JPS62183681A - Quantization system for picture signal - Google Patents

Abstract

PURPOSE:To correctly quantize a picture signal by sampling the average level of the picture signal based on an output of an image sensor corresponding to respective black and white reference plates and making the average levels to the respective black and white reference plates a black reference value and a white reference value. CONSTITUTION:Before an original 1 is read by the image sensor 2, the prescribed area E1 of the white reference plate 3 is read and the prescribed are E2 of the black reference plate 4. Then, the average level of the picture signal based on the output of the image sensor 2 corresponding to the respective reference plates 3, 4 is sampled. The average level to the sampled white reference plate 3 is decided as the white reference value and the average level to the black reference plate 4 is decided as the black reference value. Thereafter, the original 1 is read by the image sensor 2 and the picture signal based on the output of the image sensor 2 during the reading is quantized according to the black reference value and the white reference value decided as mentioned above. Accordingly, the respective black and white reference values are not varied according to the fluctuation in the output of the image sensor 2.

Description

[Detailed Description of the Invention] [About TI! ] Quantization of an image signal in which the image signal is quantized based on a predetermined white reference value and black reference value in order to convert the image signal based on the image sensor output at the time of reading the original fa into multi-tone data. In order to enable more accurate quantization of image signals, the above quantization method is used. ! The reliability of the white reference value and black reference value, which serve as the foundation, can be made higher.

[Industrial Application Field] The present invention converts an analog image signal from an image sensor when reading a document such as a photograph into multi-gradation image signal data by converting the image signal into predetermined white reference values and black reference values. The present invention relates to a method for quantizing an image signal in which quantization is performed based on the following.

[Prior Art] In recent years, originals such as photographs are read with an image sensor such as a COD, an image signal based on the image sensor output is converted into multi-gradation data (m-light information), and the obtained multi-level data is Printed matter corresponding to the above-mentioned photograph, etc. is produced by performing halftone processing based on the tone data.

Here, in order to convert the above image signal into multi-gradation data,
Generally, the image signal is suspended (Δ/D change 1@) based on a predetermined white reference value and black reference value. The white reference value and black reference value used for such image signal suspension are determined by taking into account fluctuations in the light source for reading the original, uneven light irradiation, and variations in the photoelectric conversion performance of image sensors such as COD. Before actually reading a document, a white reference target and a black reference target are read by the image sensor, and the image sensor output is determined based on the image sensor output at that time.

Conventionally, the white reference value and black reference value have been determined as follows, for example.

A white reference plate and a black reference plate prepared in advance are irradiated with a reading light source, and the reflected light at a predetermined position on the reference plate is detected by an image sensor, for example, COD, for one line. The white reference ((α) or black reference value was determined based on the CCD output. In particular, regarding the black reference value, the CC
He even made decisions based on the D output.

[Problems to be Solved by the Invention] By the way, in the conventional image signal hanging method in which the white reference value and the black reference value are determined as described above, accurate quantization may not be possible. .

This is because an image sensor detects the reflected light at a predetermined position on each reference plate, and each reference value is determined based on the image sensor output. In some cases, there is a possibility that the white reference value is decided based on the image sensor output at that position, and if we look at the black reference value, there is a possibility similar to the case where white 8 is the quasi-value. , especially when looking at the image sensor output when the reading light source is turned off.
This is because it is affected by other light coming around.

That is, in the conventional image signal suspension method, the reliability of the white reference value and the black reference value was not necessarily high.

Therefore, an object of the present invention is to improve the reliability of the white reference value and the black reference value.

[Means for Solving the Problems] As shown in FIG. 1, the present invention, as shown in FIG. It is assumed that the image signal quantization method is quantized (C) based on B) and
In the image signal quantization method, the technical means for solving the above problem is as shown in FIG. The average level of the image signal is read by the image sensor 4t2 and is based on the output of the image sensor 2 corresponding to each of the reference plates 3.4 mentioned above is extracted (D1) (D2). is the white reference value (8), and the average level for the black reference plate 4 is the black reference value (B).

