JPH08116438A - Output correction device for image sensor - Google Patents

Abstract

PURPOSE: To reduce cost by adopting the configuration such that an output is corrected even without a high speed divider. CONSTITUTION: An A/D converter 4 is used to convert analog picture element data of an image sensor 1 into digital picture element data, a storage means 5 stores in advance at least a white reference level corresponding to a picture element address of the sensor 1, a storage means 6 stores a correction image signal based on at least the white reference level and the digital picture element data, a synchronization address generating means 8 generates an address synchronously with a picture element address of the sensor 1 and the storage means 5 generates at least the white reference level corresponding to the synchronization address, then the storage means 6 provides an output of a correction image signal corresponding to the white reference level corresponding to the synchronization address from the storage means 5 and actual digital picture element data from the A/D converter 4 so as to correct the output even without a high speed divider.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output correction device for an image sensor such as a line sensor or an area sensor.

[0002]

2. Description of the Related Art When a document is read by an image sensor, the image signals at both ends of the sensor generally become dark.
A device for correcting the output (shading correction) is required. The output correction device of this image sensor is
Before performing the output correction, as shown in FIG. 4, a black level (sensor dark level when the light source is cut off) output from a line sensor (area sensor) 1 including, for example, a CCD (Charge Coupled Device), etc. ) And a white level are calculated for each pixel bit by the reference level generating means 12, these are stored in the black memory 13 and the white memory 14, respectively, and a black reference level and a white reference level are generated (see FIG. 5). At the time of actual output correction, the output (brightness) is corrected by performing a correction calculation by the high-speed divider 15 using the reference level and the actual pixel data from the line sensor 1.

[0003]

However, the output correction device for the image sensor has the following problems. That is, in order to perform the correction calculation, the high speed divider 15
However, since the high-speed divider 15 is expensive, there is a problem that the entire device is expensive.

In such an output correction device for an image sensor, a so-called gamma (γ) correction is often required as a contrast correction for enhancing the visibility. Gamma correction cannot be performed with the correction using 15. Therefore, there is a problem that a new gamma correction device must be provided.

Therefore, it is a first object of the present invention to provide an output correction device for an image sensor, which can perform output correction without a high-speed divider and can reduce costs.

Further, in addition to the above first object, the present invention has a second object to provide an output correction device for an image sensor which can perform gamma correction without newly providing a device for gamma correction. To do.

[0007]

In order to achieve the first object, an output correction device for an image sensor according to a first means is an A / D converter for converting analog pixel data of the image sensor into digital pixel data. A sync address generating means for generating an address in synchronization with a pixel address of the image sensor, and at least a white reference level of a white and a black reference level corresponding to the pixel address of the image sensor are stored in advance, and according to the synchronization address. First storage means for outputting at least a white reference level of the white and black reference levels corresponding to this synchronization address, and a corrected image signal based on at least the white reference level of the white and black reference levels and the digital pixel data are stored in advance. The digital pixel data from the A / D converter and the same from the first storage means. In accordance with at least the white reference white level and black reference level corresponding to the address, equipped with second memory means for outputting a corrected image signal corresponding to these, the.

In order to achieve the second object, the image sensor output correction device of the second means includes, in addition to the first means, correction image signals stored in advance in the second storage means, The feature is that gamma correction is performed to improve visibility.

[0009]

According to the output correction device of the image sensor in the first means, the analog pixel data of the image sensor is converted into the digital pixel data by the A / D converter, but in the first storage means, At least a white reference level of white and black reference levels corresponding to the pixel address of the image sensor is stored in advance, and in the second storage means, a corrected image based on at least the white reference level of the white and black reference levels and the digital pixel data. A signal is stored in advance, and an address synchronized with the pixel address of the image sensor is generated by the synchronization address generation means, and at least the white reference of the white and black reference levels corresponding to this synchronization address is generated by the first storage means. When the level is output, the second storage means corresponds to the synchronization address from the first storage means. And according to actual digital pixel data from at least the white reference level and A / D converter of the black reference level, the output corrected image signals corresponding to these, so that the output correction is made without the high-speed divider.

