JPH03120958A - Picture reader - Google Patents

Abstract

PURPOSE:To obtain a gradation with a high contrast from an original with a low contrast without losing the gradation of the original by expanding the range of the density level appearing frequently for a prescribed number of times so as to attain all prescribed density levels. CONSTITUTION:An adder as a frequency of appearance detection means 7 detects the frequency of appearance (density histogram) of each density level and a gradation processing section as an expansion means 9 applies gradation processing so as to take all prescribed density levels based on a dither pattern stored in a dither pattern memory 10. That is, the density of an original picture is quantized by a quantization means 2, the frequency of appearance of each quantized density level by the quantization means 2 is detected by the frequency of appearance detection means 7 and the range of the density level appearing more than the prescribed frequency of appearance with respect to the frequency of appearance detected by the frequency of appearance detection means 7 is expanded by the expansion means 9 so as to obtain all prescribed density levels. Thus, the picture with high a contrast is obtained from an original with a low contrast.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image reading device, and particularly to an image reading device that reads gradation images such as photographs.

[Prior Art] As a conventional image reading device having a solid-state image sensor such as a CCO, the one shown in FIG. 14 is known.

For example, this may be reflected light from a document placed on a document table by the imaging unit 1 having a solid-state image sensor such as a CCD, or
Alternatively, the projection light of the microfilm is scanned, photoelectrically converted, and multivalued quantized by the A/D converter 2 as quantization means.

The multi-value quantized data obtained by multi-value quantization is converted by the gradation processing unit 5 into 110 binary data that can reproduce a gradation image using a dither method or the like. That is, the first
From the divisor memory 20 that stores dot patterns as shown in FIG. 5, a dot pattern having a dot density proportional to the density data of the image as shown in FIG.
They are read out and output in sequence.

[Problems to be Solved by the Invention] However, even for originals with low contrast in low density areas as shown in FIG. However, since the gradation is faithfully reproduced, the contrast of the reproduced image is also low, similar to that of the original.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image reading device that can solve the above-mentioned problems and obtain a high-contrast image from a low-contrast original.

[Means for Solving the Problems] In order to achieve such an object, the present invention provides a quantization means for quantizing the density of a document image, and a method for calculating the appearance frequency of each density level quantized by the quantization means. Appearance frequency detection means for detecting the occurrence frequency, and extension means for extending the range of concentration levels that appear with a predetermined frequency or more among the appearance frequencies detected by the appearance frequency detection means so as to take a predetermined total concentration level. Features.

[Function] In the present invention, the density of the original image is quantized by the quantization means, the appearance frequency of each density level quantized by the quantization means is detected by the appearance frequency detection means, and the appearance frequency of each density level quantized by the quantization means is detected by the appearance frequency detection means. The range of density levels that appear at a predetermined degree of opening or more among the occurrence frequencies is extended by the extension means so as to have a predetermined total density level.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention.

In the figure, 1.2 indicates the same part as in FIG. 14.

Reference numeral 7 denotes an adder as appearance frequency detection means, which detects the appearance frequency of each density level (hereinafter referred to as density histogram). A histogram memory 8 stores the density histogram obtained by the adder 7.

11 is a CPU that determines a dither pattern based on the histogram stored in the histogram memory 8; IO is a dither pattern memory that stores the determined dither pattern. Reference numeral 9 denotes a gradation processing section as an expansion means, which performs gradation processing so as to obtain all predetermined density levels based on the dither pattern stored in the dither pattern memory 10. Reference numeral 6 denotes a changeover switch that switches the data from the A/D converter 2 to the adder 7 side during blisscanning and to the gradation processing unit 9 side during scanning.

The image reading device of this embodiment is configured to perform scanning (hereinafter referred to as blisscan) for detecting the appearance frequency of each density level prior to scanning for outputting image data.

(1) A control procedure by the CPU 11 when reproducing an image with low contrast in a low density area as shown in FIG. 17 will be explained.

This is the case for a dither pattern with 4×4=16 gradations.

The density histogram obtained by Briscan is
This density histogram is stored in the histogram memory 8 as shown in the figure.

After the blisscan is completed, the contents of the histogram memory 8 are referred to and the dither pattern shown in FIG. 3 is stored in the dither pattern memory IO.

That is, with reference to the histogram memory 8, the minimum density Dmin and maximum density DllIa× of the original are detected;
The density data is converted into the number of dots based on Table 1, and the dither pattern is written into the dither pattern memory 1o.

(Margin below) Table 1 Next, the switch 6 is switched from the adder 7 side to the converter 9 side, and scanning for outputting an image signal is started.

^/The multi-value quantized data from the D converter 2 is sent to the gradation processor 9.
The image is dithered according to the dither pattern input to the dither pattern memory 10 and stored in the dither pattern memory 10, and the number of dots is converted to have a density histogram as shown in FIG. 4, resulting in an image as shown in FIG. Output.

