JPH04235466A - Image reader - Google Patents

Abstract

PURPOSE:To enable a shading correction while reducing an error by reading a white reference original at plural positions plural times. CONSTITUTION:The image reader reads white reference original, stores it as the reference data and reads the image of an original while performing the shading correction correcting the original image data based on the reference data. In the reader, the white reference original or black reference original is read at plural positions, the reading is executed plural times at the respective positions and stored in a white reference memory 14 or a black reference memory 15, they are added in an adder circuit 12, an average of them is taken in a correction circuit 16 and used as the reference data.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device for reading image data, such as a facsimile machine or an image scanner.

0002

2. Description of the Related Art Image signals obtained by electronic scanning include an error called shading. This occurs because it is difficult to apply uniform light to the entire reading line on the document, and because it is difficult to manufacture each light receiving element in the image sensor to have the same sensitivity. Shading correction is a preprocessing process that corrects such errors so that images can always be read correctly.

First, a conventional image reading device and a shading correction method will be explained using FIGS. 6 and 7. Figure 6
, 51 is a CCD one-dimensional image sensor, 52
53 is a lens, 53 is a lamp that illuminates the document, and 54 is a carriage that holds these. Reference numeral 55 denotes a transparent plate on which an original or the like is placed, and 56 is an original placed on the transparent plate. Reference numeral 57 denotes a white reference document placed on the transparent plate 55.

In FIG. 7, reference numeral 58 is an analog-to-digital converter (hereinafter referred to as A/D converter) that converts image data of an analog signal input from an image sensor into a digital signal.
It is abbreviated as a converter. ), 59 is a line averaging processing means for reducing mixed random noise by averaging one line of data, and the CPU actually performs the processing. 60 is a read/write memory (hereinafter referred to as RAM) that stores the averaged data, and 61 is a read-only memory (hereinafter referred to as ROM) that stores normalized data.

The operation will be explained below. First, before reading the image on the original 56, the carriage 54 is stopped under the reference original 57, and the white image on the reference original 57 is read. At this time, the switch 62 is turned to the a side, and the read data is averaged and stored in the RAM 60 as reference data. Next, the image on the document 56 is read while moving the image sensor 51 in the direction of arrow c. At this time, the switch 62 is tilted to the b side, and the reference data is read out from the RAM 60 at the same time as the image on the document 56 is read. The data read from the original 56 and the reference data already created and stored in the RAM 60 are sent as address data to the ROM 61, and the ROM 61 outputs normalized data stored at each address.

[0006]

[Problems to be Solved by the Invention] However, when the white reference original 57 is read only once and used as reference data as has been done in the past, errors in the electrical system, dirt, scratches, or dust on the white reference original may occur. There was a problem in that the concentration error directly became a reference data error.

[0007]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention includes means for reading a reference document multiple times at the same location, and means for changing the location of the document read by the reading means. and calculation means for averaging the plurality of reference data read by the reading means, and the output of the calculation means is used as a reference for shading correction.

[0008]

[Operation] As a result, the reference original is read multiple times at multiple locations, stored in memory, and averaged to create reference data.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a control unit that controls the device;
3 is a reading unit that optically reads the image of the original; 3 is a document transport unit that transports the original so that the reading unit 2 can read the original; 4 is a unit that transfers the image data sent from the reading unit 3
5 is a shading correction circuit that performs shading correction on the A/D converted image data; 6 is an enlargement/reduction circuit that enlarges or reduces the shading-corrected image data; 7 is an enlargement or reduction circuit; A halftone dot forming circuit performs halftone dot processing on the reduced image data, and 8 is a line buffer into which the halftone image data is temporarily written.

In FIG. 2, 11 is a control circuit that controls this circuit, 12 is an addition circuit that adds to the read white or black reference data, and 13 is the addition of the white or black reference data by the addition circuit 12. 14 is a 16-bit white reference memory used for addition of white reference data by the adder circuit 12; 15 is a 16-bit shared memory used for
16 is a 16-bit black reference memory used for addition of black reference data by the adder circuit 12, and 16 is a white and black reference data stored in the white reference memory 14 and the black reference memory 15. This is a correction circuit that corrects the image data.

The operation of the image reading apparatus of this embodiment configured as described above will be explained below with reference to the flowchart of FIG. First, in S31 and S32, the reading unit 2 reads the white reference original 21 and the black reference original 22 (not shown) provided in the original transport unit 3, and
After converting the data into a digital signal via the /D converter 4, the data is stored in the shared memory 13 in the shading correction circuit 5 as reference data. Next, in S33, after the original is transferred by the original transport unit 3, the reading unit 2 optically reads the image of the original, and the A/D converter 4 performs A/D conversion.
The signal is sent to the shading correction circuit 5. In S34, the shading correction circuit 5 performs shading correction on the image data based on the previously stored white and black reference data. The corrected image data is subjected to enlargement/reduction processing and halftone processing in S35 and S36, and then temporarily stored in the line buffer 8 in S37 and output to an external device.

