JPH0636552B2 - Image quality control device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an image quality control apparatus for a multi-tone image.

[Prior art]

2. Description of the Related Art An image reading apparatus having a function of detecting the density of a read image and controlling the density of an output image in accordance with the detected density value has been devised in an apparatus for reading and outputting a multi-tone image.

However, if the document to be read is a document having a completely different density distribution, such as a mixed document of characters and photographs, the density output will be inappropriate.

〔Purpose〕

The present invention has been made in view of the above points, and provides an image quality control device capable of performing appropriate density correction on a plurality of independently designated image regions according to the attributes of the image regions. The purpose is to provide.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 2A and 2B are a side view and a plan view of the image reading apparatus according to the present embodiment, respectively.

1 is a document to be read, 2 is a transparent document table, 3-1 and 3-2
Is a lamp for illuminating the original, 4-1, 4-2 and 4-3 are mirrors, 5 is a lens, and 6 is a CCD.

The image of the document 1 illuminated by the lamps 3-1 and 3-2 is formed on the CCD 6 through the mirrors 4-1, 4-2, 4-3 and the lens 5.

On the document surface, electric scanning (hereinafter, main scanning, X in the figure) in the CCD is performed, and at the same time, the lamps 3-1, 3-2, mirrors 4-1, 4-2, 4-3 mechanically scan (hereinafter, Sub-scan,
In the figure, Y) is performed to scan the document.

FIG. 3 shows an image reading procedure in this embodiment.
First, step 18 is pre-scanning, and scanning is performed once before the main scanning for outputting an image, and the characteristic parameters of the document are fetched.

Step 19 creates a density conversion table based on the characteristic parameters fetched by step 18.

Next, in accordance with the density conversion table created in step 19, main scanning is performed in step 20 to read the original and simultaneously output the image.

FIG. 4 describes the characteristic parameters of the original document in this embodiment. If there is a document as shown in Figure 2 (a) 1,
An output after A / D conversion and a characteristic parameter when white is 0 and black is 255 for one main scanning line will be shown.

AV is a predetermined main scanning position AP. As opposed to
It is the average density value at 8 points from AP-3 to AP + 4. WP and BP are predetermined main scanning sections [P
S, PE], the maximum white level and the maximum black level are shown.

That is, the main scanning position i (= 0, 1, 2, 3, ---
The output after the A / D conversion of the CCD in ---) is d (i)
Then, the following equation is established.

In this embodiment, the AV is used to know the gradation information of the original, and the AP may be designated in a portion such as a photo original where the gradation information is considered important.

Further, WP and BP are used to know the maximum black level and the maximum white level of a document, and SP, when the density information of a character part and a background part is considered to be important, such as a character document.
It is sufficient to specify EP.

Further, the values of WP, BP and AV detected for each main scanning line are counted only in the necessary sub-scanning section, and a histogram is formed as shown in FIGS. 5 (a), (b) and (c). And is used to calculate the density conversion table.

FIG. 1 is a block diagram showing the electrical configuration of this embodiment.

6 is the above-mentioned CCD, 7 is an inverting amplifier (hereinafter, amplifier), 8
Is an A / D converter (hereinafter A, D, C), 9 is a density conversion R
AM (hereinafter referred to as conversion RAM), 10 is a white peak / black peak detector (hereinafter referred to as WP / BP detector), 11 is a section average value detector (hereinafter referred to as AV detector), and 12 is MPU, 13, 14, 1
5 is a selector, 16 is an output side interface 17 is a latch.

The image signal read by the CCD 6 is inverted and amplified by the amplifier 7, and then quantized to 8 bits by A, D and C 8,
It is sent to the selector 13.

First, in the pre-scan, the MPU 12 preliminarily follows the operator's instruction and causes the WP / BP detector to detect peak detection sections PS, P.
E is designated, and the average value detection point AP is designated in the AV detector 11. Further, by switching the selector 13 to the lower side in the figure, the data from A, D and C8 are sent to the WP / BP detector 11, and the values of the characteristic parameters WP, BP and AV are set for each main scanning line. It is calculated and sent to the MPU 12.

