JP2000113172A - Image processing system and method - Google Patents

Abstract

(57) [Problem] In color caching in which color matching is performed using a cache table, it is rather slow for color processing of a complicated image. If the pixel value of an image input from an image input device is equal to or less than a predetermined value in step S317, conversion is performed in step S318 so that lower bits are discarded. Then, in step S321, the cache table is searched using the pixel values after the conversion, so that efficient color matching processing can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method for digital color image data, and is particularly effective for improving the processing speed when a photographic image described by color signals suitable for display on a display is output to a printer. is there.

[0002]

2. Description of the Related Art In recent years, with the advancement of the performance of host computers, a so-called color matching system (hereinafter referred to as CMS) which performs color matching processing between an image data input device and an output device in a multimedia system centered on the host computer. Notation) has been put to practical use.

[0003] For example, ColorSyn of Apple Inc.
In the CMS represented by c, conversion of a color signal from a color space dependent on an input device (Device Dependent Color Space) to a color space independent of a device (Independent Color Space), or a color space independent of a device. Conversion to a color space depending on the output device can be easily performed, and a CMS common to the system is realized.

In such a system, a profile, which is data representing the color conversion characteristics of each device, is prepared in the host computer in order to realize color matching. Then, color space conversion is performed according to the conversion characteristics of the profile automatically or manually selected at the time of conversion. Further, the CMS enables color signal processing, correction, and conversion in a color space independent of the device.

[0005] The arithmetic processing of the color signal accompanying the color space conversion generally involves complicated processing such as non-linear operation, lookup table reference and interpolation as shown in JP-A-7-193723. For this reason, Japanese Patent Application Laid-Open No. 8-279030
Has proposed a color caching process as described below.

That is, the color signal values before and after the conversion once calculated are related and stored in an area called a cache table. In the subsequent conversion process, if the color signal value to be converted at that time is registered in the cache table, the color signal value is stored in the cache table in place of the color space conversion calculation process for the color signal value. The other signal value stored in association with the value is determined as the converted color signal value.

[0007]

With the spread of image input devices such as digital cameras and inexpensive large-capacity storage devices such as CD-ROMs in recent years, images to be subjected to CMS include photographic images, Complex images that are rich in changes at the pixel level are increasing.

However, the above-described conventional color caching processing does not effectively work on such complicated image color processing. Rather, color matching processing can be performed at a higher speed without color caching. is there.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to provide an image processing system and a method thereof that enable high-speed color matching processing by color caching.

[0010]

According to one aspect of the present invention, an image processing method includes the following steps.

That is, an image processing method in an image processing system including an image input device and an image output device,
An input step of inputting an image from the image input device, a determining step of determining whether a pixel value of the input image is equal to or less than a predetermined value, and a pixel whose pixel value is determined to be equal to or less than a predetermined value in the determining step A lower bit conversion step of converting the lower bits of the table, a table conversion step of converting the pixels whose lower bits have been converted based on the table, and an output of outputting the pixels converted by the table conversion step to the image output device. And a step.

For example, in the lower bit conversion step, a predetermined number of lower bits of a pixel whose pixel value is determined to be equal to or smaller than a predetermined value in the determination step is replaced with 0.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <Principle of the Present Invention> First, the principle of the present invention will be briefly described.

Generally, a color signal value given to an image output device such as a printer is represented by each color component (hereinafter referred to as “element”).
) Is mainly represented by 8 bits or 16 bits. However, in most image output devices, even if, for example, data of 8 bits, that is, 256 gradations is provided for one element, an actual output can be output only at gradations several bits lower than 8 bits.

Many of the images (conversion source images) given to the printer are described with signal values suitable for an image display device (display). The characteristics of a display such as a CRT are expressed by the following equation (1) using a constant γx as the relationship between each element Sx (maximum value Smax) of the color signal value and the output luminance Yx. Note that "に お い て"
Indicates the factorial.

Yx = (Sx / Smax) ^ γx (1) According to the equation (1), it can be seen that the chrominance signal is not uniformly allocated to the luminance, that is, it has a nonlinear characteristic. . Generally, γx is a value of about 1.4 to 2.2, and the larger the element value, the larger the change rate of luminance. Therefore, in a portion where the change rate of the luminance is small, that is, in a portion where the element value is small, it is considered that even if the lower one or two bits of the element value are changed, the output luminance is hardly affected.

