JPH06152953A - Image reader - Google Patents

Abstract

(57) [Summary] [Purpose] The same orange-based image as the film original is read to perform shading correction on the film original to obtain an image signal whose color balance is always stable. When the outer frame base film area 14b of the film original 14 reaches the reading position, read data for a plurality of lines is taken in, averaged at each pixel of the CCD 38, and is stored in the memory 40 as shading correction data.
Store in b. Then, the image area 1 of the film original 14
When 4a reaches the reading position, the shading correction data is read and the shading correction calculation circuit 40 is read.
By being transferred to a, the shading correction calculation circuit 40a corrects the image area 14a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is directed to film originals, especially 3
The present invention relates to an image reading device for reading a 5 mm negative strip film, for example, an image reading device suitable for a digital copying machine, a film scanner, an electronic file device, a facsimile and the like.

[0002]

2. Description of the Related Art Generally, in an image reading apparatus of this type, shading correction is performed according to variations in pixels of an image sensor such as a CCD (charge coupled device), uneven light amount of a document illumination lamp, and characteristic error of an optical system. Is done,
For example, in a digital copying machine, a reference white color is read in advance as a standard image (shading correction data), and the reading level of an actual document is corrected based on this shading correction data.

On the other hand, in a conventional image reading apparatus that reads a film original by projecting it with a slide projector (SPU), an orange base film of a standard film (for example, ASA100) of each film manufacturer is used as a standard image (shading correction data). The reading level is read in advance and the reading level of the actual film original is corrected based on the shading correction data.

The operation of the conventional example will be described with reference to FIGS. 12 and 13. First, in the setup process, when the SPU mode is set (step 101), the power of the SPU is turned on and the SPU is initialized. The load is set to the initial state (step 102).

In the subsequent negative / positive select process, it is determined whether the positive mode or the negative mode is set (step 103), and the color filter corresponding to the set mode is set (step 104 or 106). And
When the positive mode is set, the user does not set anything on the running body of the film original (step 105), and when the negative mode is set, sets a reference orange base film on the running body of the film original (step 105). 1
07).

In the subsequent shading data collect process, the running body of the film original is moved to the reading position, and the CCD is moved to the projection position from the SPU (step 108). Then, the lamp is turned on with the initial light amount value (step 109), and the light amount is corrected (step 110).
The data read by the CCD is stored as shading correction data (step 111), the lamp is turned off, and the traveling body is returned to the home position (HP) (step 112).

After that, when the user sets the film original on the running body (step 113), the lamp is turned on to prescan the film original (step 114), and after correcting the light amount (step 115), the film original is set. Scanning is performed at a speed according to the magnification, and the read data is corrected with the shading correction data (step 11).
6).

When scanning the same film original, the main scanning in steps 115 and 116 is repeated, and when different originals of the same type are read, the process returns to step 114 and prescan is performed (step 118). When reading a different type of original, the process returns from step 119 to step 103 to store the shading correction data again.

Further, in another conventional image reading apparatus,
For example, as described in Japanese Patent Laid-Open No. 1-94763, the shading correction data that has been read once is stored in another memory so that it can be read again, or the characteristic-specific data of the film is stored in another memory in advance so that the shading correction It is configured to reduce the number of operations for obtaining data.

[0010]

By the way, when the shading correction data is obtained from the negative film, the area on the film where the light is most transmitted, that is, the orange base area which is the unexposed area is read, and the color of the negative film is also read. However, the standard negative film for obtaining the shading correction data is ideally the same as that of the film original because it varies slightly depending on the manufacturer of the film, the type (ASA sensitivity) and the developing conditions.

Therefore, when the standard negative film and the film original are the same, the balance of the respective color signals after correction, that is, the color balance does not largely deviate between different film makers, but the standard negative film different from the film original. There is a problem that the color balance is deteriorated when the orange original area is read and the film original is subjected to the shading correction.

When the shading-corrected original image is .gamma.-converted and output by a copying machine or printer, the color tone varies greatly depending on the film, so that the adjustment requires a great deal of labor.

Here, a method is known in which an unexposed area of a film original is used as shading correction data. However, this method cannot be adopted when there is no unexposed area in the film original.

