JPH03292063A - Color picture reading method - Google Patents

Abstract

PURPOSE:To balance the resolution of three colors by taking a red color as a reference, not implementing weighing calculation to a red signal, but implementing weighing calculation to a green and a blue signal when the deviation of a read position of each color is corrected by the weighing calculation in the case of reading a color original. CONSTITUTION:A 1st line green signal G1 is read, a one preceding line blue signal B1 is read from a memory section 11 and fed to a green signal weighing circuit 3 and a blue signal weighing circuit 10 respectively and the red and blue signals are subject to 1/3 or 2/3 weighing depending on the distance of each red/green color with respect to the red color signal taken as a reference (1/3 for remote position and 2/3 for close position). Thus, the read position of the green and blue signals is corrected nearly to the read position of the red color and the read position of the three colors is made coincident. Thus, no color slurring takes place in the output picture.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color image reading method used in digital color copying machines and the like.

[Conventional technology]

Generally, in a color image reading device, an image of a document is separated into three components of red, blue, and green to obtain three-color signals.

FIG. 4 shows an example of a general color image reading device.

An original (not shown) placed on platen glass 1 is sequentially irradiated with red, blue, and green exposure lamps 2R, 28, and 2G, and reflected light from the original passes through a plurality of mirrors 3a to 3C and lens 4. and forms an image on a one-dimensional image sensor 5. Exposure lamps 2R, 28, 2G, mirrors 3a to 3
The document scanning unit A, which is composed of 0, etc., is movable in the left-right direction by a scanning motor (not shown) in the range from the position shown by the solid line to the position shown by the dashed-dotted line in the figure. The image sensor 5 reads the image of the original in the sub-scanning direction, that is, in the direction of arrow B, while reading one line of the image in the main scanning direction of the original, that is, in the direction perpendicular to arrow B.

When performing this reading, it is originally desirable to sequentially expose the same part of the document in the three colors of green, red, and blue, and then advance the document scanning section A by one line and perform the next exposure. If this is performed discontinuously, the scanning mechanism and control system become complicated, and the document cannot be moved smoothly to the document scanning section.

Therefore, while continuously moving the document scanning 1 mA in the direction of arrow B, that is, while sub-scanning, the image is green at time point i++ t2+ tI as shown in FIG. 5(a).

Sequential exposure with red and blue is performed. in this case,
The exposure position for each color is slightly shifted in the scanning direction of the document, so as shown in FIG. 6), the exposure position is green.

The red and blue color signals G, , R, , B are different from each other. For this reason, if these color signals are synchronized, color shift will occur.

Therefore, in conventional color image reading devices, when reading documents, approximately Green, red, and blue color signals G, R, and B are obtained at the same location. That is, while continuously moving the original scanning unit A as shown by the solid line in FIG. 6(a),
t2v t3+ t4+ tS+t6 green, red, blue,
Exposure is performed in the order of green, red, and blue, and Gl is detected from the image sensor 5 as shown in FIG.

Color signals of R,, Bl, Gl, R9, B are obtained. Then, when the exposure for 2 lines is completed, green, red 7
Blue output signal Gout, Rout, BOUT, G
o, Jt = 02.

As a result, each color signal can be obtained in the same manner as when reading is performed stepwise line by line, as shown by the broken line in FIG. 2(a). Note that the reason why the edges are weighted as a reference is because, as mentioned earlier, out of the 23 colors, green has the highest visibility for humans and has the greatest impact on vision.

[Problem to be solved by the invention]

However, when the red and blue color signals are obtained by weighting with green as a reference in this way, the following disadvantages occur.

First, when a color signal is determined by weighting, the resolution in the sub-scanning direction of red and blue determined by calculation deteriorates compared to that of green, which serves as a reference.

Further, due to chromatic aberration in the lens 5, the focal lengths for each color are different as shown in the graph of FIG. 7, and the focal characteristics of green and blue are similar, but the focal characteristics of red are significantly different. The horizontal axis of the graph is the depth of focus, and the vertical axis is the MTF (
modulation transfer function> characteristics. 9. The depth of focus on the horizontal axis is set to 0 when the imaging plane has the same MTF characteristics for green and blue.
The direction closer to the lens is one direction, and the direction closer to the lens is the sub direction. In addition, the MTF characteristic on the vertical axis is 5 Rps (li
This shows the response when a sine wave (ne-pairs) is input. In this case, if the optical system is designed to focus on green and blue, the characteristics for two of the three colors can be satisfied, so this is usually the design. Therefore, a focus shift occurs with respect to red, resulting in a decrease in resolution. In addition, if you use a lens with excellent chromatic aberration characteristics,
Although it is possible to prevent a decrease in resolution due to defocus, in this case there is a problem that the lens becomes very expensive and large.