[Operation] Before the image sensor 2 reads the document 1, the image sensor 2 reads a predetermined area E1 of the white reference plate 3 and also reads a predetermined area E2 of the black reference plate 4. Then, the average level of the image signal based on the output of the image sensor 2 corresponding to each reference plate 3, 4 is extracted, and the extracted average level for the white reference plate 3 is determined as the white reference value, and the black reference value is determined. The average level for board 4 is determined as the black reference value. Thereafter, the original 1 is read by the image sensor 2, and an image signal based on the output of the image sensor 2 at the time of reading is quantized based on the white reference value and black reference value determined as described above.

When determining the above white reference value and black reference value, if there are scratches or the like within the predetermined area E1 of the white reference plate 3 or within the predetermined area E2 of the black reference plate 4, the output of the image sensor 2 at that position may be Even if there is a large fluctuation, the average level of the image signal based on the output of the image sensor 2 is used as the reference value for each black and white, so each black and white standard value will fluctuate significantly due to fluctuations in the output of the image sensor 2. Never.

[Embodiments of the invention] Embodiments of the present invention will be described below based on the drawings.

FIG. 2 is a diagram showing an example of a mechanical system related to image reading in a system that implements the image signal conversion method according to the present invention.

In the figure, a document 11 on which characters, figures, etc. are drawn is set at a predetermined position on a document table 12 made of a transparent material such as glass, with the side on which the characters, etc. are drawn facing down. In front of the reading start position of the original 11 (on the left in the drawing), a black reference board 13 and a white reference board 14 are arranged side by side in the reading direction.

Further, a carriage 20 that moves in the horizontal direction is arranged below the document table 12 and each of the reference plates 13 and 14, and the following items are accommodated in this carriage 20. It consists of a light source 21 for illuminating the original and a reflecting mirror 22.
, 23° 24 and a lens 25, a C0D 26 as an image sensor, and an amplifier 27 that amplifies the output signal from the C0D 26.

When the carriage 20 moves, the light reflected from each reference plate 13.14 or the document 11 irradiated by the light source 21 is reflected by the reflection mirrors 22, 23, 24 and the lens 2.
5 to the C0D 26, and the output of the C0D 26, which changes as the carriage 20 moves, is supplied to the next stage as a video signal via an amplifier 27.

On the other hand, the basic diagram of the circuit related to image signal quantization is the third one.
It is as shown in the figure.

In the same figure, reference numeral 30 denotes a white reference creation circuit, and in the above-mentioned mechanical system, this white reference creation circuit 30 is used to generate an amplifier 2 when the carriage 20 is moving below the white reference plate 14.
A white reference value is created based on a video signal (image signal) outputted via 7. 40 is a black reference generation circuit, and this black reference generation circuit 40 is connected to the carriage 20.
A black reference value is created based on the video signal outputted via the amplifier 27 while the veneer is silently moving below the veneer 13. 50 is an A/D conversion circuit that digitally converts the video signal V, and this A/D conversion circuit 50
, the white reference generation circuit 30h1 is used as the upper limit reference value.
The white reference value (voltage level) RT from these is input, and the black reference 1fl (voltage level) RB from the black reference generation circuit 40 is input as the lower limit reference value. The A/D conversion circuit 50 is configured to proportionally convert the video signal (2) into digital data based on the white reference value RT as the upper limit and the black reference value RB as the lower limit.

That is, the output of the A/D conversion circuit 50 becomes the quantized output of the video signal.

Here, the white reference generation circuit 30 and the black reference generation circuit 40
The specific structure is similar, for example, as shown in FIG.

This has a configuration in which comparators 31, 32, ROM 33, shift register 34, D/A converter 35, and voltage divider 36 are connected in series. And comparator 31
inputs the video signal and the output signal of the D/A converter 35, and the comparator 32 receives the output signal from the voltage divider 36 that divides the video signal and the output signal level of the D/A converter 35 at a predetermined ratio. When the video signal level is higher than the other input signal level, the output of each comparator 31 and 32 is 1 level (1 level).
The OM 33 uses the outputs of the comparators 31 and 32 (1 bit each) and the output of the shift register 34 (e.g. 8 bits) as address bit inputs, and the relationship between this address information and storage information, that is, the input of the ROM 33, is The logic between outputs is as shown in the attached table.