Further, in the apparatus disclosed in Japanese Patent Laid-Open No. 1-94763, the shading correction data once read is stored in another memory so that it can be read again.
Even if the characteristic data of the film is stored in another memory in advance and used, the new film cannot be dealt with.

In view of the above conventional problems, the present invention provides an image reading apparatus capable of reading the same orange-based image as a film original and correcting the shading of the film original to obtain an image signal whose color balance is always stable. The purpose is to do.

[0016]

In order to achieve the above object, a first means is a projection means for projecting a negative film original, an image sensor for reading an original image projected by the projection means, and the image sensor. Shading correction data is generated from A / D conversion means for converting the image signal read by the device into a multi-valued digital signal and the image signal of the outer frame base region of the negative film original read by the image sensor. Shading correction means for correcting the image signal of the image area of the negative film original with the shading correction data.

A second means is that the shading correction means of the first means averages the image signals in the pixels of a plurality of lines of the outer frame base region of the negative film original read by the image sensor. It is characterized in that data for shading correction is generated.

The third means is projection means for projecting a negative film original, an image sensor for reading the original image projected by the projection means, and an image signal read by the image sensor into a multi-valued digital signal. Shading correction data is generated from the A / D converting means for converting and the image signal of the reference negative orange base film read by the image sensor, and the level ratio of the image signal of each color in the outer frame base region of the negative film original is generated. The present invention is characterized by including shading correction means for detecting a coefficient of the shading correction data and correcting the image signal of the image area of the negative film original with the shading correction data and the coefficient.

A fourth means is a projection means for projecting a negative film original, a color correction filter for correcting the color sensitivity balance of the original image projected by the projection means, and an original image corrected by the color correction filter. And an A / D conversion means for converting an image signal read by the image sensor into a multi-valued digital signal, and a spectral characteristic of a reference negative orange base film, instead of the color correction filter. Shading correction data is generated from the image signal read by the image sensor through the arranged shading correction filter, and the shading correction is performed from the level ratio of the image signal of each color in the outer frame base region of the negative film original. Of the image data of the negative film original is detected and the coefficient of the data for Characterized by comprising a shading correction means for correcting by the coefficient shading correction data.

A fifth means is that the shading correction means of the third or fourth means outputs the image signal of each color in each pixel of a plurality of lines of the outer frame base region of the negative film original read by the image sensor. It is characterized in that the coefficient of the shading correction data is calculated by averaging.

[0021]

In the first means, the shading correction data is generated from the image signal of the outer frame base area of the negative film original, and the image signal of the image area of the negative film original is corrected by the shading correction data. The same orange-based image as the film original can be read to perform shading correction on the film original, and thus an image signal whose color balance is always stable can be obtained.

In the second means, the shading correction data is generated by averaging the image signals in the pixels of a plurality of lines in the outer frame base area, so that accurate shading correction data can be generated. Therefore, it is possible to obtain an image signal whose color balance is always stable.

In the third means, the shading correction data is generated from the image signal of the reference negative orange base film, and the coefficient of the shading correction data is calculated from the level ratio of the image signal of each color in the outer frame base area of the negative film original. Is detected and the image signal in the image area of the negative film original is corrected by the shading correction data and the coefficient, the same orange base image as the film original can be read to perform the shading correction on the film original. It is possible to obtain an image signal whose color balance is always stable.

In the fourth means, the reference negative orange base film has the spectral characteristics, the light is transmitted through a shading correction filter arranged in place of the color filter, and shading is performed from the image signal read by the image sensor. The correction data is generated, the coefficient of the shading correction data is detected from the level ratio of the image signal of each color in the outer frame base area of the negative film original, and the image signal of the image area of the negative film original is used for the shading correction. Since the correction is made using the data and the coefficient, the same orange base image as the film original can be read to perform the shading correction on the film original, and thus an image signal with a stable color balance can be obtained.

