JPS6323708B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a document reading device that reads images of documents, photographs, drawings, and the like.

Conventional Structure and Problems There is generally a density range (signal level range) unique to a document reading device. In order to read a document with good image quality, it is necessary to match the density range of the document with the density range of the document.

However, conventional document reading devices assume a standard document and manually set the gain, bias, etc. of the signal system at the manufacturing stage to match the density range of the document with the above density range. I'm starting to do that. For this reason, when reading an original whose density range is considerably different from that of a standard original, problems such as image blurring and poor gradation occur.

Furthermore, there are cases in which it is desired to intentionally manipulate the read image quality, but with conventional devices, the only way to do so is to manually adjust the gain and bias of the signal system, which is practically impossible.

Purpose of the invention The present invention solves the above-mentioned conventional problems.
To provide a document reading device capable of reading various documents with high image quality without requiring troublesome adjustment operations, and also capable of arbitrarily changing the read image quality.

Structure of the Invention The present invention automatically normalizes the density read from an original to a density range (image signal level range) specific to the device, and also sets the upper and lower limits of the density range of the original to be normalized using density parameters. The above object is achieved by configuring the document reading device so that the white parameter and the black parameter can be arbitrarily set.

That is _, the document reading device according to the present invention includes means for photoelectrically scanning a document and outputting _an image signal at a level _V , the above image signal and the above density parameters D _W and _DB are input, and the level Vout according to the formula Vout=V ₀ -10 ^DB・V _X /1-10 ^DB-DW (however, V ₀ is a constant value) The invention is characterized in that it has a means for outputting an image signal.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic block diagram of a document reading device according to an embodiment of the present invention. In this figure, reference numeral 1 denotes a document table, on which a document 2 is placed. 3
4 is a laser light source that illuminates the original 2, and 4 is a photo multiplier. The photomultiplier 4 outputs an image signal proportional to the reflectance of the original 2, and this image signal is amplified by a preamplifier 5 and then input to an automatic level set circuit 6.

This automatic level set circuit 6 corrects the level of the image signal so that when a white reference plane with an absolute density of 0 is photoelectrically scanned by the photomultiplier 4, the output _A1 becomes a constant level _V0 over one scanning section. This is a circuit that performs the following. That is, the automatic level set circuit 6 corrects distortions and level fluctuations in the image signal due to variations in the amount of illumination light on the document surface and variations in the sensitivity of the photo multiplier 4. Therefore,
If such image signal distortion and level fluctuations can be ignored, the automatic level set circuit 6 may be omitted.

Reference numeral 7 denotes a density normalization circuit, which is composed of an automatic level control section 8, a parameter processing section 9, and a parameter conversion section 10, the details of which will be described later. Reference numeral 11 denotes an input device for inputting density parameters D _W (white parameter) and D _B (black parameter) to the normalization circuit 7. As this input device 11, for example, a keyboard device is used.

Here, density normalization by the density normalization circuit 7 will be explained with reference to FIG. In this diagram,
V _W is the density specified by the white parameter D _W (D _W )
V B is the image signal level obtained at the output A ₁ of the automatic level set circuit 6 when read by the photo multiplier 4, and V _B is the image signal level when the specified density (D _B ) is read by the black parameter D _B. . The concentration normalization circuit 7 adjusts the voltage between V _W and V B so that V W and V _B match the upper limit level (V ₀ ) and lower limit level (0 volts) of the signal level range (concentration range) unique to the _device , _respectively . The image signal at level _VX (density _DX between _DW and _DB ) is normalized to level Vout.

The arithmetic expression for this normalization will be explained next.

The level of the image signal output from the photo multiplier 4 is proportional to the reflectance of the original, and the relationship between the image signal levels V _W , V _B , V _X and the densities D _W , D _B , D _X is expressed by the formula There are relationships shown in 1, 2, and 3.

V _W =V ₀・10 ^-DW ……1 V _B =V ₀・10 ^-DB ……2 V _X =V ₀・10 ^-DX ……3 In addition, in order to perform the above normalization, It must be established.

_{Vout = V 0 ( V} ^_ _{_} ^DB-DW ... 5. The density normalization circuit 7 performs normalization by calculating Equation 5. However, as will be described later, the density normalization circuit 7 in this embodiment is configured to execute Equation 6, which is equivalent to Equation 5.

Vout=(V ₀ −10 ^DB・V _X /10)・(10/1−10 ^DB−DW ) ……6 FIG. First, the parameter conversion section 10 will be described. Reference numerals 18 and 19 are latch circuits, 20 is a subtraction circuit, and 21 and 22 are bus interfaces.
The latch circuits 18 and 19 are connected to the input device 11 (first
The black parameter input in 8-bit parallel from
D _B and white parameter D _W are respectively latched. The subtraction circuit 20 includes latch circuits 18 and 19.
Black parameter D _B and white parameter input from
Find data on the difference between D _W (D _B −D _W ). This data (D _B −D _W ) is sent to the parameter processing section 9 via the bus interface 22. In addition, the black parameter latched in the latch circuit 18
D _B is input as is to the parameter converter 9 via the bus interface 21 .

The parameter conversion section 9 is composed of a conversion ROM 23 and latch circuits 24 and 25. The conversion ROM 23 works as a logarithmic converter, and the parameter conversion section 10
Using the input data as the address, output data (-10 ^DB /10) for the black parameter D _B , and output data (10 ^DB-DW -1) for the data (D _B - D _W ). Output. The former data (−
10 ^DB /10) is latched in the latch circuit 25, and the latter data (10 ^DB-DW -1) is latched in the latch circuit 24.

