JPH06292011A - Picture reader processor - Google Patents

Abstract

PURPOSE:To generate high quality data by converting a signal from an original into a linear electric signal with respect to density, applying A/D conversion to the signal to convert the converted signal into a signal linear to a transmittivity and a reflectance, applying prescribed numerical arithmetic operation processing to the signal and converting the processed signal into a signal linear with respect to density. CONSTITUTION:A signal read from an original with a photoelectric conversion means and linear with respect to a transmittivity and a reflectance is subject to linear logarithmic transformation by a log amplifier of a conversion circuit 12, in which the transformed signal is converted into a signal linear with respect to density. Then the result is A/D-converted by an A/D converter circuit 13 and subject to logarithmic-linear conversion by using a lookup table (LUT) of a conversion circuit 14. Then an arithmetic operation circuit 15 applies prescribed numeric arithmetic operation processing and uses the LUT of the conversion circuit 16 to convert the data into data linear to the density and the result is fed to a post-stage circuit 17. Thus, even when number of bits of the circuit 13 is decreased, sufficient accuracy is obtained by increasing bit number processed by the circuits 14-16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for reading an original surface with an optical sensor (photoelectric conversion element) and processing an electric signal from the optical sensor.

[0002]

2. Description of the Related Art When a document surface is read by an optical sensor such as a CCD and converted into an electric signal to form image data,
Considering human visual characteristics and assuming a multi-gradation printing device as an output medium, image data is often expressed by density (transmission density or reflection density). Here, the transmission density Dt and the reflection density Dr are generally defined as Dt = -logT and Dr = -logR with respect to the transmittance T and the reflectance R, respectively. However, "log" is a common logarithm. C
In an optical sensor such as a CD, the photoelectric conversion signal has a linear relationship with the transmittance T and the reflectance R, so it is necessary to convert the photoelectric conversion signal into density data.

On the other hand, as the image processing performed by this type of apparatus, there are a color correction matrix calculation in a color scanner and a sum of products calculation for correcting a blur component of an optical system or the like. These arithmetic processes must be performed on the data which has a linear relationship with the transmittance or the reflectance.

FIG. 2 is a block diagram showing a conventional example in which both the image processing calculation and the density conversion processing are performed as described above. The electric signal from the photoelectric conversion means 21 is A /
The D conversion circuit 22 performs A / D conversion, and the arithmetic circuit 23 performs image processing calculation (numerical calculation processing). The output from the arithmetic circuit 23 is subjected to density conversion processing using the look-up table 24 and sent to the post-stage circuit 25.

[0005]

In the above conventional example, in order to increase the number of gradations of the density data, the A / D conversion circuit 2
The number of 2 bits must be increased. For example, in order to obtain 256 gradations with density linear data with respect to the maximum density of 3.0, about 16 bits (65536 gradations) are required for transmittance or reflectance linear data. Quantization is required.

An object of the present invention is to provide an image reading processing apparatus capable of forming high-quality data even if the A / D conversion circuit has a small number of bits.

[0007]

An image reading processing apparatus according to the present invention includes photoelectric conversion means for receiving incident light from a document surface and outputting an electric signal corresponding to the incident light quantity, and the photoelectric conversion means for outputting the electric signal. From the A / D conversion circuit, a first conversion circuit that receives a signal that converts the signal into a linear signal with respect to the density, an A / D conversion circuit that A / D converts the signal output from the first conversion circuit, The second which receives the output signal and converts it into a linear signal with respect to the transmittance or reflectance
A conversion circuit, an arithmetic circuit for receiving a signal output from the second conversion circuit and performing a predetermined numerical arithmetic process, and a signal output from the arithmetic circuit for converting the signal into a linear signal with respect to concentration 3 conversion circuits.

[0008]

FIG. 1 is a block diagram showing an embodiment.

The photoelectric conversion means 11 receives incident light from the document surface and outputs an electric signal corresponding to the incident light amount, and is composed of an optical sensor such as CCD and its light receiving circuit.

The conversion circuit 12 converts a signal linear to the transmittance or reflectance of the document surface into a signal linear to the density of the document surface. Specifically, it receives a signal from the photoelectric conversion means 11 and performs linear-logarithmic conversion on the signal, which is configured by a log amplifier or the like.