In the fifth means, the coefficient of the shading correction data is calculated by averaging the image signals of the respective colors in the pixels of the plurality of lines in the outer frame base area of the negative film original, so that the accurate shading correction data can be obtained. Data can be generated, and thus an image signal whose color balance is always stable can be obtained.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing an embodiment of an image reading apparatus according to the present invention, FIG. 2 is a block diagram showing the image reading apparatus of FIG. 1, FIG. 3 is a perspective view showing the slide projector of FIG. 2 in detail, and FIG. 2 is a perspective view showing in detail the light quantity correcting means shown in FIGS. 2 and 3, FIG. 5 is a block diagram showing in detail the configuration and operation of the peak hold circuit shown in FIG. 1, and FIG. 6 is an explanatory view showing a film original. 7 is a block diagram for explaining the configuration and operation of the shading correction circuit of FIG. 1 in detail, and FIG. 8 is a flowchart for explaining the operation of the image reading apparatus of FIG. 1 in the SPU mode.

First, as shown in FIG. 2, this image reading apparatus has a contact glass 2 provided on an upper portion of a frame body 1.
A projecting unit (slide projector: slide projector: is configured to be able to read the upper reflection original (not shown) and the transparent original 14, and is roughly classified as shown on the right side of the figure.
SPU) II and a reading unit I for reading the reflective original and the transparent original 14 as shown on the left side of the drawing.

The reading unit I includes the frame 1 and the contact glass 2, the traveling body 3 which travels in the sub-scanning direction along the guide lot 8 by a driving source and a driving system (not shown) when reading a reflection original, and an analog. A printed circuit board 21 on which circuit components for processing signals are mounted and a printed circuit board 22 on which circuit components for processing digital signals are mounted are provided.

Light sources 7a and 7b for illuminating the reflection original on the contact glass 2, a converging optical transmission member 4, and a photoelectric conversion element 6 for converting the image of the reflection original into an electric signal are provided on the traveling member 3. CCD 38), and the color correction filter 5 for correcting the color sensitivity balance of the photoelectric conversion element 6 are provided.

Although not shown, the traveling body 3
Is also provided with a printed circuit board on which circuit components for driving the photoelectric conversion element 6 and for amplifying the output signal of the photoelectric conversion element 6 are mounted. 21 is connected.
Further, as is well known in the reading section I, the reflective original is scanned in the main scanning direction by the photoelectric conversion element 6, and the traveling body 3 is scanned.
Is moved to scan in the sub-scanning direction.

Next, the structure of the slide projector (SPU) II will be described with reference to FIGS. 2 to 4. First, the film 14 which is a transparent original is attached to the reference surface of the reference glass 15 by the pressing glass 13. It is pressed and moves in the sub-scanning direction. The light of the illumination optical system 10 having the lamp 9 and the like is corrected in light amount by the light amount correction means 11 shown in detail in FIG. 3, and is matched with the color of the reading optical system by the color correction filter 12 to illuminate the film 14.

As shown in FIG. 3, the light quantity correction means 11 includes eight ND filters 47-1 to 4-4 whose transmittances are different stepwise.
7-8 are arranged in the circumferential direction, and the ND filters 47-1 to
One of the motors 47-8 is rotated by the motor 46 so that it is placed in the optical path. In addition, the ND filters 47-1 to 47-8
Is not limited to eight, and the transmittance may be gradually different instead of stepwise.

As shown in FIG. 3, the transparent original image projected in this manner has its optical path folded back by the folding mirror 18 after being magnified by the projection magnifying lens 17, and the projection plate 19 placed on the contact glass 2. Projected on.
A diffusion surface is formed on the lower surface of the projection plate 19. At the time of this reading, the traveling body 3 is stopped at a predetermined position, and the film 14 is moved in the sub-scanning direction together with the pressing glass 13 and the reference glass 15 by the driving source 16 as shown in FIG. 6 is read line by line.

Next, the electrical construction will be described with reference to FIG. SPUII is an SPU control unit 30 having a CPU, etc.
And a mechanical drive unit 31 for driving each motor, a cooling fan and the like for film scanning, color correction filter switching and light amount correction, a lamp lighting circuit 32 for a light source, a home position detection of a film running body and a film cassette detection. The sensor unit 33 for use in the.

The reading section I includes a scanner control section 34 having a CPU and the like, a mechanical drive section 35 for driving a motor and a cooling fan for driving the traveling body 3, a lamp lighting circuit 36 for illuminating a reflected original, It is composed of a sensor unit 37 for detecting the home position of the traveling body and for detecting the temperature of the fluorescent lamp tube wall.

