JP2585925B2 - Image reading processor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus 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 image data is formed by reading a document surface with an optical sensor such as a CCD and converting it into an electric signal,
In consideration of human visual characteristics and assuming a multi-gradation printing device as an output medium, image data is often represented 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. Here, “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. Therefore, it is necessary to convert the photoelectric conversion signal into density data.

On the other hand, image processing performed by this type of apparatus includes a color correction matrix operation in a color scanner and a product-sum operation for correcting a blur component of an optical system or the like. These computations must be performed on data that has a linear relationship with the transmittance or reflectance.

FIG. 2 is a block diagram showing a conventional example in which both image processing operation and density conversion processing are performed as described above. The electric signal from the photoelectric conversion means 21 is A /
A / D conversion is performed by the D conversion circuit 22, and image processing calculation (numerical calculation processing) is performed by the calculation circuit 23. The output from the arithmetic circuit 23 is subjected to density conversion processing using a look-up table 24, and sent to a 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 is used.
The number of bits of 2 must be increased. For example, in order to obtain 256 gradations with data linear in density with respect to the maximum density of 3.0, about 16 bits (65536 gradations) for data linear in transmittance or reflectance. Quantization is required.

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

[0007]

Means for Solving the Problems Image reading in the present invention
The processing unit receives incident light from the original surface and
Photoelectric conversion means for outputting a first signal corresponding to the conversion signal;
In response to the first signal output from the photoelectric conversion means,
Perform a logarithmic conversion to obtain a second signal that is linear with respect to the density.
A first conversion circuit for outputting, and an output from the first conversion circuit.
A / D converting the second signal to be output and outputting a third signal
A D conversion circuit, and a third output from the A / D conversion circuit.
Receiving the signal, log-linear conversion is performed and the transmittance or
A second conversion circuit that outputs a fourth signal that is linear with respect to the emissivity
Receiving the fourth signal output from the second conversion circuit
And an arithmetic circuit for performing predetermined numerical operation processing.

Further, a fifth output from the arithmetic circuit is provided.
A third conversion circuit for receiving a signal and performing linear-logarithmic conversion is provided.
You may.

[0009]

FIG. 1 is a block diagram showing an embodiment.

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

The conversion circuit 12 converts a signal that is linear with respect to the transmittance or reflectance of the document surface into a signal that is linear with respect to the density of the document surface. More specifically, it receives a signal from the photoelectric conversion means 11 and performs a linear-logarithmic conversion of the signal, and is constituted 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 signal having a linear density, the number of bits of the A / D conversion can be reduced as compared with the related art.

The conversion circuit 14 converts a signal that is linear with respect to density into a signal that is 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, and is configured by a look-up table or the like using a memory. The number of output bits of the conversion circuit 14 is
It is set appropriately according to the accuracy of the arithmetic processing in the arithmetic circuit 15 described later.

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

The conversion circuit 16 converts a signal linear in transmittance or reflectance into a signal linear in density. More specifically, it receives data from the arithmetic circuit 15, converts it digitally to linear-logarithmic conversion, and sends it to the post-stage circuit 17, which is composed of a look-up table using a memory or the like. You.

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

In the photoelectric conversion means 11, the reading operation of the original surface is performed by an optical sensor such as a CCD. The document surface may be a transmission type or a reflection type. A signal linearly transmitted or reflected from the photoelectric conversion means 11 is transmitted to the conversion circuit 1.
The signal is linear-logarithmically converted by a log amp 2 and converted to a signal linear with respect to density. The logarithmically converted signal is A / D converted by the A / D conversion circuit 13. A
The data subjected to the / D conversion is logarithm-linearly converted using conversion data preset in a look-up table of the conversion circuit 14, and data linear with respect to transmittance or reflectance. Is converted to The linearly converted data is subjected to a predetermined image processing operation (numerical operation processing) by the operation circuit 15.
Is performed. The processed data is supplied to the conversion circuit 16.
Conversion data preset in the lookup table
The data is subjected to a linear-logarithmic conversion using data, is converted to data linear with respect to the density, and is 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.

[0019]

According to the present invention, the output from the photoelectric conversion means is provided.
A using the second signal obtained by linear-logarithmically converting the first signal
A / D conversion reduces the number of A / D conversion bits
And a third signal output from the A / D conversion circuit.
The logarithm-linear conversion of
Since the numerical operation processing is performed using the near fourth signal, A /
High quality image data even if the number of D conversion bits is reduced
It can be formed.

[Brief description of the 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 first conversion circuit 13 A / D conversion circuit 14 second conversion circuit 15 arithmetic circuit 16 third conversion circuit

 ────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-60-216350 (JP, A) JP-A-61-39776 (JP, A) JP-A-62-183673 (JP, A)

Claims (2)

(57) [Claims] And a photoelectric conversion unit for receiving incident light from a document surface.
Photoelectric conversion means for outputting a first signal corresponding to the conversion signal;
Perform a logarithmic conversion to obtain a second signal that is linear with respect to the density.
A first conversion circuit for outputting, and A / D conversion of a second signal output from the first conversion circuit
An A / D converter circuit for outputting a third signal by, pair receives the third signal output from the A / D converter circuit
Perform a number-to-linear conversion and reset the transmittance or reflectance.
An image reading processing device comprising: a second conversion circuit that outputs a near fourth signal; and an arithmetic circuit that receives the fourth signal output from the second conversion circuit and performs a predetermined numerical operation. 2. Receiving incident light from a document surface and subjecting the light to photoelectric conversion
Photoelectric conversion means for outputting a first signal corresponding to the conversion signal;
Perform a logarithmic conversion to obtain a second signal that is linear with respect to the density.
A first conversion circuit for outputting, and A / D conversion of a second signal output from the first conversion circuit
An A / D converter circuit for outputting a third signal by, pair receives the third signal output from the A / D converter circuit
Perform a number-to-linear conversion and reset the transmittance or reflectance.
A second conversion circuit that outputs a near fourth signal, an arithmetic circuit that receives the fourth signal output from the second conversion circuit and performs a predetermined numerical operation, and a fifth signal that is output from the arithmetic circuit. An image reading processing device having a third conversion circuit for receiving and linear-logarithmically converting the received data.