JP2001144983A - Image data conversion method for ink jet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image data conversion method for an ink jet recorder by which an image providing a similar impression can be obtained even from any of recording media with different color development characteristics by applying luminance gray level conversion to each recording medium depending on its characteristic. SOLUTION: This method includes a step 1 where the gray level of an image is converted into a luminance signal that is normalized into a value between 0 and 1 on the basis of an expression of luminance signal=10(-gray level)×255, a step 2 where the luminance signal between a maximum luminance signal and a minimum luminance signal is divided into 256 divisions according to a prescribed characteristic, a step 3 where each of 256 divisions of the luminance signals is converted into a gray level on the basis of an expression gray level signal = -Log10 (luminance signal/255), and a step 4 where the gray level signals are normalized into integers of 0 to 255. Using a conversion curve obtained in this way depending on the characteristic of each recording medium can make conversion between the luminance signal and the gray level signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data conversion method for an ink jet recording apparatus, and more particularly, to an image data conversion method for various kinds of recording media used for ink jet recording.

[0002]

2. Description of the Related Art Heretofore, as a recording apparatus of this type, a host apparatus which transfers recording data to the recording apparatus, receives recording data from the host apparatus, and applies a plurality of color inks to a recording surface in accordance with the data. 2. Description of the Related Art There is a system including a color ink jet recording apparatus that performs recording by adhering.

In a host device in these systems, image data is handled by three primary colors of RGB in order to perform interactive processing by a display device, while in an ink jet printing device, printing is performed by four colors of CMYK inks. It is common to do. In such a system, it is necessary to perform correction / conversion processing from RGB values depending on the display device to CMYK values depending on the recording device.

FIG. 1 is a process chart for performing a general correction / conversion process from RGB values to CMYK values.

First, the characteristics of the display device are corrected by input gamma correction (S1) so that the luminance value on the display is proportional to the input value. next,
In the brightness / density conversion (S2), the RGB brightness signals are converted into CMY density signals. Next, in color correction (S3), unnecessary components of the ink used in the inkjet recording apparatus are corrected,
Reproduce faithful colors. Next, UCR / black generation (S4)
Then, under color removal is performed with a predetermined value, a predetermined amount of black data is generated, and CMYK data that can be recorded by a printer from the CMY data can be obtained.
To the color data. Next, output gamma correction (S5)
Then, the output values are converted so that the density on the recording medium is proportional to the input values for the input values of the respective colors CMYK.
Finally, the quantization (S6) converts the multi-valued signal into a binary signal that can be expressed by a printer.

In the input gamma correction (S1), correction is performed according to the input gamma value selected and designated by the user and the type of display, and in the luminance / density conversion (S2),
The conversion is performed by the input source selected and specified by the user, and in the quantization (S6), a predetermined conversion is performed by the quantization method selected and specified by the user. In addition, color correction (S
3), UCR / black generation (S4), output gamma correction (S4)
In 5), a predetermined conversion process is performed according to a combination of the type of recording medium selected and designated by the user and the quantization method.

[0007]

However, in the above-mentioned conventional example, although the output density range differs for each recording medium, all the recording media are selected as shown in FIG. Since the same luminance / density conversion was performed by the input source, the gradation characteristics of the density on each recording medium were the same, but the absolute value of the density was different for each recording medium as shown in FIG. The gradation characteristic when the density data was converted into a luminance signal was different for each recording medium as shown in FIG. In order to clarify the difference in the gradation characteristics, FIG. 5 shows a normalized gradation characteristic of each recording medium shown in FIG. Here, in FIGS. 2, 3, 4, and 5, the following three types of recording media are used as examples.

Recording medium A: minimum density of 0.05, maximum density of 2.0 Recording medium B: minimum density of 0.05, maximum density of 1.5 Recording medium C; minimum density of 0.05, maximum density As described above, when an image expressed linearly in luminance on a display is recorded on each recording medium having a different density region capable of being expressed, the gradation characteristics of the density expressed on the recording medium are changed. When converted into luminance gradation characteristics, there is a problem that an image having a different atmosphere is output for each recording medium because the characteristics are different for each recording medium.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and an object of the present invention is to perform luminance-density conversion in accordance with the characteristics of each recording medium so that any recording medium having different coloring characteristics can be obtained. It is an object of the present invention to provide an image data conversion method for an ink jet recording apparatus capable of obtaining an image giving a similar impression on a recording medium.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for recording an image represented linearly on a display on recording media having different density regions capable of being represented. In an image data conversion method for an ink jet printing apparatus for converting a gradation characteristic of density expressed on the recording medium into a gradation characteristic of luminance, a luminance / density conversion having different characteristics for each recording medium is performed. It is assumed that.