The ROM 33 is accessed based on a control signal from a control circuit (not shown), and the read data is stored in the shift register 34 at a predetermined timing. Then, the data stored in this shift register 34 is D/A converted by a D/A converter 35. In the case of the black reference generation circuit 40, this D/A converter 35 converts the data stored in the shift register 34 into a D/A converter. A voltage level similar to the video signal level corresponding to the reflected light, for example, voltage levels Va and Ov shown in FIG. 5, are used as upper and lower reference inputs, respectively. ) is set to output the voltage level ■a, which is the upper limit, while outputting Qv, which is the lower limit, for 0 manual power (all "゛0"), and for the input between the maximum input and the O input. In the case of the white reference generation circuit 30, the voltage between the voltage levels va and Ov is proportionally output at every 1/255 step according to the input bit.
The D/to converter 35 has a voltage level approximately equal to the video signal level corresponding to the light reflected by the white reference plate 14, for example, voltage levels vb and VC (not shown in FIG. 5) as upper and lower reference inputs, respectively. , as above, it is set to output the upper limit voltage level vb for the maximum input of 8 bits, while outputting the lower limit voltage level VC for 0 human power, and for the input between the maximum input and 0 human power. The voltage between the voltage level vb and Vc is 1/255 according to the input pit.
It is designed to be output proportionally for each step.

Next, the quantization process of the video signal will be specifically explained.

In FIG. 2, first, the carriage 20 is moved to the black reference plate 13.
In the process of moving below the white reference plate 14 and then below the white reference plate 14, the video signal via the amplifier 27 becomes, for example, in a state as shown by the solid line in FIG. Here, the black reference value is determined when the video signal level is relatively low, while the white reference value is determined when the video signal level is high.

For example, regarding the process of determining the white reference value, first, the shift register 34 is initialized to 0. While the video signal level is fluctuating between the voltage levels vb and VC, the output of the D/A converter 35 and the voltage divider 36 initially maintain Ov, and the input state of the ROM 33 is set to the mode shown in the attached table. ■It becomes. As a result, the data read from the ROM 33 and stored in the shift register 34 at a predetermined timing is sequentially increased by δ, and the data stored in the shift register 34 corresponds to the voltage level Vc in FIG. When the value exceeds Qv, the output levels of the D/A converter 35 and the voltage divider 36 gradually increase from Qv.

As mentioned above, the output level VO of the D/A converter 35 and the output level ■r of the voltage divider 36 gradually increase, and first, when the output level vO of the D/A converter 35 exceeds the video signal level VV, , the output of the comparator 31 is L level “0”
As a result, the input state of the ROM 33 becomes the mode ■ shown in the attached table.

As a result, the ROM 33 outputs the shift register 3.
The data stored in 4 is decreased by δ, and D
The output level vO of the /A converter 35 also decreases accordingly. On the other hand, as shown above, the output level V of the D/A converter 35
When Q decreases and the output level vO falls below the video signal level Vv again, the input state of the ROM 33 becomes mode (2) again, and the output level (2)0 of the D/A converter 35 increases in the same manner as above.

Then, as the determination process of the mill M quasi-value progresses, the RO
When the input state to the M33 is in mode ■ or ■ repeatedly, and the video signal level VV becomes as shown by the solid line in FIG. 6, the output level VO of the D/A converter 35 changes to The signal level VO approaches the average level. Incidentally, at this time, the output level ``2'' of the voltage divider 36 has a relationship such that the video signal level Vv is sandwiched between the voltage level VO and the voltage level VO, as shown by the dashed line in FIG.

When the voltage levels Vv, Vo, and ■r of the video signal, the output of the D/A converter 35, and the output of the voltage divider 36 are as described above, there is a scratch on the white reference plate 14, Assuming that specular reflection occurs at that position (position Xi in FIG. 6) and the corresponding video signal level becomes extremely high, in this case, the comparators 31 and 32
The outputs of both become H level ``1'', the input state of the ROM 33 becomes mode ■, and the output increases by δ.

