JPH0369230B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multicolor document reading device, and particularly to a ghost correction mechanism.

[Prior art]

A method that has recently attracted attention as a method for reading multicolor images on the document surface is called the raster scan light source switching method, which synchronizes multiple light sources with different spectral characteristics with the document reading scan cycle of the image sensor. and scan each one while blinking them sequentially, and sequentially image the reflected light from the document on an image sensor, thereby obtaining a number of photoelectric conversion signals corresponding to the number of light sources for the same scanning line of the document, Thereafter, the color of the image in the scanning line of the document is determined based on the levels of these photoelectric conversion signals.

By the way, when reading a multicolor image as described above, colors that are not present in the actual document may be read at the boundaries between colors. This is called color ghosting and is a serious problem in reading multicolor images.

This is because when reading a multicolor image, multiple color signals are obtained from the same pixel and the combined output is output as the read signal, but due to misalignment of these reading positions or chromatic aberration of the lens, etc. Due to the deviation in the reading process,
It is thought that a shift occurs in the color signal, resulting in a color ghost.

For example, as shown in FIG.
A thin line c made of the third color may appear at the boundary between the color area b and the second color area b. Conventionally, such a thin line is determined to be a ghost, and the thin line is erased as shown in FIG. 2. However, with this method, even if the line was originally a thin line, it would be erased, so it was not an accurate correction method.

In other words, conventional multicolor document reading devices use a mechanism that erases all thin line parts without determining whether they are color ghosts or original thin lines, resulting in extremely inaccurate correction. It was a mechanism.

[Purpose of the invention]

The present invention was made in view of the above circumstances, and
It is an object of the present invention to provide a color document reading device equipped with a color ghost correction mechanism capable of correcting even fine line portions.

[Structure of the invention]

In order to achieve the above object, the present invention provides a multicolor document having a first image sensor that reads a first color and a second image sensor that reads a second color that has a lower reflectance than the first color. In the reading device, a comparison means for comparing the level of a first read signal read by the first image sensor of a pixel of interest and a pixel adjacent thereto with a preset threshold value, and a pixel adjacent to the pixel of interest If there is a pixel whose reading level is lower than the threshold value, the read signal of the first color of the pixel of interest is a ghost for the second color of the pixel of interest read by the second image sensor. The present invention is equipped with a ghost recognition means for determining the following, and a color separation means for selecting a sensor read signal and a color separation signal based on the output of the ghost recognition means.

For example, we focused on the fact that a color ghost that occurs as red in a thin line area that should originally be black and a detail that is originally red are different in the surrounding red signal level even though the color of the pixel is the same. The level of the read signal for the color of interest of the pixels in the vicinity of the pixel of interest is compared with a predetermined threshold value, and the level of the read signal of the color is determined for the neighboring pixels. If there is a signal lower than the threshold value, the read signal of the pixel of interest is determined to be a ghost, and the color ghost correction mechanism is configured to correct the ghost.

That is, as shown in FIGS. 3 and 4,
Even though the signal at position P is the same red, there are cases where it is a real image and cases where it is a ghost. FIG. 3 shows the case of a real red thin line, which has a red level R1, which is true red, and a black level B1. Further, FIG. 4 shows a red ghost that appears near the black thin line, and has a red level R1 and a black level B2, which are ghosts. in this way,
There is a difference in signal level between the actual red and the ghost red, and it can be seen from FIG. 4 R2 that the signal level is lower in the vicinity of the target position P for the ghost red. Therefore, by setting a threshold value L for ghost detection between the red level of the real image and the red level of the ghost, it is possible to determine whether or not it is a ghost by comparing the threshold value with the output value of the color signal. It is an attempt to determine whether

〔Example〕

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

The following is an example in which the present invention is applied to a two-color original reading device for reading two colors, red and black.

As shown in FIG. 6, this device includes first and second image sensors 1 and 2 for reading a red image and a black image, respectively, and output signals from the first and second image sensors 1 and 2 to read an original. It is comprised of a color discrimination circuit 3 for discriminating the color of the color. Furthermore, this color discrimination circuit 3 includes a color discrimination circuit 4 for determining the color of the document from the output signal R of the first image sensor 1 and the output signal B of the second image sensor 2, and The ghost recognition circuit 5 is configured to determine whether or not it is a ghost, and to emit a ghost signal if it is a ghost, performs ghost correction and performs color separation using the output signals R and B and the ghost signal. It has a color separation circuit 6 for carrying out this process.

As shown in FIG. 5, the ghost recognition circuit 5 detects the first image sensor 1 for eight adjacent pixels C _{1 .} . . C ₈ vertically, horizontally, and diagonally adjacent to the pixel C 0 of interest.
It is detected whether or not there is an output signal R, that is, a red reading signal R, which is smaller than a predetermined reference level S, and if it exists, the red reading signal R of the target pixel _C0 is a ghost. It is configured to determine that this is the case and to issue a ghost signal G. As shown in FIG. 7, the configuration includes a reference level setting system 11 and a determination as to whether the red reading signal R is higher than the reference level S set by the reference level setting system 11 (1) or not (0). Compare the
A comparator 12 for outputting as a 1,0 signal and _a first latch system 1 for latching the outputs of the comparator 12 for the pixel of interest C0 and the adjacent pixels _C1 ... _C8 .
3, and if at least one of the nine outputs from the latch system is 0, it is determined that it is a ghost, and the output is set to 1 (a ghost signal),
If all of the nine outputs are 1, then
Configured to be 0 (not a ghost)
It consists of ROM14.