The MPU 12 sends the characteristic parameters WP, BP,
The AV value is counted only in the required sub-scanning section, and the histogram shown in FIG. 5 is created. Also, depending on the case,
The values of PS, PE, and AP are switched in the middle of sub-scanning, and a histogram of the characteristic parameters of the non-rectangular area or a plurality of areas is created.

After the main scanning is completed, the selectors 14 and 15 are switched to the lower side, and the conversion RAM 9 is switched to the MPU 12 side. Further, a density conversion table is created from the obtained histograms of WP, BP, and AV and written in the RAM 9.

The conversion RAM 9 stores the data before density conversion in the lower address 8
Data 8 after density conversion for bits (A _{0 to} A ₇ ).
Bits (D _{0 to} D ₇ ) are written correspondingly, but since the upper address 3 bits (A _{8 to} A ₁₀ ) can be changed by the MPU 12 via the latch 17, a maximum of eight types of conversion can be performed for one data. The table can be switched.

After the density conversion table is written in the conversion RAM, MP
U12 switches all the selectors 13, 14 and 15 to the upper side, and then shifts to the main scanning operation.

At the time of main scanning, the MPU 12 selects one of the eight types of density conversion tables written in the conversion RAM 9 and reads it while switching to the most appropriate table.

FIG. 6 shows a specific shape of the histogram of WP, BP, and AV and the shape of the density conversion table.

For example, in the case of a document consisting of four parts as shown in FIG. 6 (a), the operator inputs the area into the apparatus in advance. Therefore, W in the character area (I) (II)
Examples of histograms of P and BP are shown in (b) and (d). At this time, if the density conversion tables corresponding to the respective areas are selected as shown in (c) and (e), when the main scanning of each area is performed, the character portion is clearly read and output with respect to the background portion. can do.

In addition, (f) and (h) show examples of histograms of AV in the photo areas (III) and (IV). At this time, for example, for the region (III) that is entirely bright, consider density conversion that makes it dark as shown in (g), and conversely, for the region IV that is entirely dark, Consider a density conversion that brightens the image.

These four types of density conversion tables (c), (e), (g), and (i) are respectively written in the conversion RAM, and in the main scan, the MPU is configured so that the density correction is performed in the corresponding areas. RAM during main scanning and sub scanning
Switch the _A 8 _{~A 10} of 9.

As described above, in the embodiment of the present invention, appropriate density output is performed even for a mixed original of characters, photographs, etc., or an original consisting of portions having completely different density distributions such as a laminated original. be able to.

[Effect] As described above, according to the present invention, an attribute indicating an image type is given to each of the first and second image areas according to the density detected by the density detecting means, and the attribute is determined according to the attribute. By independently performing the density correction in the first and second image areas according to the density correction condition, it is possible to appropriately adjust the density of a plurality of independently specified image areas according to the attributes of the image areas. Corrections can be made.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration, FIG. 2 is a side view and a plan view of this embodiment, FIG. 3 is a diagram showing a procedure for image reading, and FIG. 4 is an image signal in one main scanning line. And FIG. 5 is a diagram showing each characteristic parameter, FIG. 5 is a diagram showing an example of a histogram of each characteristic parameter, and FIG. 6 is a diagram showing a relationship between an image region and a histogram density conversion table.

Claims (1)

[Claims] 1. Input means for inputting an image signal, area designating means for designating an area on an image represented by the image signal input by the input means, and different ones designated by the area designating means. A detection unit that independently detects the densities in the first and second image regions, and an attribute that indicates the image type for each of the first and second image regions according to the densities detected by the detection unit. An image quality control apparatus comprising: a density correction unit that independently performs density correction in the first and second image areas according to a density correction condition according to the attribute.