Therefore, in an image in which the lower bits of elements having a small change in the measured value (for example, luminance) are truncated to zero, the possibility of the appearance of the same color signal increases, and the effect of color caching increases.

Therefore, the inventor prepares a general photographic image and an image which has been subjected to a process of truncating lower-order bits for an element value less than a certain value with respect to the photographic image. An experiment was conducted in which CMS by color caching was performed using an input device and a color printer as an output device. As a result, although there was a difference depending on the original image, the processing time was shortened by 4 to 13%, and there was almost no difference in the output from the color printer.

The present invention has been made based on the above points. Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

<Image Processing System Configuration> FIG. 1 is a block diagram showing the configuration of an image processing system according to the present embodiment. This system mainly includes a camera 111 as an input device.
A scanner 112, a host computer 10 for performing editing processing and color matching processing, and a monitor 12 as an output device.
And a printer 13. Here, the host computer 10 can be replaced with dedicated hardware that realizes the same operation.

The camera 111 is an input device for inputting a captured image, such as a digital camera or a video camera. The scanner 112 is an input device for reading and inputting a document image, such as a flatbed scanner or a film scanner. The monitor 12 is a display such as a CRT or a liquid crystal, and is a display device that displays an image and also displays information necessary for a user to make an input to the system or to confirm a system operation. The printer 13 is an output device that forms an image on a recording medium using a recording material.

The external storage device 14 is composed of a storage medium such as a hard disk, a magneto-optical disk or a floppy disk and a drive which is a read / write device for them.
The image data supplied from the scanner 1 or the scanner 112 can be stored, a color matching process or an editing process can be performed on the stored image data, and the processed image data can be stored again. Further, the stored image can be displayed on the monitor 12 or supplied to the printer 13 and printed on a recording paper or the like as needed.

The external storage device 14 also stores a profile for each device required for color matching processing, and the host computer 10 reads the profile as necessary, and performs color matching between an input device and an output device. Processing can be performed.

Normally, a control program for realizing image processing in the present embodiment is executed by the host computer 10.
The control program is stored in the ROM (not shown) or the like, but it is also possible to store the control program in the external storage device 14. In this case, the host computer 10 reads the program stored in the external storage device 14 into the host computer 10 in accordance with a user's instruction, and executes the program, thereby realizing the image processing of the present embodiment.

The keyboard 15 and the mouse 16 are operated by the user as required, and can input predetermined instructions to the host computer 10.

FIG. 2 shows an example of the detailed configuration of the host computer 10. In the figure, reference numeral 21 denotes a console, which comprises the keyboard 15, mouse 16, monitor 12, and the like shown in FIG.
It is connected to PU17.

The CPU 17 has a system control section 171 for controlling the entire system, an arithmetic processing section 172 for executing various arithmetic operations, and a working memory 173 called a register for storing data necessary for the arithmetic operation as needed. . The CPU 17 performs a color matching process on the image data read in the host computer 10 and stored in the RAM 19 based on a program stored in the ROM 18 or the RAM 19, and an output device (the monitor 12 or the printer 13). Output to

The video RAM 23 stores a screen to be displayed on the monitor 12.

<Explanation of Profile> Possible combinations of input devices and output devices in the present system are as follows.

(1) Camera 111-Monitor 12 (2) Camera 111-Printer 13 (3) Scanner 112-Monitor 12 (4) Scanner 112-Printer 13 (5) Monitor 12-Printer 13 (6) Printer 13-Monitor 12. Here, the combination of (6) indicates a so-called preview process, in which an image that will be output by the printer 13 is displayed on the monitor 12 in advance, and the user confirms the image.

In the present embodiment, it is necessary to perform different color matching processing for each of such combinations. When executing the color matching processing of the present embodiment, the CPU 17 reads an input profile corresponding to the input device and an output profile corresponding to the output device from the external storage device 14.