Further, according to the output correction device of the image sensor in the second means, the gamma correction for enhancing the visibility is performed by the corrected image signal stored in the second storage means in advance, and the gamma correction is performed. No additional equipment is required.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of an image sensor output correction apparatus according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a line sensor composed of, for example, a CCD or the like, and the line sensor 1 reads an original document in accordance with a clock from a clock generator 2. An amplifier 7 that amplifies the output of the line sensor 1 is connected to the line sensor 1. The amplifier 7 converts the amplified analog pixel data into 8-bit digital pixel data and outputs the digital pixel data. The A / D converter 4 is connected.

An address counter 3 for counting addresses is also connected to the clock generator 2, and a first storage means 5 is connected to the address counter 3. Therefore, an address synchronized with the pixel address of the line sensor 1 is input to the first storage means 5. That is, when the line sensor 1 outputs pixel data of the 100th pixel, for example,
The address of the 100th pixel is input to the storage means 5.

The first storage means 5 comprises, for example, a RAM, and the white reference level corresponding to the pixel address of the line sensor 1 is stored in advance. Thus, for example, pixel 1
When the address 00th is input, this pixel 10
The 0th white reference level is output as an 8-bit white reference level, for example.

The A / D converter 4 and the first storage means 5
Is connected to a second storage means 6 composed of, for example, a ROM, and the 8-bit output line of the A / D converter 4 is connected to, for example, lower addresses A ₀ and A _{1 of} the second storage means 6. A ₇
The 8-bit output line of the first storage means 5 is connected to, for example, the upper addresses A ₈ and A _{9 to} A ₁₅ of the second storage means 6, respectively. Therefore, the A / D converter 4 and the first
The storage means 5 can specify 2 ¹⁶ = 65536 kinds of addresses. The upper and lower addresses may be reversed.

The second storage means 6 stores in advance a corrected image signal based on the white reference level and the digital pixel data. The corrected image signal is obtained by previously storing the calculation result obtained by substituting the white reference level and the digital pixel data into the equation 1.

[Equation 1]

The output enable pin of the second storage means (ROM) 6 is always low. Therefore, when the 8-bit actual digital pixel data is input from the A / D converter 4 and the 8-bit white reference level of the address synchronized with the digital pixel data is input from the first storage means 5, respectively. From the 8-bit data lines D _{0 to} D _{7 of the} second storage means 6, the corrected image signals stored in advance according to the digital pixel data and the white reference level are output.

Thus, in this embodiment, the A / D
The converter 4 converts the analog pixel data of the line sensor 1 into digital pixel data, and the first storage means 5
The white reference level corresponding to the pixel address of the line sensor 1 is stored in advance, the second storage unit 6 stores the corrected image signal based on the white reference level and the digital pixel data in advance, and the clock generator 2 and the address are stored. When the synchronous address generating means 8 including the counter 3 generates an address synchronized with the pixel address of the line sensor 1 and the first storage means 5 outputs the white reference level corresponding to the synchronous address, the second reference level is output. According to the white reference level corresponding to the synchronization address from the first storage means 5 and the actual digital pixel data from the A / D converter 4, the storage means 6 outputs corrected image signals corresponding to these. Since it is configured, it is possible to correct the output without a high-speed divider, and thus it is possible to reduce the cost.

Although the first storage means 5 is a RAM in the above embodiment, it may be replaced with a ROM. However, in this case, since the sensitivity of the CCD gradually changes with time and the light amount of the LED also decreases, it is possible to rewrite the white reference level, for example, PROM (programmable ROM) or EPROM (erasable PRO).
M) is preferred.

The second storage means 6 can also be a RAM instead of a ROM.

Further, in the above embodiment, the parameters of the corrected image signal are the white reference level and the digital pixel data, but the black reference level can be added to further improve the correction accuracy. In this case, the second
The corrected image signal stored in advance in the storage means 6 is calculated by Equation 2.

[Equation 2]

In the output correction device for the line sensor, so-called gamma (γ) correction is often required as the contrast correction for enhancing the visibility. As this gamma correction, for example, it is known that the difference in white is comparatively invisible to the naked eye, and therefore bright and dark are provided so that the difference can be seen.

However, the prior art fast divider 15
In the corrected image signal according to (1), the relationship between (pixel data) / (white level) and the corrected image signal V _sig is a linear function as indicated by the alternate long and short dash line Y in FIG.
For example, when (pixel data) / (white level) approaches 0 (becomes black), the corrected image signal V _sig approaches 0, and when (pixel data) / (white level) becomes 1, the corrected image signal V _sig
Is 256 (8-bit gradation), but in the present embodiment, the above-mentioned gamma correction function is added to the corrected image signal V _sig stored in advance in the second storage means 6, It corresponds to the function indicated by the solid line X.