(2) A control procedure by the CPU 1.1 when reproducing an image with low contrast in a high density area as shown in FIG. 18 will be explained.

In this case, compared to the case (1) above, the dither pattern stored in the dither pattern memory 10 is different. That is, in contrast to the case (1) shown in FIG. 3, the structure shown in FIG. 6 was adopted. Since this is done, the effect is essentially the same as that in case (1) above, and in this case as well, an image as shown in FIG. 8 is output.

In this embodiment, by referring to the histogram memory 8, the dither pattern memory lO is
However, CPIJII allows you to rewrite the input/output relationship using γ (not shown).
A γ conversion unit 21 having a conversion table memory is provided between the switch 6 and the gradation processing unit 9 as shown in FIG. The input/output relationship may be rewritten as shown in FIG.

Further, the tone processing section 9 is not limited to the dither method, and may use other tone expression methods such as the well-known error diffusion method.

11. Comparing this embodiment with the first embodiment, the dither pattern stored in the dither pattern memory 10 is different.

That is, in the first embodiment, the highest density of the original is set to the highest density Dmax, which corresponds to 18 dots, and the lowest density is set to the lowest density Dmin, which corresponds to 0 dots. As shown in Figure 12, a predetermined number of times (
N) The highest concentration among the concentrations generated above is the highest concentration Dm
The ax corresponds to 16 dots, and the lowest density among the densities that occur a predetermined number of times (N) or more is the minimum density Dmin, which corresponds to 0 dots. Here, an appropriate value for N is used depending on the reading resolution of the imaging unit 1, for example, the amount of data per square ma, and the minimum size desired to be read as the highest (or lowest) density area. Since this is done, the effects of this embodiment are the same as those of the first embodiment. However, when reading a document, especially an enlarged projected image of a microfilm, etc., there is an advantage that it is possible to remove the effects of level conversion such as dust and scratches.

11. In comparison with the first embodiment, this embodiment differs in the area on the document where the appearance frequency of each density level is detected. That is, in the first embodiment, the entire area was used in the document shown in FIG. 13, but in this embodiment, the photometry area 12 was used in the center. Since this is done, the effects of this embodiment are the same as those of the first embodiment. However, as shown in FIG. 13, there is an advantage that appropriate gradation conversion can be performed even when the document 14 is not present in the entire area of the read image.

[Effects of the Invention] As explained above, according to the present invention, with the above configuration, high contrast gradation can be obtained from a low contrast original without impairing the gradation of the original. There is an effect.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the first embodiment of the present invention, FIG. 2 is a density histogram showing the appearance frequency of each density level of the image shown in FIG. 17, and FIG. 3 is a dither diagram for the density histogram shown in FIG. A diagram showing an example of a pattern, FIG. 4 is a density histogram showing the appearance frequency of each density level of an image obtained by conversion using the dither pattern shown in FIG. 3, and FIG. 5 is a density histogram showing each density level of the image shown in FIG. 18. A density histogram showing the frequency of level appearance; FIG. 6 is a diagram showing an example of a dither pattern for the density histogram shown in FIG. 5; FIG. A density histogram showing the degree of appearance and opening of density levels, Fig. 8 is a graph obtained by converting the image shown in Fig. 17 with the dither pattern shown in Fig. 3, and the image shown in Fig. 18 with the dither pattern shown in Fig. 6. FIG. 9 is a block diagram showing an image reading device having the γ converter 21; FIG. 10 is a diagram showing an example of the human output relationship of the γ converter 21; FIG. Maximum concentration Dmax in 2 examples
FIG. 12 is a diagram showing a dither pattern in the second embodiment of the present invention, and FIG. 13 is a diagram showing the frequency of appearance of each density level in the third embodiment of the present invention. 14 is a block diagram showing a conventional image reading device; FIG. 15 is a diagram showing an example of a dot pattern; FIG. 16 is a diagram showing an example of a conventional dither pattern; FIG. 17 is a diagram showing an example of an image with low contrast in a low density area, and FIG. 18 is a diagram showing an example of an image with low contrast in a high density area. DESCRIPTION OF SYMBOLS 1... Imaging unit, 2...^10 conversion unit, 6... Changeover switch, 7... Adder, 8... Histogram memory, 9... Gradation processing unit, 10... Dither pattern memory, 11...cpu. The slope of the construction is 1. Figure D Dot rotation diagram Artwork J quality diagram Figure 1 O Figure 9! ! J Miga 1 LOL 1 Figure π 12 Figure 14 Figure 16 Nail Figure 18

Claims (1)

[Scope of Claims] 1) Quantization means for quantizing the density of a document image, appearance frequency detection means for detecting the appearance frequency of each density level quantized by the quantization means, and the appearance frequency detection means 1. An image reading device comprising: an expanding means for expanding a range of density levels that appear with a predetermined frequency or more out of frequencies of appearance detected by the above method so as to take a predetermined total density level.