JPH03184471A - Picture reader - Google Patents

Abstract

PURPOSE:To obtain the gradation of contrast from the original of the low contrast by providing a level converting means to input the output of a quantizing means and to output it while converting to a prescribed correspondent relation and a control means to set the correspondent relation of conversion at the level converting means corresponding to the range of a quantizing density level to be obtained from a detecting means. CONSTITUTION:For multilevel quantized data, appearance frequency (density histogram) for each density is counted by an adder 7 and stored in a histogram memory 8. After this prescanning, a CPU 11 outputs a conversion table to a conversion table memory 10 by referring the contents of the histogram memory 8. Next, a switch 6 is changed over to a transformer 9 side and scanning is executed for outputting picture signals. In such a case, the multilevel quantized data are inputted from an A/D conversion part 2 to the transformer 9 and according to the conversion table in the conversion table memory 10, level conversion is executed. Then, the data are outputted after executing a gradation processing such as a dither processing, etc., by a gradation processing part 5.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an image reading device that scans and exposes an original image and converts it photoelectrically with an image sensor, and particularly relates to a device that reads gradation images such as photographs.

[Conventional technology]

2. Description of the Related Art Conventionally, image reading devices using image sensors such as CCDs have been provided.

FIG. 1f shows a block diagram of this type of image reading device. In this figure, an imaging unit 1 using an image sensor such as a CC port photoelectrically converts reflected light from a document placed on a document table or projected light from a microfilm while scanning it, and converts it to/D. Multi-level quantization is performed by unit 2.

This multilevel quantized data is supplied to the next gradation processing section 5,
The data is converted into Ilo binary data that can reproduce a gradation image using a dither method or the like, and is output from a reading device.

(Problem to be Solved by the Invention) In such a conventional example, even an original with low contrast is read faithfully, so when the output data is reproduced, the contrast is weak like that of the original. There was a point.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image reading device that can obtain high contrast gradation from a low contrast original without impairing the gradation of the original.

[Means to solve the problem]

An image reading device according to the present invention is an image reading device that scans and exposes a document image and performs photoelectric conversion using an image sensor, and includes a quantization unit that converts an image density signal obtained by scanning into density level values in multiple stages. , a detection means for detecting a range of quantized density levels obtained from the quantization means; a level conversion means for inputting the output of the quantization means, converting it into a predetermined correspondence relationship and outputting it; and control means for setting the correspondence of conversion in the level conversion means according to the range of quantized density levels.

Further, in an image reading device that scans and exposes a document image and charges and converts it with an image sensor, a quantization unit that converts an image density signal obtained by scanning into a plurality of density level values, and a an adding means for calculating the appearance frequency for each quantization density level; a level converting means for inputting the output of the quantization means, converting it into a predetermined correspondence relationship and outputting it; and a quantization density level obtained from the addition means. It is also possible to adopt a configuration including a control means for setting a correspondence relationship of conversion in the level conversion means according to the frequency of appearance of each level conversion means.

[For production]

In order to solve the above-mentioned problems, the present invention uses an addition means for calculating the appearance frequency of each quantization concentration level from the quantization means, or detects the range of quantization concentration levels from the quantization means. Detection hand! 4) )-, $4i1a
-i”2 rbtM 'iL G '2!' 1h
7', 1117W/E h<'i; T-variant level converting means, the above-mentioned level converting means is provided with By changing the conversion correspondence of the level converting means, high-contrast gradation can be obtained from a low-contrast original.

〔Example〕

Hereinafter, the present invention will be described in detail based on Examples.

First Embodiment FIG. 1 shows a block diagram of an embodiment of the present invention. In the illustrated embodiment, prior to scanning for outputting image data, scanning for detecting the appearance frequency of image density (hereinafter referred to as prescanning) is performed.

Here, the control for scanning the original is performed by the CPIII driving a scanning system and an exposure system (not shown). , -37
1 book ``I control is a well-known technology and its explanation will be omitted.

An image signal photoelectrically converted by an imaging section 1 including an imaging device such as a CCD is subjected to multi-value quantization by a ^10 conversion section 2. Here, during the briscan, the switch 6 is set to the adder 7 side under the control of the CPU II.

The frequency of appearance of each density (hereinafter referred to as a density histogram) of the multi-level quantized data is counted by an adder 7 and stored in a histogram memory 8 . The contents of this histogram memory 8 are shown in FIGS. 2 and 5. FIG. 2 is a density histogram of an image with low contrast in a low density area. FIG. 5 is a density histogram of an image with high density and low contrast.

After completing this bliscan, the CPU II refers to the contents of the histogram memory 8 and outputs a conversion table to the conversion table memory IO.

This situation is shown in FIGS. 3 and 6.

That is, as shown in FIGS. 2 and 5, if the lowest density appearing in the manuscript is Dmin+the maximum density is Dmax,
CPIII detects this DIllIn+DIIIaM by referring to the histogram memory 8, and
<D-+o, then D' = O D,. If < D < 0□8, D' = 255/(D-a--Damn) * (D
-Dsa+n) D, , <D, calculate the conversion table based on D' = 255 [Formula 1] (see FIG. 3 or FIG. 6), and write this calculation result into the conversion table memory 10.