Here, the profile stores data indicating the relationship between device-dependent color signals and device-independent color signals. That is, the input profile stores data for converting an input device-dependent color signal into a device-independent color signal. On the other hand, the output profile stores data for converting a device-independent color signal into an output device-dependent color signal. Note that the output profile may be data including a process (color space compression) of converting a color signal of input image data into a color signal within a color reproduction range of the output device.

That is, the CPU 17 reads the input profile corresponding to the input device and the output profile corresponding to the output device from the external storage device 14 and converts the input device-dependent color signal into a device-independent color signal such as the CIELAB color system. Through the output device, the color signal is converted into an output device-dependent color signal. For example, in the case of the combination of the above (2), by referring to the profile of the camera 111 and the profile of the printer 13, the RGB color signals input from the camera 111 are once converted into the CIELAB format, and then the CIELA
CMY capable of outputting B-format signals in the printer 13
Convert to format.

The profile in this embodiment is as follows:
InterColor Profile Format (InterColor
Profile Format).

<Color Matching Process> FIG. 3 is a flowchart showing the color matching process in this embodiment. As described above, the processing shown in the flowchart is stored in the ROM 18 as a control program, and is read and executed by the CPU 17.

First, original image data to be processed is selected (S310), and an area for storing the processed image data is secured in the external storage device 14 (S311).
Similarly, an area for storing the cache table is secured (S312). Then, a profile corresponding to the input device and a profile corresponding to the output device are selected from the external storage device 14 (S313).

Then, the unprocessed pixel in the original image data is set to 1
After the selection (S314), the color signal of the selected pixel is read (S315), and an unprocessed element is selected from the read color signal (S316). If the element value is smaller than the predetermined constant (S317), a value in which all lower bits of the predetermined number of digits are set to 0 in the element is calculated (S318), and the element is rewritten with the calculated value (S318).
319). If there is an unprocessed element in the color signal (S320), the process returns to step S316.

In step S320, if the processing of all the elements has been completed for the color signal, the cache table is searched for the value of the color signal (S321), and the value (each element value) of the color signal is stored in the cache table. Is determined as a first color signal value (input value) (S322). If registered, the second color signal value (output value) stored in the cache table in association with the first color signal value in order to use the converted color signal value (output color signal value). ) Is read (S323), and the process proceeds to step S327.

On the other hand, if the value of the color signal is not registered in step S322, the input color signal value (element value) is determined based on the profile selected in step S313.
Then, an output color signal value is calculated (S324). Then, after securing or searching for an area for storing a new color signal value in the cache table (S325), step S31 is performed.
The element value calculated in step 8 is used as the first color signal value,
The value calculated in 324 is stored in the area as a second color signal value (S326). Note that the first color signal value newly stored in the cache table is set in step S318.
If not calculated in step S315, step S315
The color signal value read out in step (1) may be used.

The process proceeds to step S327, and in the area for storing the processed image data secured in step S311, a pixel position which is the same as the pixel selected in step S314 in image space is determined. Then, the output color signal read in step S323 or the output color signal value calculated in step S324 is written in the pixel position (S328).

After setting the pixel as a processed pixel (S
329), it is determined whether or not processing has been completed for all pixels in the original image data (S330). If there is an unprocessed pixel, the process returns to step S314, and processing for the next pixel is continued.

If the processing has been completed for all pixels, the processed image data is transmitted to the output device desired by the user, that is, the monitor 12 or the printer 13 (S33).
1).

The predetermined constant in step S317 and the predetermined number of digits in step S318 may be fixed values in the system, or may be input by the user using the console 21. Also, it may be described in any of the input and output profiles.

Further, in the present embodiment, an example has been described in which the lower-order bit of a pixel whose pixel value is equal to or less than a predetermined value is replaced with 0, but the threshold value of this pixel value is not limited to one value. . For example, two thresholds may be prepared, and the number of digits of the lower bit to be converted may be determined for each.

As described above, according to the present embodiment,
By converting the element values of the color signal to a level that does not cause a problem in practical use, the possibility that the same color signal appears in the image can be increased. Therefore, since the color caching for performing the color conversion using the cache table is more effectively executed, the processing speed of the color matching between the input device and the output device can be increased.

[0046]

[Other Embodiments] Even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus (for example, a copying machine) Machine, facsimile machine, etc.).