Next, the operation of reading the white reference and black reference data will be explained using the flowchart of FIG. 4 and FIGS. 1 and 2. In S41, a counter 1 (not shown) in the control unit 1 is initialized to 0, and the process is started. When the counter 1 is incremented by 1 in S42, the white reference original 21 is transported by the original transport unit 3 to the position where the data of the reading unit 2 is read in S43. Next, in S44, the control unit 1
Counter 2 within is initialized to 0, and 1 is added to counter 2 in S45. In S46, the white reference data is read by the reading section 2. The read white reference data is sent to the shading correction circuit 5 via the A/D converter 4. The white reference data sent to the shading correction circuit 5 is written into the shared memory 13 via the addition circuit 12 by the control circuit 11 in S47. This S
S4 until steps 45 to S47 are repeated 16 times in total.
Feedback can be given at 8. That is, the white reference data at the same location is read 16 times, and the value added by the adding circuit 12 is written into the shared memory 13.

After reading the white reference data at the same location 16 times in this way, the process is fed back to S42 via S49, and in S43, the document transport unit 3 detects a location different from the previous reading location due to the action of the control unit 1. Move to a location. The steps S45 to S48 are repeated until the white reference data is read 16 times at this location.

[0014] In S49, it is determined whether the white reference data has been read 16 times at different locations, and if it is less than 16 times, the process returns to S42 again as described above, and the steps S42 to S49 are repeated.

[0015] As described above, 1
By reading the white reference data six times each, a total of 256 pieces of data are finally stored in the white reference memory 14. The shared memory 13 and the white reference memory 14 store reference data in 16 bits, and finally, by using the upper 8 bits of the white reference memory 14, 256 bits are stored.
The average data can be used as white reference data for shading correction.

Note that the capture of the black reference data is the same as the capture of the white reference data except that the black reference memory 15 is used instead of the white reference memory 14, so a description thereof will be omitted.

Finally, the process of correcting image data based on white reference data and black reference data will be explained using the flowchart of FIG. 5 and FIGS. 1 and 2. In S51, as the document transport section 3 moves, the reading section 2 reads the image on the document. The read image data is A/D converted by an A/D converter 4 and sent to a shading correction circuit 5. In S52, the shading correction circuit 5 reads the upper 8 bits of the white reference data and black reference data stored in the white reference memory 14 and the black reference memory 15,
3, the image data is corrected, and in S54,
The corrected image data is output in S53.

As described above, according to this embodiment, (1) it can be realized with relatively simple hardware; (2) The electrical system S/N ratio does not accumulate in the read S/N ratio as reference data. (3) The S/N ratio due to non-uniformity of the reference original does not accumulate in the S/N ratio of reading. (4) Although it is generally difficult to use an image reading device in an environment with a lot of dirt and dust, deterioration in reading quality can be significantly improved even if dirt adheres to the reference document. Therefore, an image reading device with high reading quality can be realized with a relatively simple hardware configuration.

[0019]

[Effects of the Invention] The present invention reads reference data multiple times at a plurality of different locations and performs shading correction using the data obtained by averaging the data as a reference. It is not directly accumulated in subsequent data. Further, the S/N ratio due to non-uniformity of the reference document is not directly accumulated in the data after shading as the reference data. Further, even if dust or the like adheres to the surface of the reference document, the reading quality does not deteriorate significantly, so that high reading quality can be maintained even if the usage environment conditions change.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an image reading device in an embodiment of the present invention.

[Fig. 2] Circuit block diagram of shading correction circuit 5

[
FIG. 3: Flowchart of the shading correction method according to this embodiment

[Figure 4] Flowchart of operation for reading reference data

[
Figure 5: Flowchart of the process of correcting image data based on reference data

[Figure 6] Cross-sectional view of a conventional image reading device

[Figure 7] Circuit block diagram of shading correction method

[Explanation of symbols]

1 Control section 2 Reading section 3. Original transport section 4 A/D converter 5 Shading correction circuit 6 Enlargement/reduction circuit 7 Halftone circuit 8 Line buffer 11 Control circuit 12 Adder circuit 13 Shared memory 14 White reference memory 15 Black reference memory 16 Correction circuit

Claims (1)

[Claims] 1. An image reading device that reads a white reference original, stores it as reference data, and reads an image of the original while performing shading correction that corrects the image data of the original based on the data, wherein the white reference comprising means for reading a document multiple times at the same location, means for reading the white reference document at a plurality of locations, and arithmetic means for averaging a plurality of reference data obtained by combining these means, the arithmetic means An image reading device characterized in that the output of is used as a reference for shading correction.