Next, the switch 6 is switched to the converter 9 side, and scanning is performed to output an image signal. In this case, ^/D
The multi-level quantized data from the converter 2 is input to the converter 9, which performs level conversion according to the conversion table in the conversion table memory 10, and after which the gradation processing unit 5 performs gradation processing such as dither processing. Output.

As a result, an image with a density histogram as shown in Figure 2 can be converted using the conversion table shown in Figure 3, and an image with a density histogram as shown in Figure 5 can be converted using the conversion table shown in Figure 5.
The level is converted using the conversion table shown in the figure, so
Both are output as if they had a high-contrast density histogram as shown in FIG. 4 or FIG. 7. In other words, it is possible to always obtain a high-contrast image from a low-contrast original.

Paper two! and 1 Onimawari In the second embodiment, CPU II
is the DI for the concentrations that appear more than a certain number (N)
IIaK and Dml. The conversion table is output to the conversion table memory 10 using equation 1 as in the first embodiment. This situation is shown in FIGS. 8 and 9.

Thereafter, similarly to the first embodiment, the conversion table memory 10
The level conversion is performed according to the conversion table in the image data, and the gradation processing unit 5 performs gradation processing such as dither processing. In this embodiment, in order to prevent the level conversion described above from malfunctioning due to dust or scratches on the original, densities whose appearance frequency is less than a constant (N) are ignored. . Here, the constant number (N) is determined appropriately depending on the reading resolution of the imaging unit 1 (for example, the amount of data per square meter) and the minimum size that you want to read as the area with the highest (or lowest) density. A large amount will be used. This embodiment is effective because the level conversion is not affected by dust, scratches, etc., especially when reading an enlarged projected image of microfilm or the like.

Third Embodiment In the third embodiment, when a density histogram is generated by Briscan as in the first embodiment, the frequency of appearance is counted for all the reading areas 13, as shown in Fig. 1O. Instead, a photometric area 12 is provided in the center, and the frequency of appearance is counted only within this area.

This is achieved by regulating the driving part of a sensor such as a CCD included in the imaging section 1 during pre-scanning by controlling l:Pt1H.

The CPU II refers to the density histogram generated for the photometric area 12 in the center and determines the maximum density DIIIaK.
+minimum density D-to (or, as shown in the second embodiment, 0.□ for the density that appears a certain number or more
and D-to), the conversion table is output to the conversion table memory 10 using Equation 1, similarly to the first embodiment. From then on, similarly to the first embodiment, the conversion table memory l
Level conversion is performed according to the conversion table in O, and gradation processing such as dither processing is performed by the gradation processing section 5.

In this embodiment, as shown in FIG. 1O, when there is no original in all of the read image (14 in FIG. 10 is the original), the portion 15 where there is no original in the read image It is possible to avoid malfunction of level conversion.

〔Effect of the invention〕

As explained above, according to the present invention, the conversion correspondence of the level converting means is changed according to the appearance frequency of each density level of the original, so that a low-contrast original can be changed to a high-contrast original without impairing the gradation of the original. It becomes possible to obtain gradations of .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
Fig. 7 is a diagram showing the operation of the first embodiment of the present invention, Figs. 8 and 9 are diagrams showing the operation of the second embodiment of the invention, and Fig. 1O is a diagram showing the operation of the second embodiment of the present invention. A diagram showing the third embodiment and FIG. 11 are diagrams showing the prior art. DESCRIPTION OF SYMBOLS 1... Imaging unit, 2...^/D conversion unit, 5... Gradation processing unit, 6... Switch 1 7... Adder, 8... Histogram memory, 9... Converter, 10... Conversion table memory, 11... CPt1. 1st intervention 1L temperature diagram Figure 11

Claims (1)

[Scope of Claims] 1) In an image reading device that scans and exposes an original image and performs photoelectric conversion using an image sensor, the image reading device comprises: quantization means that converts an image density signal obtained by scanning into a plurality of density level values; a detection means for detecting a range of quantized density levels obtained from the quantization means; a level conversion means for inputting the output of the quantization means, converting it into a predetermined correspondence relationship and outputting it; An image reading apparatus comprising: a control means for setting a conversion correspondence in the level conversion means according to a range of quantized density levels. 2) An image reading device that scans and exposes a document image and photoelectrically converts it using an image sensor, comprising: a quantization unit that converts an image density signal obtained by scanning into a plurality of density level values; adding means for calculating the appearance frequency for each quantization concentration level; level conversion means for inputting the output of the quantization means, converting it into a predetermined correspondence relationship and outputting it; and quantization concentration level obtained from the addition means. an image reading device comprising: a control means for setting a conversion correspondence in the level conversion means according to a frequency of appearance of each image reading apparatus.