The resolution of red is considerably degraded compared to the other two colors due to two reasons: the above-mentioned weighting calculation based on green and focus adjustment based on green and blue. When the resolution of red is reduced in this way, not only the sharpness of the image is reduced, but also unnecessary colors are generated as described below. That is, when reading a black and white ladder pattern as shown in Figure 8(a), ideally it would be desirable to obtain a rectangular waveform signal as shown in Figure 8(b) for each color number 43, but in reality Since there is a limit to the resolution of the optical system, the waveform becomes dull as shown in FIG. Moreover, since the resolution of red is low, the amplitude of the red signal shown by the broken line is smaller than the amplitude of the green signal and the blue signal shown by the solid line.

After each color signal is read by the image sensor 5, it is binarized using a predetermined threshold value. For example, when the color signal is binarized using the threshold value thl shown in FIG. 8(C), the lowest level of the green signal and the blue signal is The lowest level of the red signal does not reach thl, whereas it becomes below the threshold th1. Therefore, each color signal Sc of green, red, and blue.

The waveforms of Sl and SB are as shown in (d) to (f) of the figure.

For this reason, as shown in FIG. 3(g), a portion that should originally be black is read as red.

In addition, if a higher threshold value th2 is used as shown in (C) of the same figure, the waveforms of each color signal Sc, Sa+ sB will become as shown in (B) to (D) of the same figure, and the center part of black will be correctly black. However, as shown in Figure 1!! (g), both sides of black are still read as red.

That is, since the resolution of red in the conventional color image reading device is lower than that of other colors, there is a problem that an image different from the original is read.

In addition, positional deviation in the main scanning direction occurs not only when color separation is performed by blinking each color light source described above, but also when color separation is performed by a color image sensor.

That is, in a color image sensor, as shown in FIG. 9, a plurality of light receiving elements S, S, .

... are arranged linearly in the main scanning direction indicated by arrow C, and each light receiving element S Ill 311411... is arranged linearly in the main scanning direction as shown by arrow C. Each light receiving element S Ill 311411... A, S key 11.5llh+ sG. . Ill
5Rfh+l]+SR[h,),... Therefore, a certain distance l exists between each color sensor. Therefore, even if the document is read while being held still with respect to the color image sensor, a reading error in the main scanning direction will occur in principle. Therefore, the reading output is corrected by weighting calculation as described above, but in this case, the resolution also decreases.

The same applies to focal shifts caused by chromatic aberration of lenses.

Therefore, an object of the present invention is to increase the resolution of red so that the image of the original can be read faithfully.

[Means to solve the problem]

In order to achieve the above object, the color image reading method of the present invention uses the red reading position as a reference in a color image reading device in which reading positions of the edges, red, and blue of the same image are slightly different in the scanning direction. , by performing a weighting operation on the plurality of reading outputs of each of the green and blue colors obtained at a plurality of adjacent locations, the reading position of each of the green and blue colors is approximately corrected to the reading position of the red color. It is characterized by

The weight of the weighting calculation may be a value inversely proportional to the distance from the red reading position to the green and blue reading positions.

〔Example〕

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, features of the present invention will be specifically described based on examples with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a color image reading device to which the present invention is applied. Note that the same reference numerals are given to the members corresponding to those of the conventional example shown in FIG. 4.

In this embodiment, as in the conventional example, the exposure lamps 2R, 28, 2G and the mirrors 3a to 3c are used for original printing.
0, while continuously moving to the document scanning unit consisting of etc.
Each color signal is obtained from the image sensor 5 by sequentially and cyclically exposing the document. However, in this embodiment, exposure is performed in the order of red, blue, and green.

These time-divided color signals are stored in the first and second RAMs, which are independently written and read out from RAM.
A memory 6.7 is supplied. First and second memory 6.7
are provided with memory sections 6R, 6B, 6G, 7R, 7B, and 7G that sequentially store red, blue, and green color signals, respectively.

The outputs of the green signal memory units 6G and 7G are combined and then directly supplied to one input terminal of the weighting circuit 8, and the other input terminal of the weighting circuit 8 is provided with a memory that delays one line. 9. Similarly, the green output of the memory section 687 for the blue signal is supplied to the weighting circuit 1o with a time difference of one line added by the memory section 11.

Further, the outputs of the memory sections 6R and 7H for red signals are combined and then directly output.

Next, regarding the operation of the above-mentioned color image reading device,
This will be explained with reference to FIGS. 2(a) and 2(b).

First, when reading the first line of the original image, the first memory 6 is set to the write mode, and the second memory 7 is set to the read mode. In this state, the exposure lamps 2R, 2
8 and 2G are lit in red 1, blue, and green in order, and the original is exposed. Therefore, color signals corresponding to each color are sequentially obtained from the image sensor 5, and each color signal R,,B,...
G is the memory section 6R, 6B, 6G of the first memory 6
are written sequentially.

