JPS63208366A - Shading correction method - Google Patents

Abstract

PURPOSE:To attain correct shading correction even with flaw or dirt on a white level calibration plate by providing a circuit comparing a picture data read by plural lines in the subscanning direction with the shading correction data and a secting circuit. CONSTITUTION:A comparing circuit 12 compares a picture data A at the read by plural lines with a shading correction data B read by a shading RAM 11 to decide a white reference level of an image pickup element. Moreover, a selection circuit 13, based on a write control signal, selects either of data A, B which is larger and outputs it as a data C in the RAM 11. Then the next address of the RAM 11 is read and the similar operation as to each bit in the main scanning direction and when all of one lie is finished, the reading of 2-line and 3-line is consecutive. Then a wide sufficiently wide as to a small flaw or dirt on the white level calibration plate is applied and the shading correction is applied accurately even with flaw or dirt on the white calibration plate.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a shading correction method suitable for use in, for example, reading devices, facsimile reading sections, and the like.

BACKGROUND OF THE INVENTION A conventional shading correction method has been implemented by an apparatus shown in FIG. FIG. 5 is a timing chart for the correction.

In other words, in FIGS. 4 and 5, the image data A when the white calibration plate is read is stored in the shading data RAM 1 at one point in the main scanning direction based on the write control signal.
Lines are written.

Next, when reading the actual document, the shading data RAM is stored based on the image data A and the readout control signal.
The shading correction circuit 2 performs shading correction using the shading correction data B read from the shading correction data B read from the shading correction data B read from the shading correction data B read from the shading correction data B read from the shading correction circuit 2, and obtains corrected output data C.

Problems to be Solved by the Invention However, with this configuration, it is easy to be affected by non-uniformity of the white calibration plate due to scratches, dirt, dust, etc. on the white calibration plate for creating shading correction data. Unable to obtain accurate shading correction data1.
Therefore, flaws such as lines and stripes may occur in the reproduced image after shading correction.

In other words, the white calibration plate may change over time due to dirt, dust, etc., or may become scratched due to human causes, so the white reference level may partially change. be.

Therefore, it is not preferable to determine the white reference level by reading one line in the main scanning direction as in the past because it is impossible to avoid the effects of dirt, scratches, etc.

As a solution to this problem, there is a method of taking the average of a plurality of pixels in the main scanning direction or the sub-scanning direction, for example. However, these methods have the following problems.

That is, the method of taking the average of a plurality of pixels in the main scanning direction makes it impossible to correct bit variations in adjacent image sensors.

Furthermore, the method of taking the average of a plurality of pixels in the sub-scanning direction requires a line memory for a plurality of pixels, resulting in an enormous amount of circuitry (number of parts, etc.).

The present invention has been made in view of the above-mentioned problems, and provides a shading correction method that can perform accurate shading correction even if the white calibration plate has scratches, dirt, etc. by adding a simple circuit. The purpose is to provide.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention performs shading correction on the largest value larger than white among the image data read from the white calibration plate for multiple pixels in the sub-scanning direction. The shading data is stored in the shading data RAM as data for use, and when the original is read, the shading data RA
The configuration is such that shading correction is performed using M data and image data.

Effect of the Invention With the above-described configuration, the present invention shades data of a level that is the highest than white and data of a level that is closer to white among a plurality of pixels in the sub-scanning direction when a white calibration plate is read. Since the data can be used as correction data, the influence of scratches, dust, etc. on the white calibration plate can be removed, and accurate shading correction can be performed.

Embodiment FIG. 1 is a block diagram showing a schematic configuration of an apparatus suitable for implementing the shading correction method according to the present invention.

In FIG. 1, there is a shading correction circuit 10 for performing shading correction, and a shading data RAM 1 for storing shading correction data.
1 is the same as the conventional example shown in FIG. 4, but a comparison circuit 12 and a selection circuit 13 are newly added.

The comparison circuit 12 reads image data A and shading data RAM II obtained by reading a plurality of lines of a white calibration plate in the sub-scanning direction in advance in order to determine the white reference level of the image sensor. This circuit compares the shading correction data B read from the shading correction data B.

Further, the selection circuit 13 selects the larger one of the image data A and data B based on the write control signal, and sets this as data C to the shading data RA.
This is a circuit that outputs to MII.

Note that D is a write/read control signal, and E is output data after aging correction.

Figure 2 shows the shading 6-- in the apparatus of Figure 1.
2. This is a timing chart during correction. FIG. 3 is a flowchart for explaining the operation when reading the white calibration plate in the apparatus shown in FIG. 1. In FIG. 3, ST1
~ST9 shows each step of the flowchart.

To explain the operation below, first, a white calibration plate is read. At that time, according to the flowchart in Fig. 3, the shading data RAM 11 is cleared in ST1, and the ST
2, the shading data RAM 11 is read and data B is obtained.

Next, the comparison circuit 12 compares the data B and the image data A from the shading data RAMII (5T3), and the selection circuit 13 selects the data C with a level closer to white, and the data C is used as the shading data RAMII. Write to the same address (ST4
．． ST5, 5T6).

Next, in ST7, the shading data RAM
Read the next address of II.

The above operations are performed sequentially for each bit in the main scanning direction, and when all lines are completed (ST8), similarly,
Execute reading of 2nd line and 3rd line, line < (Sr
1).

Then, when a sufficiently wide range of reading is performed for small scratches, dust, etc. on the white calibration plate, the reading operation of the white calibration plate based on the flowchart of FIG. 3 is completed.

Thereafter, when the document is actually read, the shading correction circuit 1o performs shading correction using the image data A and the data B (data at a level closer to white) read out from the shading data RAMII.

In addition, in this embodiment, compared to the conventional example (see Fig. 4),
Only the comparison circuit 12 and selection circuit 13 are added,
The circuit configuration does not become complicated or bulky.

Effects of the Invention As is clear from the above-described embodiments, the present invention uses, for multiple pixels in the sub-scanning direction, the value that is largest than white out of the image data read from the white calibration plate as data for shading correction. , is stored in the shading data RAM, and when reading the original, shading correction is performed using the shading correction data in the shading data RAM and the image data, so it is a relatively simple addition to the conventional apparatus. By adding this circuit, accurate shading correction can be performed without being affected by fluctuations in the white reference level due to scratches, dirt, dust, etc. on the white calibration plate.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of a device suitable for implementing the shading correction method according to the present invention, FIG. 2 is a timing chart of the device in FIG. 1, and FIG. 3 is a white color diagram of the device in FIG. FIG. 4 is a block diagram showing a schematic configuration of an apparatus for carrying out a conventional shading correction method, and FIG. 5 is a timing chart of the apparatus shown in FIG. 4. 10... Shading correction circuit, 11... Shading data RAM, 12... Comparison circuit, 13...
・Selection circuit.

Claims (1)

[Claims] Among the image data obtained by reading a white calibration plate for pixels of multiple lines in the sub-scanning direction to determine the white reference level of the image sensor, the data with the highest level than white is used as shading correction data. A shading correction method characterized in that the method is used during shading correction calculation processing.