The A / D conversion circuit 13 A / D converts the logarithmically converted signal. Since the A / D conversion is performed on the logarithmically converted signal, that is, the density linear signal, the number of bits of the A / D conversion can be reduced as compared with the conventional case.

The conversion circuit 14 converts a signal linear with respect to density into a signal linear with respect to transmittance or reflectance. Specifically, it receives data from the A / D conversion circuit 13 and digitally performs logarithmic-linear conversion of the data, which is constituted by a lookup table using a memory. The number of output bits of this conversion circuit 14 is
It is appropriately set according to the accuracy of the arithmetic processing in the arithmetic circuit 15 described later.

The arithmetic circuit 15 receives the data converted into a linear signal with respect to the transmittance or the reflectance by the conversion circuit 14 and performs a predetermined image processing operation (numerical operation processing) as described in the conventional example. ) Is done. The calculation performed by the calculation circuit 15 may be performed by hardware or software.

The conversion circuit 16 converts a signal linear to the transmittance or the reflectance into a signal linear to the density. Specifically, it receives data from the arithmetic circuit 15, digitally performs linear-logarithmic conversion of the data, and sends it to the post-stage circuit 17, which is constituted by a lookup table using a memory. It

Next, the operation of the embodiment shown in FIG. 1 will be described.

In the photoelectric conversion means 11, the reading operation of the document surface is performed by an optical sensor such as CCD. The document surface may be transmissive or reflective. The signal transmitted from the photoelectric conversion means 11 and linear to the transmittance or the reflectance is converted into the conversion circuit 1.
It is linear-logarithmically converted by the log amplifier of No. 2 and converted into a signal linear with respect to the density. The logarithmically converted signal is A / D converted by the A / D conversion circuit 13. A
The D / D-converted data is logarithmically-linearly converted using conversion data preset in the lookup table of the conversion circuit 14, and is linear with respect to the transmittance or the reflectance. Converted to data. The linearly converted data is subjected to predetermined image processing calculation (numerical calculation processing) by the calculation circuit 15.
Is performed. The processed data is converted into a conversion circuit 16
The conversion data preset in the lookup table of
Data is subjected to linear-logarithmic conversion, converted into linear data with respect to the density, and sent to the post-stage circuit 17.

By using the configuration described above, A
Even if the number of bits of the / D conversion circuit 13 is reduced, if the number of bits processed by the conversion circuit 14, the arithmetic circuit 15, and the conversion circuit 16 is increased as necessary, sufficient accuracy (the number of gradations) is obtained.
Is obtained.

[0018]

According to the present invention, it is possible to form high-quality image data even if the number of bits for A / D conversion is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional example.

[Explanation of symbols]

 11 ... Photoelectric conversion means 12 ... 1st conversion circuit 13 ... A / D conversion circuit 14 ... 2nd conversion circuit 15 ... Arithmetic circuit 16 ... 3rd conversion circuit

Claims (2)

[Claims] 1. A photoelectric conversion means for receiving incident light from a document surface and outputting an electric signal corresponding to the amount of the incident light; and a signal output from the photoelectric conversion means to form a linear signal with respect to density. A first conversion circuit for converting, and A / D for A / D converting the signal output from the first conversion circuit.
A D conversion circuit, a second conversion circuit that receives a signal output from the A / D conversion circuit and converts the signal into a linear signal with respect to transmittance or reflectance, and a signal output from the second conversion circuit. An image reading processing apparatus having an arithmetic circuit for receiving and performing a predetermined numerical arithmetic processing, and a third conversion circuit for receiving a signal output from the arithmetic circuit and converting the signal into a linear signal with respect to density. 2. A photoelectric conversion means for receiving incident light from a document surface and outputting an electric signal corresponding to the incident light amount; and a linear converter for receiving a signal output from the photoelectric conversion means.
A first conversion circuit for logarithmic conversion, and A / D for A / D converting the signal output from the first conversion circuit.
Logarithm of the signal output from the D conversion circuit and the A / D conversion circuit
A second conversion circuit for performing linear conversion, an arithmetic circuit for receiving a signal output from the second conversion circuit and performing a predetermined numerical arithmetic process, and a linear-logarithmic conversion for receiving a signal output from the arithmetic circuit An image reading processing device having a 3 conversion circuit.