That is, the gradation characteristics when the density expressed on the recording medium is converted into a luminance signal and normalized are unique to each recording medium so that the same characteristic can be expressed in each recording medium. It is characterized in that RGB luminance signals are converted into CMY density signals in accordance with the values of the minimum density and the maximum density. Here, the minimum density (R, G, B) = (25
5, 255, 255) (expressing white) on the recording medium, and the maximum density is (R, G, B) = (0,
(0, 0) indicates the density on the recording medium recorded at the time (expressing black).

According to the image data conversion method of the ink jet recording apparatus of the present invention, by performing luminance density conversion according to the characteristics of each recording medium, an image giving the same impression on any recording medium having different coloring characteristics can be obtained. It is possible to obtain

[0013]

Embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 6 is a diagram showing conversion from RGB signals to CMY signals in each recording medium, and is a diagram which best illustrates the features of the present invention. It represents the characteristic of converting an 8-bit RGB signal of each color into an 8-bit CMY signal of each color, and indicates that different conversions are performed on different recording media. In FIG. 6, a recording medium A has a maximum density of 2.0 and a minimum density of 0.05, a recording medium B has a maximum density of 1.5 and a minimum density of 0.05, and a recording medium. C is a recording medium having a maximum density of 1.0 and a minimum density of 0.05, and is a conversion curve of luminance / density conversion for converting 0 to 255 RGB input signals into 0 to 255 CMY output signals. Is represented. As can be seen from FIG. 6, depending on the type of the recording medium, the luminance / density conversion can be performed using the conversion curve according to the characteristics.

These conversion curves are generated by the following procedure.

Procedure 1: The density value is converted into a luminance signal normalized to 0 to 1 by the following equation (1).

[0017]

[Outside 2]

Step 2: The space between the maximum luminance signal and the minimum luminance signal is divided into 256 parts according to predetermined characteristics.

Procedure 3: The 256-divided luminance signal is converted into a density value by the following equation (2).

Density signal = −LOG ₁₀ (luminance signal / 255) (2) Step 4: Normalize the density signal to an integer of 0 to 255.

Hereinafter, the generation of the conversion curve of the luminance / density conversion for the above three types of recording media will be described.

According to the procedure 1, the luminance signals of the recording media A, B, and C are as follows from the equation (1). Here, the value is rounded off to the fourth decimal place.

Minimum luminance signal Maximum luminance signal Recording medium A 2.55 227.269 Recording medium B 8.063 227.269 Recording medium C 25.5 227.269 By this conversion, the range of luminance in each recording medium becomes zero. ~ 25
5, the gradation characteristic can be represented by a curve having a predetermined characteristic within this luminance range. Next, FIG. 7 shows an input signal equivalent to a predetermined characteristic (in this case, a linear luminance) in an input signal equally divided into 256 from 0 to 255 by the procedure 2. As shown in FIG. 7, each recording medium has a luminance linear characteristic with respect to an input in each luminance range. Here, as an example, a luminance linear characteristic like the gradation characteristic A in FIG. 8 is used, but a characteristic shown as the gradation characteristic B may be used.

Next, FIG. 9 shows values obtained by the equation (2) for each value divided into 256 according to the procedure 3. As shown in FIG. 9, the characteristics with respect to the density represent almost the same density in a bright portion, and the darker one has a higher maximum density, and the lower one has a lower density. It shows the characteristic that rises.

Finally, according to procedure 4, the density signal is set to 0 to 2
FIG. 6 shows the result normalized to an integer value of 55. In FIG. 6, the horizontal axis represents the RGB luminance signal, and the vertical axis represents the CMY density signal, and shows a conversion curve of the luminance / density conversion showing how the CMY is output with respect to the RGB input.

By using the conversion curve of the luminance / density conversion obtained by the above procedure, the same characteristic can be represented as the luminance gradation characteristic in the density range that can be expressed by each recording medium. As a result, it is possible to obtain an image giving a similar impression between the recording media.

(Embodiment 2) Normally, the recording medium that can be selected by the user is a generic term such as glossy paper, coated paper, plain paper, and the like. Image signal processing is performed according to the recording medium recommended by the manufacturer. Therefore, if the characteristics of the recording medium used are different from those recommended by the manufacturer, a different impression is output for each recording medium.

Therefore, in order to obtain a good image on the recording medium used by the user, the maximum density and the minimum density of the paper type used by the user are specified, and the conversion curve of the brightness density conversion is specified based on the data. Generate By registering this data in the printer driver, it is possible to obtain a good image on the paper type that the user always uses.

As a method of obtaining the maximum density and the minimum density,
A pattern prepared in advance is recorded on a recording medium that is normally used, and data is captured by image input means such as a scanner. Then, based on the value, a conversion curve of the luminance / density conversion is generated according to the above-described procedure, and registered in the printer driver.

By doing so, it is possible to obtain an image that gives a similar impression between the recording media that the user always uses.