The circuit of the image signal system is processed by the CCD 38 as the photoelectric conversion element 6, an analog processing section 39 for amplifying the signal read by the CCD 38 and converting it into a digital signal, and the analog processing section 39. Shading correction circuit 40 for shading correction of a signal
Then, the signal processed by the shading correction circuit 40 is subjected to scaling, γ conversion, color conversion, etc., and in particular, when the 35 mm film is read, γ conversion and color conversion are performed so as to obtain output characteristics equivalent to those of a reflection original. It has a digital processing unit 41 for outputting to a printer or the like.

The shading correction circuit 40 is shown in FIG. 6 in order to correct the light amount unevenness in the main scanning direction of the light sources 7a and 7b of the reading section I and the lamp 9 of the SPUII, and the variation in the sensitivity of each pixel of the CCD 38. As shown, the read data of the outer frame base film area 14b of the film 14 is used as shading correction data, and the shading correction is performed when the actual image area 14a is read.

As shown in FIG. 5, the peak hold circuit 42 inputs in pixel clock units in order to hold the peak value of the read data of the outer frame base film area 14b of the film 14 in order to obtain this shading correction data. It comprises a digital comparator 43 for comparing the value of the image data to be processed with the peak value up to that time, and a latch 44 for storing the peak value.

The circuits 38 to 42 of the image signal system are operated by a timing signal being applied by the scanner controller 34, and by serial communication by optical fiber through the interface between the scanner controller 34 and the SPU controller 30. Commands, status and data are exchanged. The SPU control unit 30 controls the entire SPU II under the control of the scanner control unit 34.

Next, the operation of the above embodiment will be described with reference to FIGS. 7 and 8. First, in the setup process, S
When the PU mode is set, the SPUII is powered on by a command from the scanner control unit 34, the SPUII is initialized, and each load is set to the initial state (step S1).

Then, it is determined whether or not the negative mode is set, and the color filter for the negative is set (step S2),
Further, the SPU control unit 30 moves the traveling bodies 13 and 15 to the reading position, and the scanner control unit 34 sets the CCD 38 to SP.
Move to the projection position from UII. Then, the SPU controller 30 turns on the lamp 9 at the initial light amount value to turn on the film original 1
4 is pre-scanned (step S3), and after the light amount is corrected, scanning of the film original 14 is started (step S3).
4).

When the outer frame base film area 14b of the film original 14 reaches the reading position, the read data for a plurality of lines is taken in and averaged at each pixel of the CCD 38 to obtain the shading correction data shown in FIG. (Step S5).

Next, the image area 14 of the film original 14 is printed.
When a reaches the reading position, the shading correction data is read out and the shading correction calculation circuit 40a is read.
To the shading correction calculation circuit 4
0a corrects the image area 14a. Of course, the shading correction data is transferred so as to match the data read by the same pixel of the CCD 38.

Therefore, according to the above embodiment, the read data of the outer frame base film area 14b of the film original 14 is stored as the shading correction data, and the read data of the image area 14a is subjected to the shading correction. It is possible to read the orange base area of No. 1 and perform shading correction of the film original, and thus it is possible to obtain an image signal whose color balance is always stable.

Next, referring to FIG. 9 and FIG.
An example will be described. FIG. 9 is a block diagram showing a shading correction circuit of the second embodiment, and FIG. 10 is a flow chart for explaining the operation of the second embodiment.

In this embodiment, the data obtained by reading the reference negative orange base film is stored in the memory 40b as temporary shading correction data, and the film original 14 is stored.
The coefficient of the temporary shading correction data calculated from the read data of the outer frame base film area 14b of
It is detected by the B level ratio detection circuit 40c. The reference negative orange base film does not have to be the same type as the film original 14.

The operation will be described with reference to FIG. 10. First, when the SPU mode is set, the scanner control unit 34
SPUII is powered on by the command from
II is initialized and each load is set to the initial state (step S11).

Then, it is determined whether or not the negative mode is set, and the color filter for the negative is set (step S1).
2) Further, the SPU control unit 30 moves the traveling bodies 13 and 15 to the reading position, and the scanner control unit 34 sets the CCD 38.
To the projection position from SPUII. Then, when the orange base film is set (step S13)
The read data is fetched and stored as temporary shading correction data (step S14).

