JPH03219776A - Picture signal processor - Google Patents

Abstract

PURPOSE:To attain a proper multi-level processing in response to the density distribution of an original picture by forming a density histogram from an analog electric signal representing picture information and selecting a read density range of the picture from the histogram. CONSTITUTION:A light from an LED array 23 is reflected in an original S and radiates to a sensor 22 via a rod lens array 21. The sensor 22 generates an output in response to the radiating light and inputs it to an A/D converter 203 via an amplifier 202. The converter 203 compares an output of the amplifier 202 with a reference value set initially and converts the result into an 8-bit digital value. The converted picture data is stored in a RAM 209 and a CPU 207 generates a histogram. When the read picture data does not appear a reference level B0 being a bright level as shown in separate figure, a level of a 2nd D/A converter 205 is reset from B0 to Dx (in this case B2) so that the density range from A0 to B2 is able to be converted into an 8-bit digital value by the converter 203.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an image signal processing device.

[Prior Art] Conventionally, in an image signal processing device in which a document image is sampled pixel by pixel by an image sensor and the sampled output is subjected to multi-value processing in a control unit, analog/digital conversion is performed in the control unit. The image sensor output is compared with a reference voltage using an A/D converter (hereinafter referred to as an A/D converter), and multi-value processing is performed within a predetermined density range.

2) The image signal processing apparatus according to claim 1, wherein the setting means controls the reference comparison voltage when setting the density range.

[Problem to be solved by the invention] However, in the device configured in this way,
Even if the original image has a skewed density distribution centered around a certain density, multi-value processing is always performed within a certain density range, so there is a drawback that the original image cannot be read as a signal with sufficient gradation. Ta.

Furthermore, if there is not much difference in density between the background of the original image and the characters, etc., there is a drawback that it is difficult to distinguish between the background and the characters when multi-value processing is performed.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide an image signal processing device that enables appropriate multi-value processing depending on the density distribution of a document.

[Means to solve the problem]

The image signal processing according to the present invention includes a conversion means that receives an image analog signal and obtains a digital signal by comparing the analog signal with a reference comparison voltage, and an operation that forms a density histogram based on the digital signal. means and
and setting means for setting an image reading density range with reference to the density histogram.

[Function J] According to the present invention, a density histogram is formed from an analog electrical signal representing image information, and the optimum density range for the original image is set by selecting the reading density range of the image once from the histogram. I can do it.

〔Example〕

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

FIG. 1 is a cross-sectional configuration diagram of a document image reading device to which the present invention is applied. The image reading device 1, as shown in FIG.
The body 2 has a contact type image sensor 3 (21: rod lens array, 23: LED array, 22: sensor), and a sheet document S is placed under the sensor 3.
It has a reading roller 5 that presses against the sensor 3. and,
A sheet discharging device 6 is disposed downstream of the reading sensor 3, and the discharging device 6 includes a sheet discharging roller 9 that constitutes the inner guide surface of the reversing path 12, and a sheet discharging roller 9 that comes into contact with the roller 9. It has a flexible clamping plate 10 made of a plate spring that clamps and discharges S.

Further, a paper ejection port 1 is provided in the machine body 2 in the horizontal direction of the holding plate 10.
1 is opened, and furthermore, a paper discharge port 13 is opened in the body above the paper discharge roller 9.

First, the operation of the document image reading device will be explained using the block diagrams shown in FIGS. 1 and 2.

The document reading device (hereinafter referred to as a scanner) according to this embodiment is always an external device (digital printer).

communication of control signals with these external devices and image output to the external devices are performed via the interface circuit 210.

The CPU 207 has the first D/A converter 2 in advance.
08 (for dark level reference value):! 3 and the second D/A converter 205 (for bright level reference value) to perform initial settings. When a document reading start command is input from an external device in this state, the sheet document S is conveyed from upstream, and rotation from a motor (not shown) is transmitted to the reading roller through a drive gear (not shown). 5 and the reading sensor 3 and conveyed to the paper discharge roller 9.