(Embodiment 3) The density of the recording medium does not differ as much as the maximum density of each recording medium. For example, if the maximum density is the same even if there is a difference between 0 and 0.1, the luminance density conversion Are almost the same as shown in FIG. Here, the recording media D, E, F, and G are the following recording media.

Recording medium D: minimum density of 0.1, maximum density of 2.0 Recording medium E: minimum density of 0.0, maximum density of 2.0 Recording medium F; minimum density of 0.1, maximum density Is 1.0 recording medium G; the minimum density is 0.0 and the maximum density is 1.0. Therefore, the minimum density of each recording medium is fixed to a predetermined value.
Even when the conversion curve of the brightness / density conversion is determined based on the value of the maximum density, it is possible to obtain an image giving a similar impression on each recording medium.

By determining the conversion curve of the brightness / density conversion based on only the maximum density value in this way, the number of combinations is smaller than that determined from the maximum density value and the minimum density value, so that the storage capacity is reduced. For example, assuming that a conversion curve for a predetermined maximum density and minimum density value is held, if the type of the maximum density value is N and the type of the minimum density value is M, the conversion curve is only the maximum density. The method of determining N has N types of conversion curves, and the method of determining the conversion curves from the values of the maximum density and the minimum density requires N × M types of conversion curves.

[0034]

As described above, according to the present invention, the gradation characteristics obtained when the density represented on the recording medium is converted into a luminance signal and normalized are similar in each recording medium. Is converted from an RGB luminance signal to a CMY density signal in accordance with the minimum density and maximum density values unique to each recording medium. Is performed, it is possible to obtain an image giving the same impression on any recording medium having different coloring characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a flow of a conversion process from an RGB signal to a CMYK binary signal.

FIG. 2 is a diagram illustrating conversion from an RGB signal to a CMY signal.

FIG. 3 is a diagram illustrating a density characteristic from black to white in each recording medium.

FIG. 4 is a diagram illustrating luminance characteristics from black to white in each recording medium.

FIG. 5 is a diagram in which luminance characteristics from black to white in each recording medium are normalized.

FIG. 6 is a diagram illustrating conversion from RGB signals to CMY signals in each recording medium.

FIG. 7 is a diagram illustrating a luminance characteristic from black to white in each recording medium.

FIG. 8 is a diagram illustrating a density characteristic from black to white in each recording medium.

FIG. 9 is a diagram illustrating conversion from RGB signals to CMY signals in each recording medium.

FIG. 10 is a diagram showing gradation characteristics of a display.

Continued on the front page F-term (reference) 2C056 EB27 EB42 EC76 EC79 2C057 AF39 AL36 AL37 CA10 5C074 BB16 DD02 DD23 DD27 EE08 FF15 HH04 HH08 5C077 LL19 MP08 PP15 PP32 PP33 PP37 PP43 SS06 TT05 5C079 HB01 KA03 PA13 LA15

Claims (8)

[Claims] When recording an image expressed linearly on a display on recording media having different densities that can be expressed on a display, a gradation characteristic of the density expressed on the recording medium is represented by a luminance gradation. An image data conversion method for an ink-jet recording apparatus for converting into tone characteristics, wherein brightness-density conversion having different characteristics for each recording medium is performed. 2. The image data conversion method according to claim 1, wherein the luminance density conversion is performed based on the maximum density and the minimum density that can be expressed on the recording medium. 3. A method for reading an image, comprising: means for reading an image, wherein 100% black data ((RGB) = (0,0,
The image data conversion method according to claim 2, wherein the maximum density and the minimum density of the recording medium are obtained by reading the data (0) and the density of the recording medium. 4. The image data conversion method according to claim 1, wherein the luminance density conversion is performed based on a maximum density value that can be expressed on the recording medium. 5. A method for reading an image, wherein 100% black data ((RGB) = (0,0,
The method according to claim 4, wherein the maximum density of the recording medium is obtained by reading the density of the data (0). 6. The image data conversion method according to claim 1, further comprising a conversion table having different characteristics for each of the printing media, and performing the brightness / density conversion by the table conversion. 7. The image data conversion method for an ink jet printing apparatus according to claim 6, comprising a maximum density value and a minimum density value of the recording medium, and generating a conversion table from the values. 8. An image data conversion method for an ink-jet printing apparatus for performing brightness-density conversion using a conversion curve according to the characteristics of a printing medium according to the type of printing medium. , A procedure for converting the density value into a luminance signal normalized to 0 to 1, a procedure for dividing the maximum luminance signal and the minimum luminance signal into 256 according to a predetermined characteristic, and a density signal = −LOG ₁₀ (Luminance signal / 255)
An image data conversion method for an ink jet recording apparatus, wherein a conversion curve is generated by a procedure for converting a 256-divided luminance signal into a density value and a procedure for normalizing the density signal to an integer of 0 to 255.