Next, when the film original 14 is set, the SPU controller 30 turns on the lamp 9 at the initial light amount value to prescan the film original 14 (step S1).
5) After the light amount is corrected, the scanning of the film original 14 is started (step S16). And the film original 1
When the outer frame base film area 14b of No. 4 reaches the reading position, the read data is taken in and the RGB level ratio detection circuit 34b causes the RG of the outer frame base film area 14b to be read.
The level ratio of B is detected (step S17).

When detecting the RGB level ratio, the RGB level of one pixel may be held to calculate the level ratio, or the RGB levels of all the pixels for one line may be averaged. The average value may be calculated from each average value, but the latter method can improve the accuracy although it is expensive for the averaging circuit.

Next, the image area 14 of the film original 14 is printed.
When a reaches the reading position, the temporary shading correction data in the memory 40b and the RGB level ratio detection circuit 4
The shading correction calculation circuit 40a performs correction by reading out the RGB level ratio detected by 0c and transferring it to the shading calculation correction circuit 40a.

That is, the data for correcting the temporary shading correction data when the reference negative orange base film is read are the sensitivity variation of each pixel of the CCD 38 and the light distribution in the main scanning direction of the optical system such as the light source.
RG according to the spectral distribution of the light source and the orange base film
Since it is determined by the B ratio, the RGB values of the orange base film and the outer frame base film area 14b of the original film 14 are determined.
By correcting the difference in the ratio, it is possible to obtain an image signal whose color balance is always stable.

Therefore, according to the above embodiment, the data obtained by reading the reference negative orange base film is stored as temporary shading correction data, and this data is corrected by the read data of the outer frame base film area 14b of the film original 14. Therefore, an image signal whose color balance is always stable can be obtained.

Next, a third embodiment will be described with reference to FIG. In this embodiment, a color filter for negative shading having the spectral characteristics of an orange base film is set and taken in as temporary shading correction data (steps S22 and S23), and the color filter for negative shading is removed and read for negative reading instead. The color filter of is set (step S24). And the second
Similar to the embodiment described above, the image area 14a is corrected by the data corrected by the read data of the outer frame base film area 14b of the film original 14 (steps S25 to S3).
0).

Therefore, also in this embodiment, similarly, the temporary shading correction data obtained from the negative shading color filter having the spectral characteristic of the orange base film is used as the read data of the outer frame base film area 14b of the original film 14. Since the correction is performed, it is possible to obtain an image signal whose color balance is always stable.

[0056]

As described above, according to the invention of claim 1, the projection means for projecting the negative film original, the image sensor for reading the original image projected by the projection means, and the image sensor for reading the image. A / D conversion means for converting the image signal into a multi-valued digital signal,
Shading correction means for generating shading correction data from the image signal of the outer frame base area of the negative film original read by the image sensor, and correcting the image signal of the image area of the negative film original with the shading correction data. Since it is possible to read the same orange-based image as the film original and perform shading correction on the film original, it is possible to obtain an image signal whose color balance is always stable.

According to a second aspect of the present invention, the shading correction means according to the first aspect averages image signals in pixels of a plurality of lines in the outer frame base region of the negative film original read by the image sensor. By doing so, shading correction data is generated, so accurate shading correction data can be generated,
Therefore, it is possible to obtain an image signal whose color balance is always stable.

According to a third aspect of the present invention, projection means for projecting a negative film original, an image sensor for reading the original image projected by the projection means, and a multi-valued digital signal for the image signal read by the image sensor. A / D conversion means for converting into a signal, and shading correction data is generated from the image signal of the reference negative orange base film read by the image sensor, and the level of the image signal of each color in the outer frame base region of the negative film original is generated. Since the coefficient of the shading correction data is detected from the ratio and the image signal in the image area of the negative film original is provided with the shading correction data and the shading correction means, the same orange as the film original is provided. Scan the base image to supplement the shading of the film original. It can be, therefore, it is possible to obtain an image signal color balance is always stable.