That is, for example, when (pixel data) / (white level) approaches 0, the corrected image signal V _sig is at the lower limit value 10, and when (pixel data) / (white level) is 1, the corrected image signal V _sig is 1. the V _sig upper limit 248, the corrected image signals V _sig to be respectively and therebetween a curve corresponding is set, moreover (pixel data) / (white level)
When the value exceeds 1 by a predetermined value or more (when a mirror or the like is totally reflected to exceed the white reference level by a predetermined value or more; in a region W shown in FIG. 5), the corrected image signal V _sig is The setting is made so that the lower limit value 10 (that is, black) is output, and therefore, the contrast of black is added to a place where the difference in white is unknown, and the visibility is improved.

FIG. 3 shows an example in which another gamma correction function is added to the corrected image signal V _sig stored in advance in the second storage means 6, and the second image shown in FIG. The black and white of the corrected image signal stored in advance in the storage means 6 is inverted. In this case, the corrected image signal stored in advance in the second storage unit 6 is calculated by Equation 3.

(Equation 3)

As described above, in this embodiment, the corrected image signal stored in advance in the second storage means 6
Since the gamma correction for enhancing the visibility can be performed (arbitrary correction can be performed), the gamma correction can be performed without newly providing a gamma correction device.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say, for example, in the above embodiment, the line sensor is used as the image sensor, but it goes without saying that the same can be applied to the area sensor.

The gradation is not limited to 8 bits and may be 4 bits, 16 bits or the like.

[0029]

As described above, according to the output correction device for an image sensor of the first invention, the A / D converter
The analog pixel data of the image sensor is converted into digital pixel data, at least the white reference level of the white and black reference levels corresponding to the pixel address of the image sensor is stored in advance in the first storage means, and the second storage means A corrected image signal based on at least the white reference level of the white and black reference levels and the digital pixel data is stored in advance, and an address synchronized with the pixel address of the image sensor is generated by the synchronization address generation means to generate the first image. When at least the white reference level of the white and black reference levels corresponding to the synchronization address is output by the storage means, the second storage means outputs the white and black reference levels corresponding to the synchronization address from the first storage means. Correspond to at least the white reference level and the actual digital pixel data from the A / D converter Outputs a positive image signal, from those configured to allow the even output correction without high speed divider, it is possible to reduce the cost.

According to the output correction device for an image sensor of the second invention, in addition to the first invention, the gamma correction for enhancing the visibility is made possible by the corrected image signal previously stored in the second storage means. Therefore, it is possible to perform gamma correction without newly providing a device for gamma correction.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an output correction device for an image sensor according to an embodiment of the present invention.

[FIG. 2] Same as above (pixel data) / (white level) when the output correction device of the image sensor has a gamma correction function
FIG. 7 is a diagram showing an example of the relationship between the image signal and the corrected image signal in comparison with a conventional technique having no gamma correction function.

[FIG. 3] Same as above (pixel data) / (white level) when the output correction device of the image sensor has a gamma correction function
It is a figure showing the other example of the relationship between and a corrected image signal.

FIG. 4 is a block diagram showing the overall configuration of an image sensor output correction device in the related art.

FIG. 5 is a schematic explanatory diagram for explaining a region in the case of generating a black reference level and a white reference level and performing total reflection.

[Explanation of symbols]

 1 Image Sensor 4 A / D Converter 5 First Storage Means 6 Second Storage Means 8 Synchronous Address Generation Means

Claims (2)

[Claims] 1. An A / D converter for converting analog pixel data of an image sensor into digital pixel data, a synchronous address generating unit for generating an address synchronized with a pixel address of the image sensor, and a pixel address of the image sensor. First storage means for storing at least a white reference level of the white and black reference levels corresponding to, and outputting at least a white reference level of the white and black reference levels corresponding to the synchronization address according to the synchronization address; And a corrected image signal based on at least the white reference level of the black reference level and the digital pixel data are stored in advance, and the digital pixel data from the A / D converter and the synchronization address from the first storage means are stored. Corresponding to at least white reference level of white and black reference level An output correction device for an image sensor, comprising: a second storage unit that outputs a corrected image signal. 2. The output correction device for an image sensor according to claim 1, wherein the corrected image signal stored in advance in the second storage means is gamma-corrected to improve visibility. Image sensor output correction device.