Here, the first latch system 13 is connected to the comparator 1
The first and second line memories 15 and 16 are connected in series to the output of No. 2, and the first and second line memories are connected in parallel to the output of No. 3. two latch circuits L ₅ ,
L ₁ , L ₆ and three latch circuits L ₃ connected in series to the output of the first line memory 15,
L ₀ , L ₄ and three latch circuits L ₇ , which are connected in series to the output of the second line memory 16.
The outputs of these latch circuits L ₀ ... _{L 7 correspond} to the pixels C ₀ ...C _{8 ,} respectively.

Note that the reference value level setting system 11 is set at 50% when the maximum level of the red read signal is 100%.
This level is determined as a threshold value, and this is set as a reference value S.

Further, the output of the first image sensor 1, that is, the red reading signal, is input to the color separation circuit via the third line memory 17 and the second latch circuit 18 in order to synchronize the timing with the output of the ghost recognition circuit. There is.

Furthermore, the output B of the second image sensor is also sent to the fourth line memory 19 and the third line memory 19 in order to synchronize the timing with the output of the ghost recognition circuit.
The signal is inputted to the color separation circuit via the latch circuit 20 of FIG.

The color separation circuit is configured to determine which of the red reading signal and the black reading signal to output based on this input information, and to output the signal.

Next, the operation of this two-color original reading device will be explained.

First, the red reading signal R and the black reading signal B read by the first image sensor 1 and the second image sensor 2, respectively, are input to the color judgment circuit 4, and are converted into color signals and sent to the color separation circuit. is output to.

Further, the red reading signal R is input to a ghost recognition circuit, and first, by a comparator 12,
It is determined whether or not it is greater than a reference value S. At this time, it is assumed that 1 is output when the value is large, and 0 is output when it is not large. This output is the latch system 13
, and the output of each latch circuit is
The data is input to the ROM 14, and it is determined whether or not 0 exists among these. If 0 exists, it is determined that it is a ghost, and a signal indicating that the red signal of this pixel of interest C ₀ is a ghost, that is, a level 0 is output. If all the outputs of the latch circuit are 1, that is, if there is no 0, it is determined that there is no ghost, and the ROM 14 outputs an output indicating that the red signal of the target pixel _C0 is not a ghost, that is, level 1.

In this way, it is determined whether the output of the red reading signal corresponding to the pixel of interest _C0 is a ghost, and if it is a ghost, the output of the black reading signal is output from the color separation circuit. Further, if it is not a ghost, a red reading signal is output from the color separation circuit.

Therefore, correction is performed even on thin lines that appear at the boundaries between colors, after determining whether or not they are color ghosts, so that two-color originals can be read correctly.

Note that the threshold level used as the reference value S may be set as appropriate depending on the color.

〔Effect of the invention〕

As described above, according to the multicolor original reading device of the present invention, the level of the read signal for the color of interest of the pixel in the vicinity of the pixel of interest is compared with a predetermined threshold value, Color ghost correction configured to determine that the read signal of the color of the pixel of interest is a ghost if there is a nearby pixel in which the level of the read signal of the color is lower than the threshold value. Since this mechanism is provided, it is possible to correct color ghosts after correctly determining whether or not thin line portions are color ghosts, thereby making it possible to read images correctly.

[Brief explanation of drawings]

Figure 1 shows an example of the occurrence of a thin line, Figure 2 shows the situation when the thin line is erased, Figure 3 shows an example of a signal when it is not a ghost, and Figure 4 shows a case where it is a ghost. FIG. 5 is a diagram showing a two-color document reading device according to an embodiment of the present invention, and FIG. 6 is a diagram showing an example of a signal.
The figure shows the pixel of interest _C0 and its eight adjacent pixels _C1 ... _C8 , and FIG. 7 is a block diagram showing the ghost recognition circuit in the apparatus shown in FIG. DESCRIPTION OF SYMBOLS 1...First image sensor, 2...Second image sensor, 3...Color discrimination circuit, 4...Color judgment circuit, 5...Ghost recognition circuit, 6...Color separation circuit, 11...Reference Level setting system, 12... Comparator, 13... First latch system, 14...
ROM, 15...first line memory, 16...
Second line memory, 17...Third line memory, 18...Second latch circuit, 19...Fourth line memory, 20...Third latch circuit, R...
...Red reading signal, B...Black reading signal,
L ₀ ...L ₈ ...Latch circuit.

Claims (1)

[Claims] 1. A multicolor document reading device including: a first image sensor that reads a first color; and a second image sensor that reads a second color that has a lower reflectance than the first color. Comparing means for comparing the level of the first color read signal read by the first image sensor of the pixel of interest and the pixel adjacent thereto with a preset threshold value, and the pixel of interest and the pixel adjacent thereto; If there is a pixel whose reading level is lower than the threshold value, the read signal of the first color of the pixel of interest is a ghost for the second color of the pixel of interest read by the second image sensor. and a first ghost recognition means based on the output of the ghost recognition means.
Alternatively, a multicolor document reading device comprising: color separation means for selecting a read signal from the second image sensor.