When reading the second line, the first memory 6 is in the read mode and the second memory 7 is in the write mode. Then, this time, each color signal R2, B of the second line
2+ Gi is the memory part 7R, 7B of the second memory 7,
They are sequentially written to 7G. Also, at the same time, each color signal R,, B, of the first line was written in the memory sections 6R, 6B, 6G of the first memory 6.

G1 is read out at the same time.

Then, when reading the third line, the first memory 6 is set to the write mode again, the second memory 7 is set to the read mode, and each color signal Rs, B3 of the third line is read.
．． While G 3 is sequentially written into the first memory 6,
The color signals R2+B2+G2 of the second line are simultaneously read out from the second memory 7. At this time, the green signal G of one line before from the memory section 9, that is, the first line,
At the same time, the blue signal B of one line before is read out from the memory section 11. At this point, each point P l+ P 2+ P 3+ P4 in FIG. The output at P, is G s, G as shown in Fig. 2(a).
+, R2, B 2. It becomes B+.

The outputs of the points p, , p2 are supplied to the green signal weighting circuit 3, where the weighting calculation of 3 is performed, and the green output signal G is obtained. TIT is obtained.

Similarly, the outputs of points P, , Pa are supplied to the blue signal weighting circuit 10, where 3 weighting calculations are performed to obtain one blue output signal Bflt.

In addition, the output R2 of point P is the red output signal R8 as it is.
It becomes LIT. That is, Rout=R2.

Output signals G of each color obtained in this way. uT+R
Out and Bout are supplied to a color image output device using an electrophotographic method or a thermal transfer method to form a color image.

At this time, as schematically shown in Figure 2 (b), for the green and blue signals, the farther one is weighted by 1/3 and the closer one is weighted by 273, depending on the distance from the red reading position. Therefore, the reading positions of each color of green and blue are approximately corrected to the reading position of red, and the reading positions of the three colors coincide. Therefore, no color shift or the like occurs in the output image.

In addition, in the above-mentioned embodiment, each color exposure lamp 2R
. Color image sensor 1 having a structure as shown in
The present invention can also be applied to a color image reading device that performs color separation according to 2. Note that the same reference numerals are given to the members corresponding to those of the embodiment shown in FIG. In this case, instead of the first memory 6 consisting of memory sections 6G, 68.6G and the second memory 7 consisting of memory sections 7R, 7B, 7G shown in FIG. 1, latches 13R, 13B,
First latch part 13 consisting of 13G, latches 14R, 14
A second latch section 14 consisting of B and 14G is used. Furthermore, in place of the memory section 9.11, a latch section 15.16 that delays by one pixel is used. Then, instead of performing weighting calculation between lines, weighting calculation may be performed between pixels adjacent in the main scanning direction using red as a reference.

〔Effect of the invention〕

As described above, according to the present invention, red is used as the reference when correcting the deviation of the reading position for each color by weighting calculation when reading a color original. That is, the weighting calculation is not performed on the red signal, but the weighting calculation is performed on the green signal and the blue signal. As a result, the resolution of red, which originally tends to deteriorate more than the other two colors, is prevented from further deteriorating, and the resolution of the three colors can be balanced. Therefore, for example, even if a black and white ladder pattern is read, 3
Both colors are binarized with the same convergence, which can prevent the generation of unnecessary colors.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a color image reading device to which the present invention is applied, FIGS. 2(a) and (b) are diagrams for explaining the operation of the same color image reading device, and FIG.
The figures are block diagrams showing other embodiments of the present invention, FIG. 4 is a schematic sectional view showing an example of a general color image reading device, and No. 51! I is a diagram to explain the deviation of the reading position when scanning the original, Figures 6 (a) and (b) are diagrams to explain the reading of a color original by time division, and Figure 7 is green and red. , an explanatory diagram showing the difference in lens focal length for each color of blue, Figures 8(a) to (2) are diagrams to explain the occurrence of unnecessary colors when reading a black and white ladder pattern, and Figure 9 is an explanatory diagram showing the difference in lens focal length for each color of blue. FIG. 3 is a diagram illustrating a shift in a reading position when color separation is performed by a color image sensor. 1 Nibraten glass 2, 2G, 2R, 2B: Exposure lamps 3a to 3C: Mirror 4: Lens 5: Image sensor 6: First memory 7: Second memory 8, 10: Weighting circuit 9.11
: Memory section 12: Color image sensor 13: First latch section 14; Second latch section 15.16: Latch section A: Original scanning section D = Original

Claims (1)

[Scope of Claims] 1. In a color image reading device in which reading positions of red, blue, and green for the same image are slightly different in the scanning direction, reading positions of red, blue, and green are obtained at a plurality of adjacent positions with respect to the reading position of red as a reference. The color image is characterized in that the reading position of each of the green and blue colors is approximately corrected to the reading position of the red color by performing a weighting calculation on the plurality of reading outputs of each of the green and blue colors. How to read. 2. The color image reading method according to claim 1, wherein the weight of the weighting calculation is inversely proportional to the distance from the red reading position to the green and blue reading positions.