According to a fourth aspect of the present invention, a projection means for projecting a negative film original, a color correction filter for correcting the color sensitivity balance of the original image projected by the projection means,
An image sensor for reading an original image corrected by the color correction filter, and an A / D for converting an image signal read by the image sensor into a multivalued digital signal.
The conversion means and the spectral characteristics of the reference negative orange base film are transmitted through a shading correction filter arranged in place of the color correction filter, and shading correction data is obtained from the image signal read by the image sensor. The coefficient of the shading correction data is generated from the level ratio of the image signal of each color in the outer frame base area of the negative film original, and the image signal of the image area of the negative film original is detected and the coefficient of the shading correction data is detected. Since the shading correction means for correcting the film original is provided, the same orange-based image as the film original can be read to perform the shading correction on the film original, and thus an image signal with a stable color balance can be obtained.

The invention according to claim 5 is the invention according to claim 3 or 4.
Since the shading correction means described above calculates the coefficient of the shading correction data by averaging the image signals of the respective colors in the pixels of the plurality of lines of the outer frame base region of the negative film original read by the image sensor. Therefore, accurate shading correction data can be generated, and thus an image signal whose color balance is always stable can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an image reading apparatus according to the present invention.

FIG. 2 is a configuration diagram showing the image reading apparatus of FIG.

FIG. 3 is a perspective view showing the slide projector of FIG. 2 in detail.

FIG. 4 is a perspective view showing in detail the light amount correction means of FIGS. 2 and 3.

5 is a block diagram for explaining the configuration and operation of the peak hold circuit of FIG. 1 in detail.

FIG. 6 is an explanatory diagram showing a film original.

7 is a block diagram for explaining in detail the configuration and operation of the shading correction circuit of FIG.

8 is a flowchart for explaining the operation of the image reading apparatus in FIG. 1 in SPU mode.

FIG. 9 is a block diagram showing a shading correction circuit according to a second embodiment.

FIG. 10 is a flowchart for explaining the operation of the second embodiment.

FIG. 11 is a flowchart for explaining the operation of the third embodiment.

FIG. 12 is a flowchart for explaining the operation of the conventional example.

FIG. 13 is a flowchart for explaining the operation of the conventional example.

[Explanation of symbols]

 12 Color correction filter 14 Negative film original 14a Image area 14b Outer frame base film area 17 Projection magnifying lens 34 Scanner control unit 38 CCD 40 Shading correction circuit 40a Shading correction arithmetic circuit 40b Shading correction data memory 40c RGB ratio detection circuit 42 Peak hold circuit

Claims (5)

[Claims] 1. A projection means for projecting a negative film original, an image sensor for reading an original image projected by the projection means, and an A / A for converting an image signal read by the image sensor into a multi-valued digital signal. Shading correction data is generated from the D conversion means and the image signal of the outer frame base area of the negative film original read by the image sensor, and the image signal of the image area of the negative film original is corrected by the shading correction data. An image reading apparatus including: 2. The shading correction means generates shading correction data by averaging image signals in pixels of a plurality of lines of an outer frame base region of a negative film original read by the image sensor. The image reading apparatus according to claim 1, which is characterized in that. 3. A projection means for projecting a negative film original, an image sensor for reading the original image projected by the projection means, and an A / which converts the image signal read by the image sensor into a multi-valued digital signal. Shading correction data is generated from the image signal of the reference negative orange base film read by the D conversion means and the image sensor, and the shading correction is performed from the level ratio of the image signals of the respective colors in the outer frame base region of the negative film original. An image reading apparatus comprising: a shading correction unit that detects a coefficient of data and corrects an image signal of an image area of a negative film original with the shading correction data and the coefficient. 4. A projection unit for projecting a negative film original, a color correction filter for correcting the color sensitivity balance of the original image projected by the projection unit, and an image sensor for reading the original image corrected by the color correction filter. An A / D conversion means for converting an image signal read by the image sensor into a multi-valued digital signal; and a shading having the spectral characteristics of a reference negative orange base film and arranged in place of the color correction filter. Shading correction data is generated from the image signal read by the image sensor after passing through the correction filter, and the coefficient of the shading correction data is calculated from the level ratio of the image signal of each color in the outer frame base region of the negative film original. Is detected, and the image signal of the image area of the negative film original is detected by the shader. Image reading apparatus and a shading correction means for correcting by the coefficient ring correction data. 5. The shading correction means averages image signals of respective colors in pixels of a plurality of lines of an outer frame base region of a negative film original read by the image sensor to obtain coefficients of shading correction data. It calculates, Comprising: 3 or 4 characterized by the above-mentioned.
The image reading device described.