JPS6339275A - Threshold correcting method - Google Patents

Abstract

PURPOSE:To alter a correction factor according to a relative resolution and to equalize the concentration of a copy by varying the correction factor of the threshold for reading the picture recorded on a film so as to quantize according to the contrast of the picture. CONSTITUTION:When the contrast value of the picture is small and small characters are set for a bit of picture information, one scale constant K is made smaller so as to make the correction factor small. And when the contrast value is large, such as the time large characters are for the bit of picture information, one scale constant K is made larger to make the correction factor large. For example, a threshold set part 4 uses a step value from a concentration set part 1 and the contrast value from a contrast detection part 2 so that it can set and output the threshold by using the correction factor according to the contrast value. Therefore as for both the picture with the large characters group of information and the picture with small characters group of information, the difference of the concentration per the one scale of a copy concentration adjustment scale can be equalized so as to properly adjust the concentration of the copy.

Description

[Detailed Description of the Invention] [Technical Field] (Prior Art) Fig. 5 shows an image density correction section 40 provided in an image reading device.
A lever 41 is provided that is manually moved in response to a copy density correction scale that changes step by step for each scale.By moving this lever 41, a threshold value for quantizing the read output can be set. to correct. Conventionally, the correction factor for correcting the threshold value is correction factor = constant (K) x scale amount (
N), and by setting K to a constant value, the correction factor has linearity, and both large and small characters are corrected with the same correction factor, and the copy density is manually adjusted.

However, if the relative resolution of characters (resolution per character) is low, the copy density adjustment will be coarse and it will not be possible to set the appropriate density; if it is high, the copy density adjustment will be too fine and will not be sufficient. It was not possible to change the concentration.

〔the purpose〕

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to uniformize the copy density by changing the correction rate according to the relative resolution.

〔Example〕

The present invention will be further explained below.

That is, in the present invention, the constant (K) in the above-mentioned equation, ie, correction factor=constant (K) x scale amount (N), is not set to a constant value, but is changed depending on the contrast.

FIG. 1 is a graph showing the relationship between contrast and one scale constant a (K). If the contrast value of the image is small, or if the small characters are image information, reduce the correction factor by decreasing the 1 scale constant (K), while if the large characters are the image information. When such a contrast value is large, the one scale constant (K) is increased to increase the correction factor.

FIG. 2 is a diagram showing the relationship of threshold correction when the contrast (amplitude) of an image is large. ΔX indicates the amount of change in the threshold value when the threshold value (a) changes by one scale step.

Moreover, FIG. 3 is a diagram showing the relationship of threshold value correction when the contrast (amplitude) of an image is small. As shown in the figure, the amount of threshold change in one scale step for a small amplitude image is ΔX'. In this way, the amount of threshold change per step, ΔX, is made larger when the contrast is dog than when the contrast is small.

FIG. 4 shows a block diagram of an image signal quantization circuit to which the present invention is applied, in which 1 is a density setting section as shown in FIG. 5 for setting the density by the operator, and 2 is the contrast of the image to be read. A contrast detection section that detects
3 is a CCD sensor that photoelectrically reads a film image; 4 is a threshold value setting unit that generates a threshold value for quantizing the output of the CCD sensor 3, such as binarization; 5 is a CCD sensor 3
This is a comparator for binarizing the output from the threshold value setting section 4 using the threshold value. The threshold value setting section 4 uses the step value from the density setting section 1 and the contrast value from the contrast detection section 2 to set and output a threshold value using a correction rate according to the contrast value as described above.

As mentioned above, by changing the one scale constant of the copy density adjustment scale depending on the contrast (amplitude) of the image, images of large character group information and images of small character group information can be adjusted per division of the copy density adjustment scale. This makes it possible to make appropriate copy density adjustments.

Note that the contrast of the image is detected using the output of a CCD sensor for image reading, or is manually set by the operator.

(Effects) As described above, according to the present invention, the threshold value can be corrected according to the contrast of the image, so it is possible to obtain a desired read output according to the contrast.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the 1-scale constant characteristic, Fig. 2 is a diagram showing the 1-scale threshold change amount at large amplitude, Fig. 3 is a diagram showing the 1-scale threshold change amount at small amplitude, and Fig. 4 is a diagram showing the 1-scale threshold change amount at large amplitude. FIG. 5 is a block diagram of a quantization circuit to which the present invention is applied, and is an external view of an image density setting section, in which 1 is a density setting section, 2 is a contrast detection section, 3 is a CCD sensor, 4 is a threshold setting section, 5 is a comparator.

Claims (1)

[Claims] 1. A threshold correction method characterized by varying a threshold correction rate for reading and quantizing an image recorded on a film depending on image contrast.