JP2584747B2 - Image processing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus that converts an input image into an output image by comparing the input image with a threshold value, and in particular, can set the density of the output image arbitrarily and change the threshold value accordingly. The present invention relates to an image processing apparatus for performing the above.

(Prior art)

FIG. 5 shows an image density correction unit 40 provided in the image reading apparatus.
A lever 41 is provided which is manually moved corresponding to a copy density correction scale that changes in steps for each scale. By moving the lever 41, a threshold value for quantizing the read output is set. to correct. Conventionally, the correction rate for correcting the threshold value is calculated by the following equation: correction rate = constant (K) × −scale amount (N), and by setting K to a constant value, the correction rate has linearity. Even small characters were corrected at the same correction rate, and the copy density was manually adjusted.

However, if the relative resolution of the characters (the resolution per character) is low, the copy density adjustment is coarse, and it is not possible to set an appropriate density, and if the relative resolution is high, the copy density adjustment is too fine. The density could not be changed.

〔Purpose〕

The present invention eliminates the above-mentioned disadvantages of the prior art. The density of an output image can be set to an arbitrary step by a setting unit, and a threshold value is changed according to the set step, and the contrast of an input image is reduced. By changing the amount of change of the threshold value for one step of the setting means in response, the output image density can be appropriately changed according to the setting of the setting means, regardless of the difference in the contrast of the input image.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, the constant (K) in the above equation, that is, correction rate = constant (K) × scale (N), is not set to a constant value but is changed according to the contrast.

FIG. 1 is a graph showing the relationship between contrast and one scale constant (K). When the contrast value of the image is small, or when a small character is image information, the correction factor is reduced by reducing the one scale constant (K),
On the other hand, when the contrast value is large such that a large character is image information, the scale factor (K) is increased to increase the correction rate.

FIG. 2 is a diagram showing the relationship of threshold value correction when the contrast (amplitude) of an image is large. Δx indicates the amount of change of the threshold value when one graduation step changes from the threshold value (a).

FIG. 3 is a diagram showing a relation of threshold value correction when the contrast (amplitude) of the image is small. As shown in the figure, the threshold change amount of one scale step for a small-amplitude image is △ x ′. As described above, the threshold change amount per step, Δx, is set to be larger when the contrast is larger than when the contrast is small.

FIG. 4 is a block diagram of a quantization circuit for an image signal to which the present invention is applied, wherein 1 is a density setting section for setting density by an operator as shown in FIG. A contrast detector for detecting,
3 is a CCD sensor for photoelectrically reading a film image, 4 is a CCD sensor
A threshold setting unit that generates a threshold for quantizing the output of the sensor 3, for example, as binarization, 5 is a comparator for binarizing the output of the CCD sensor 3 using the threshold from the threshold setting unit 4. is there. The threshold value setting unit 4 sets and outputs a threshold value using the step value from the density setting unit 1 and the contrast value from the contrast detection unit 2 using the correction rate according to the contrast value as described above.

As described above, by changing one scale constant of the copy density adjustment scale according to the magnitude of the contrast (amplitude) of the image, both the image of the large character group information and the image of the small character group information can be changed per one scale of the copy density adjustment scale. , The density difference was made uniform, and appropriate copy density adjustment became possible.

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

(Effect)

As described above, according to the present invention, the density of the output image can be set to an arbitrary step by the setting means, the threshold value is changed according to the set step, and one step of the setting means is set according to the contrast of the input image. , The output image density can be appropriately changed in accordance with the setting of the setting unit, regardless of the difference in the contrast of the input image.

[Brief description of the drawings]

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

Claims (1)

(57) [Claims] An input unit configured to input an image; a threshold setting unit configured to set a threshold when performing threshold processing on the image input by the input unit; and an image input by the input unit set by the threshold setting unit. A conversion unit that compares the output image with the threshold value and converts the output image into an output image; and a setting unit that sets the density of the output image to an arbitrary one of a plurality of steps. An image processing apparatus for changing a threshold value to change an output density by changing a threshold value for one step of the setting means according to a contrast of an input image.