That is, even if the video signal level VV rises rapidly, the RO
Since the output of M33 increases only by δ (for example, about 1%), the resulting output level of the D/A converter 35 is 0 and its increase is small (see Fig. 6). Assuming that there is dirt on the white reference plate 14 and the reflection at that position (position x 2 in Fig. 6) suddenly becomes weaker, the corresponding video signal level vvtfi becomes extremely low. The outputs of the devices 31 and 32 both become L level "O11", and when the input state of the ROM 33 becomes mode ■, the output maintains the moe state. That is,
Even if the video signal level VV suddenly increases, the output of the ROM 33 does not change, and therefore the output level vO of the D/A converter 35 also does not change (see FIG. 6).

As mentioned above, the output level VO of the D/A converter 35 is higher than the video signal level VV! l! It does not directly follow the fluctuations in If, but maintains the average level of the video signal level vv. Then, when the carriage 20 reaches a predetermined position, the contents of the shift register 34 are fixed, and the output level of the D/A converter 35 corresponding to the contents of the shift register 34 becomes the white reference value RT.

Further, the process for determining the black reference value is the same as the above process, and even if the black reference plate 13 has a scratch or the like and the corresponding video signal changes rapidly, the output of the D/A converter 35 will change depending on the change. The black reference value Re that is not tracked and is stored also becomes the average level of the video signal level corresponding to the foul light on the black reference plate 13.

As described above, when the carriage 20 moves below the black reference plate 13 and the white reference plate 14, the black reference ++11 RB
When the white reference value RT is determined, when the carriage 20 moves downward to the document 11, the amplifier 27
The video signal V outputted from the circuit is digitally converted by an A/D conversion circuit 50 which uses the white reference value RT and black reference value RB as upper and lower limit reference inputs, respectively. That is, the video signal is quantized.

[Effects of the Invention] As described above, according to the present invention, the average level of the image signal based on the image sensor output corresponding to the white reference plate is taken as the white reference value, and Iζ and the black reference Since the average level of the image signal based on the image sensor output corresponding to the board was used as the black reference value, even if there are scratches, dirt, etc. on each reference board and the image signal at that position changes suddenly, it will not be caused by the fluctuation. As a result, each of the reference values described above does not fluctuate greatly, and the reliability of each of the black and white reference values can be made higher. As a result, more accurate quantization of image signals with less variation becomes possible. Then, the image a (m-point image) created based on the information obtained by the quantization process is made more even and clear. %nei shield i, jCr>r-,'LK=Or>TI%rZ constant 1f
fi f, i)

[Brief explanation of drawings]

Fig. 1 is a diagram of the principle of the present invention, Fig. 2 is a diagram showing an example of an n-horizontal system related to image reading in a system that realizes the image signal hanging system according to the present invention, and Fig. 3 is a diagram showing the stacking system of the present invention. FIG. 4 is a block diagram showing an example of the configuration of the circuit for creating a white reference, FIG. FIG. 3 is a diagram illustrating an example of the operation of the white reference generation circuit. 1... Original 2... Image sensor 3... White reference plate 4... Black reference plate 13... Black reference plate 14... White reference plate 20... Carriage 30... White reference generation circuit 31, 32...Comparator 33...ROM 34...Shift register 35...D/A converter 36...Voltage divider 40...Black reference generation circuit 50... △/D conversion circuit patent applicant: Fujitsu Limited, inventor of the invention (Fig. Incense a'4. Figure 3 Figure 5

Claims (1)

[Claims] An image signal quantization method that quantizes an image signal based on the output of an image sensor (2) when reading a document (1) based on a predetermined white reference value and black reference value. , the predetermined areas (E
1, E2) with the image sensor (2), and the image sensor (2) corresponding to each of the above reference plates (3, 4) is read.
) Average level of image signal based on output (D1, D2)
is extracted, and the average level (
A quantization method for an image signal, characterized in that D1) is the white reference value (A), and an average level (D2) for the black reference plate (4) is the black reference value (B).