At this time, the image analog signal read by the sensor 22 in the reading sensor 3 is amplified by the amplifier 202 and input to the A/D converter 203.

The AID converter 203 converts the image signal into an 8-bit digital signal. This digital signal is supplied to the binarization circuit 204, and the 2
The 8-bit digital image signal is binarized using the digitization threshold and converted into a 1-bit digital image signal.

206 is a selector which selects an 8-bit multi-value digital image signal and a 1-bit digital image signal according to a control signal output from the CPU 207
Select either one of the bit binarized digital image signals and send it to the interface circuit 210.
Output to external device.

Next, the operation of this embodiment will be explained using FIG. 2, FIG. 3(a) to FIG. 3(d), and FIG. 4.

FIG. 4 is a flowchart showing the processing procedure for setting the reference value of the A/D converter 203 in this embodiment.

In FIG. 4, in step 401, the CPU 207 connects the first D/A converter 208 (for dark level reference voltage).
, a reference value (AO: reflectance 0) predetermined in the second D/A converter 205 (for bright level reference voltage)
% value, Bo: value of 100% reflectance).

Subsequently, in step 402, the light from the LED array 23 is first reflected by the document S, and is irradiated onto the sensor 22 via the rod lens array 21.

The sensor 22 generates an output according to the irradiated light,
The signal is input to an A/D converter 203 via an amplifier 202.

The A/D converter 203 compares the output of the amplifier 202 with an initially set reference value and converts it into an 8-bit digital value. The converted image data is stored in the RAM 209 in step 403, and the CPU 207 creates a histogram.

Next, steps 404 and 405 will be specifically explained.

Now, if the histogram of the read image data does not appear up to the bright level reference value B0 as shown in FIG.
88 (in this case, B), and the concentration range from 80 to 82 is converted to an 8-bit digital value by the A/D converter 203.
Make it possible to convert with .

Further, as shown in FIG. 3(c), when the read image data does not appear up to the dark level reference individual 0, the value of the first D/A converter 208 is changed to Ao-A- (here, A, ) and convert the density range from A3 to 80 into an 8-bit digital value.

Similarly, in the case of FIG. 3(d), the bright level reference value B
0→B4. By changing the dark level reference value from A0 to A4, the A/D conversion range can be selected.

Other Examples 11 In the above embodiment, a configuration was adopted in which A/D conversion could be performed in all the density ranges that occur.
) As shown in the density histogram shown in Figure 2, for an image consisting only of the background and characters, reference values (AO-'AI, BO-'Bl) are set near the thresholds of the background and characters.
), it is possible to easily identify characters, etc. against the background.

[Effects of the Invention] As explained above, according to the present invention, a density histogram is formed from an analog electrical signal representing image information, and the reading density range of an image can be selected from the histogram. Set the concentration range,
Appropriate multivalue processing according to the density distribution of the original image becomes possible.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional configuration diagram of an image reading device according to an embodiment of the present invention, FIG. 2 is a block diagram of the image reading device, and FIGS.
FIG. 3(d) is a diagram showing an example of a density histogram, and FIG. 4 is a flowchart showing the operation of this embodiment. 1... Image reading device, 2... Machine body, 3... Contact type image sensor, 5... Reading roller, 6... Sheet ejecting device, 9... Paper ejecting roller, lO... Holding plate, 11... Paper discharge port, 12... Reverse path, 13... Paper discharge port, 21... Rod lens, 22... Sensor, 23... LED array, 202... Amplifier, 203... A/D converter, 204... Binarization circuit, 205... D/A converter (B) (for bright level reference value), 206... Selector, 207... CPU , ...D/A converter (A) (for dark level reference value) ...RAM ...I/F circuit. Diagram

Claims (1)

[Scope of Claims] 1) Conversion means for obtaining a digital signal by inputting an image analog signal and comparing the analog signal with a reference comparison voltage; and a calculation means for forming a density histogram based on the digital signal. An image signal processing apparatus comprising: a setting means for setting an image reading density range by referring to the density histogram. 2) The image signal processing apparatus according to claim 1, wherein the setting means controls the reference comparison voltage when setting the density range.