Note that inside the parameter processing section 9 and the parameter conversion section 10, all data is treated as 8-bit parallel data.

The automatic level control section 8 uses the image signal inputted from the automatic level set circuit 6 (FIG. 1) and the data inputted from the parameter processing section 9.
It executes the normalization calculation of Equation 6 above and sends the normalized image signal to the output _A2 , and its configuration will be described below.

26 is an operational amplifier whose non-inverting side input is grounded via a resistor 27, and whose inverting side input is connected via a resistor 28 to the automatic level set circuit 6 (first
It is connected to the output A ₁ of FIG. The resistance value of the resistance switching circuit 29 is the data output from the latch circuit 25 (-10 ^DB /10)
The image signal inputted from the automatic level set circuit 6 is multiplied by (-10 ^DB /10) and the signal is outputted to the operational amplifier 26.
It is output from

Reference numeral 30 denotes an operational amplifier, which is subjected to negative feedback by resistors 31 and 32 so as to function as an amplifier with a voltage amplification factor of 1. A constant voltage V ₀ /10 is applied by a voltage source 33 to the inverting input of the operational amplifier 30, and the non-inverting input is coupled to the output of the preceding operational amplifier 26. Therefore, the signal output from the operational amplifier 26 has a constant voltage V ₀ /
Signal obtained by adding 10, i.e. (V ₀ −10 ^DB・V _X )/10
A signal with a level of 0 is obtained at the output of the operational amplifier 30.

34 is an operational amplifier, the non-inverting side input is grounded via a resistor 35, and the inverting side input is coupled to the output via a resistor 36. In addition, the inverting side input is the output data of the latch circuit 24 (10 ^DB-DW −1)
It is connected to the output of the preceding operational amplifier 30 via a resistance switching circuit 37 whose resistance value changes stepwise according to the resistance value. The output of the operational amplifier 34, that is, the output _A2 of the concentration normalization circuit 7, is connected to the operational amplifier 3.
0 output signal multiplied by 10/(1-10 ^DB-DW ),
That is, the image signal normalized by the above equation 6 is output.

FIG. 4 is a circuit diagram of the resistance switching circuits 29 and 37. In this figure, eight resistors 40 to 47 are connected in series between terminals 38 and 39;
A relay 48 is connected to each of these resistors 40 to 47.
55 contacts 48a to 55a are connected in parallel. 56-63 are drivers for relays 48-55, and 8-bit data input from terminal 64 (output data of latch circuit 24 or 25)
According to the state of the corresponding bit, the corresponding relays 48 to 55 are driven to close the contacts 48a to 55a.
By turning on/off the terminals 38, 39
Switch the resistance value between.

When reading a document using the document reading device described above, the operator first needs to set the density parameters.
D _W and D _B are input from the input device 11. The values of the density parameters D _W and D _B can be arbitrarily determined depending on what kind of image quality is required. For example, if you want to faithfully read the density of a document, measure the density of the whitest and blackest parts of the document, and set the white parameter to the value corresponding to the density of the former.
Enter D _W and enter the black parameter D _B with a value corresponding to the density of the latter. Then, the image signal obtained by photoelectric scanning of the original is normalized by the density normalization circuit 7 so that it is faithfully reproduced over the entire original density range. In this way, by appropriately determining the values of the density parameters D _W and D _B depending on the document, various documents can be read with good image quality.

If you want to read a document with blurred image quality, input a black parameter D _B with a value corresponding to a density lower than the density of the blackest part of the document. In this way, the image signal is normalized to be biased toward black, so that it is possible to read an image with a slightly blurred appearance. On the other hand, if you want an image quality that is a little blurred, you can input the white parameter D _W with a value corresponding to a higher density than the whitest part of the document and normalize the image signal toward white.

Similarly, the read image quality can be varied in various ways by selecting the values of the white parameter D _W and the black parameter D _B.

Note that the density normalization circuit 7 of the above embodiment is based on equation 5.
Although normalization is performed by calculating Equation 6 which is a modified version of Equation 6, it is also possible to perform Equation 5 itself or another equivalent modified form.

In addition, in the above embodiment, the photoelectric scanning of the document is performed using the photomultiplier 4, but the CCD
Other imaging devices such as image sensors may also be used.

Furthermore, a densitometer can also be used as the input device 11.

Effects of the Invention As described above, the document reading device according to the present invention includes means for photoelectrically scanning a document and outputting an image signal at a level proportional to the reflectance of the document, and means for inputting a density parameter having an arbitrary value. Since the image signal is normalized according to the density parameter, the density parameter can be set to an appropriate value without the need for troublesome operations such as manually adjusting the gain and bias of the signal system as in the past. By simply inputting , various originals with different density ranges can be read with good image quality, and the read image quality can also be varied in various ways.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a document reading device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of normalization, FIG. 3 is a detailed block diagram of a density normalization circuit, and FIG. 4 is a diagram of a resistance switching circuit. FIG. 3 is a circuit configuration diagram. DESCRIPTION OF SYMBOLS 1... Original table, 2... Original, 3... Laser light source, 4... Photo multiplier, 5... Preamplifier, 6... Automatic level set circuit, 7... Density normalization circuit, 11... input device.

Claims (1)

_[ Scope of Claims] 1. Means for photoelectrically scanning a document and outputting an image signal at a _{level V}
The above image signal and the above density parameters D _W and _DB are input, and the image signal has a level Vout that satisfies Vout = V ₀ -10 ^DB・V _X /1-10 ^DB-DW (however, V ₀ is a constant value) A document reading device comprising means for outputting.