Another object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or apparatus, and to provide a computer (or CPU) of the system or apparatus.
And MPU) read and execute the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD
-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the OS (Operating System) running on the computer based on the instruction of the program code. ) May perform some or all of the actual processing, and the processing may realize the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instruction of the program code, It goes without saying that the CPU included in the function expansion board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the flowcharts described above.

[0053]

As described above, according to the present invention, the likelihood of appearance of the same color signal in an image is increased without actually changing the color appearance of the image, and color caching works effectively. An image processing method can be provided.

[0054]

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image processing system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed configuration of a host computer 10.

FIG. 3 is a flowchart illustrating a color matching process according to the embodiment.

[Explanation of symbols]

 111 Camera 112 Scanner 12 Monitor 13 Printer 14 External Storage Device 15 Keyboard 16 Mouse 17 CPU 18 ROM 19 RAM 21 Console 22 Input / Output Interface 23 Video RAM

Continued on the front page F-term (reference) 5B050 AA10 BA07 BA10 BA13 BA18 CA09 DA02 DA04 EA09 FA03 FA05 FA19 5C077 LL18 MM03 MP08 PP31 PP39 PP41 PP43 PP54 PQ08 PQ12 PQ22 PQ23 SS02 TT02 5C079 HA13 HA19 HB01 MA0211 MA11 MA17 MA20 NA03 NA11 NA17 PA03 PA05

Claims (13)

[Claims] 1. An image processing method in an image processing system including an image input device and an image output device, comprising: an input step of inputting an image from the image input device; and a pixel value of the input image being equal to or less than a predetermined value. A determination step of determining whether there is a pixel, a lower bit conversion step of converting lower bits of a pixel whose pixel value is determined to be equal to or less than a predetermined value in the determination step, and An image processing method, comprising: a table conversion step of performing a conversion by a table conversion step; and an output step of outputting pixels converted by the table conversion step to the image output device. 2. The method according to claim 1, wherein, in the lower bit conversion step, lower bits of a predetermined number of digits of a pixel whose pixel value is determined to be equal to or smaller than a predetermined value in the determination step are replaced with 0. Image processing method. 3. The image processing method according to claim 1, wherein in the table conversion step, color matching between the image input device and the image output device is performed. 4. The image processing method according to claim 3, wherein said table is a cache table. 5. A calculating step of calculating a color conversion output value for a pixel converted by the lower bit conversion step based on characteristic information of the image input device and the image output device stored in a memory; 2. The image processing method according to claim 1, further comprising: storing the color conversion output value calculated in the calculation step in the table in association with the pixel converted in the lower bit conversion step. 6. The image processing apparatus according to claim 5, wherein the calculating step and the storing step are performed when the pixel converted by the lower bit converting step is not stored in the table. 7. The image processing method according to claim 5, wherein said characteristic information is profile information. 8. The image processing method according to claim 7, wherein the predetermined number is included in the profile information. 9. The image processing method according to claim 7, wherein the predetermined number of digits is included in the profile information. 10. The image processing method according to claim 1, wherein in the inputting step, an RGB signal is input. 11. The image processing method according to claim 1, wherein the profile has a structure conforming to an intercolor profile format. 12. An image processing system comprising an image input device and an image output device, comprising: input means for inputting an image from the image input device; and determining whether a pixel value of the input image is equal to or less than a predetermined value. Determining means for performing conversion; lower-bit conversion means for converting lower bits of a pixel whose pixel value is determined to be equal to or less than a predetermined value in the determining step; and a table for converting the pixel whose lower bit has been converted based on the table. An image processing system comprising: a conversion unit; and an output unit that outputs a pixel converted by the table conversion unit to an image output device. 13. A recording medium in which a program code for image processing in an image processing system including an image input device and an image output device is recorded, wherein the program code is an input step of inputting an image from the image input device. And a code of a determining step of determining whether the pixel value of the input image is equal to or less than a predetermined value; and a lower order converting a lower bit of the pixel whose pixel value is determined to be equal to or less than the predetermined value in the determining step. A code for a bit conversion step, a code for a table conversion step for converting the pixels whose lower-order bits have been converted based on a table, and a code for an output step for outputting the pixels converted by the table conversion step to the image output device And a recording medium comprising: