JPS646587B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an image reduction method for reproducing a reduced image by processing a digital image signal read by scanning and sampling an original image pixel by pixel. Conventionally, this type of image reduction method, as shown in Figure 1, involves regularly removing pixels indicated by diagonal lines in the figure from the sampled pixel array, and reducing the pixel pitch during recording by that amount. A so-called regular sampling method has been proposed. However, with such conventional image reduction methods,
If a periodic pattern is included in the original image, moiré (image unevenness) will occur in the reproduced image, and there is a high risk that thin line portions will be missing. The present invention has been made with these points in mind, and it is an object of the present invention to provide an image reduction method that can reproduce high-quality images without causing moiré or missing thin lines. The image reduction method according to the present invention, when reducing an image by reducing the number of pixels in the main scanning direction, does not only extract specific sampling pixels as in the conventional method, but also changes the pixel pitch. At the new position, resampling is performed using the original sampling pixels in the vicinity. Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings. As shown in FIG. 1, in the image reduction method according to the present invention, a pixel array ORG obtained by scanning and sampling an original image is converted to a pixel array ORG with a pixel pitch different from the pitch _p of each sampling pixel.
Convert the pixel string CNV with P _c (p _c > p _p ) using the following calculation process, and reproduce the reduced image with the pitch at the time of recording being the same as the output pitch in the case of the original pixel string ORG. It is something that allows you to do this. Now, in order to obtain the converted pixel sequence CNV,
Focusing on the converted pixel P _c (l+1),
In the present invention, the position of the converted pixel P _c (l+1) is
The corresponding original sampling pixel sequence ORG
Two adjacent pixels P _O (k) on the left and right in
It is determined in association with each position of P _p (k+1), P _o (k+2), and P _p (k+3) (k represents the number of each sampling pixel). That is, the intervals between the converted pixel of interest P _c (l+1) and the original sampling pixels P _O (k+1) and P _p (k+2) are α _l+1 and β _l+1 (α _l+1 +β _{l+ 1} = P _p ), each of the four pixels P _p (k+n) (n=0 to 3) in the original sampling pixel array ORG when the position of the converted pixel P _c (l+1) is 0. The positions are −(p _p +α _l+1 ), −α _l+1 , β _l+1 , p
_p +
It is expressed as β _l+1 . The correction functions Sn for the positions of each of the four pixels P _p (k+n) whose parameters have been converted in this way are given by the following equations. S ₀ = S {-(p _p + α _l+1 )} S ₁ = S (-α _l+1 ) S ₂ = S (β _l+1 ) S ₃ = S (p _p + β _l+1 ) …( 1) Therefore, using each of these values S ₀ to _{S 3} as a weighting coefficient, the four pixels P _p are calculated according to the following formula.
If the sum of each density level Q _p (k+n) of (k+n) is calculated, the resampled converted pixel P _c (l
+1) concentration level Q _c (l+1) is determined. Q _c (l+1)= ₃ 〓 ⁱ⁼⁰ Si·Q _p (k+i) (2) Note that the function S(x) in this case is usually a Sinc function as shown in FIG. In this way, in the image reduction method according to the present invention,
The image is reduced by performing certain arithmetic processing that takes into account the weighting coefficients of the two adjacent pixel positions on the left and right sides of the original sampling pixel column in response to the converted pixel position to be resampled. Therefore, it is possible to reproduce a high-quality reduced image without causing moiré or missing thin lines as in the conventional case. FIG. 3 shows an example of a configuration for concretely implementing the image reduction method according to the present invention described above.
4-bit shift register that sequentially reads DATA
SR and a quinary counter CNT1 which is cleared in response to the synchronization signal SYNC and which counts the clock signal CLK and generates the input pixel position signal γ.
, its counter output γ and the shift register
The parallel outputs s ₁ to _{s 4} from each bit of the SR are sent as addresses, and in response, the contents of the weighted calculation results according to the above formula (2) are recalled in advance. , a shift register TSR with a toggle function that temporarily collectively stores the output O of the ROM and then sends the reduced image data O' to an external blotter;
The clock signal CLK and synchronization signal are used to read and read data from the shift register TSR.
Controller that is executed appropriately depending on SYNC
It is composed of CONT and With this configuration, the reduction ratio is 0.8
The operation for reducing the original image will be described below with reference to a timing chart of various signals shown in FIG. Now, the data signal DATA of each pixel for each line (the number of sampling pixels is 2048 for an A4 size document) sent from the scanner in synchronization with the clock signal CLK is sequentially read into the shift register SR. Each of the 4-bit parallel outputs _s1 to _s4 corresponds to four pixels P(k), P(k+1),
It is sent to the ROM as corresponding to P(k+2) and P(k+3), respectively, and at the same time the synchronization signal SYNC
The quinary counter CNT cleared by starts counting in synchronization with the clock signal CLK, and the count output γ is used as a signal indicating the position of the converted pixel P _c .
Sent to ROM. In this case, when γ=0, it is a case where the converted pixel P c and the sampling pixel P _p overlap, as shown in P _c (l) and P _p ( _k ) in FIG. When = 1, the converted pixel P _c is P _c
At the position (l+1), when γ=2, the converted pixel
P _c is at the position of P _c (l+2), and when γ=3, the converted pixel P _c is at the position of P _c (l+3), respectively.
Further, when γ=4, there is no corresponding conversion pixel R _c , and after counting γ=4, the count CNT resets its contents and repeats the counting from γ=0 to 4 again in sequence. Also, in the table below,
The relationship between the contents of the shift register SR at this time and the position of the converted pixel P _c obtained at that time is shown.

[Table] Next, in accordance with the position signal γ of the converted pixel P _c at that time, the ROM performs the _above -mentioned ( ₂ ) is called, and its output signal O is sent to the next stage shift register TSR together with the valid signal v. At this time, the valid signal v output from the ROM when γ=4 becomes low level "L", and the shift register
The TSR is designed not to read the output signal O of the ROM at that time in order to invalidate it.
In addition, a shift register with toggle function
TSR controls the switching of input and output.
It is executed by the switch command SW according to the synchronization signal SYNC from CONT, and the controller
The data O output from the ROM is sequentially read and shifted in synchronization with the clock signal CLK output from CONT, and the image data signal O' with the number of pixels per line converted to 1638 is sent to the blotter. Image reproduction is performed with a reduction ratio of 0.8. As described above, in the image reduction method according to the present invention,
Based on the image information read by scanning and sampling the document pixel by pixel, resampling is performed at a new pixel position with a changed pixel pitch in the main scanning direction, and the original sampling pixel corresponding to the resampling position is resampled. left in column,
The image is reduced by performing certain arithmetic processing that takes into account the weighting coefficients of each two pixel positions adjacent to the right to determine the density level of the resampled pixel. It has the excellent advantage that high-quality reduced images can always be reproduced regardless of the situation.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the correspondence of each pixel in a sampling pixel string and its converted pixel string, and FIG. 2 is a diagram showing the relational characteristics of the arithmetic processing according to the present invention when focusing on the converted pixel P _c (l+1). 3 is a block diagram showing an example of a configuration for concretely implementing the image reduction method according to the present invention, and FIG. 4 is a timing chart of various signals in the same embodiment. ORG...sampling pixel array, CNV...conversion pixel array, SR...shift register, CNT...quintal counter, TSR...shift register with toggle function,
CONT…Controller.

Claims (1)

[Claims] 1. Based on the image information read pixel by _pixel by scanning and sampling the original image in the main scanning direction at a pixel pitch p _p in the original main scanning direction. Large pixel pitch p _c
The resampled pixel of interest P _c (l+1) to be processed and the original two sampling pixels P _p (k+1) and P _p ( k+2) are respectively α _l+1 and β _l+1 (α _l+1 + β _l+1 =p _p ), there are two on the left and two on the right of the resampled pixel of interest. The correction function Sn for the original four sampling pixels P _p (k+n) (n=0 to 3) is calculated according to the following formula (1), and the calculated correction function Sn is used as a weighting coefficient to calculate the following formula ( 2) An image reduction method that determines the density level Q _c (l+1) of the resampled pixel of interest according to 2). S ₀ = S {-(p _p + α _l+1 )} S ₁ = S (-α _l+1 ) S ₂ = S (β _l+1 ) S ₃ = S (p _p + β _l+1 ) …( 1) Q _c (l+1)= ₃ 〓 ⁱ⁼⁰ Si・Q _p (k+i) …(2)