioration due to camera information of the digital camera are prepared. An image processing method, wherein a filtering coefficient according to the camera information is selected from the plurality of filtering coefficients and used for the image processing. 2. The image processing method according to claim 1, wherein the camera information is information indicating a type of a solid-state imaging device used in the digital camera. 3. The image processing method according to claim 1, wherein the camera information is information indicating presence / absence of a low-pass filter. 4. The image processing according to claim 1, wherein the image processing includes a filtering process for applying different filtering coefficients to each of luminance data and chrominance data created from the image data. Method.