JPH03139973A - Original reader for facsimile - Google Patents

Abstract

PURPOSE:To secure the black width of a binary slice level even if the light quantity is changed by updating a peak value limit in accordance with the output level of an image signal and setting up the peak value limit always to a prescribed rate between black and white levels. CONSTITUTION:When the whole peak value is increased, the peak value limit 12 is updated by a peak value limit setting circuit 4. A peak value setting circuit 5 sets up the peak value 10 of an image part as a peak value, but when the peak value is approached to the black level exceeding the peak value limit, sets up the peak value limit as the peak value. A binary slice level setting circuit 6 divides the set peak value 13 and sets up a slice level to be a boundary for recognizing white and black and a comparator 7 compares an image signal 8 with slice level 14 and outputs the binarization data of the image signal. Since the peak value limit is set up to a prescribed rate between the black and white levels, the black width of the binary slice level can be secured even if the light quantity is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a facsimile document reading device, and more particularly to a facsimile document reading device that binarizes an image signal.

[Conventional technology]

Conventionally, the binarization circuit of this type of facsimile document reading device operates to set the peak value limit only once before reading the document.

[Problem to be solved by the invention]

The binarization circuit of the conventional facsimile original reading device described above has a setting operation in which the peak value limit is set once before reading the original, so as shown in Figure 3, As the amount of light increases during the period from a cold state to a stable state, the peak value limit set before reading is too small, and as shown in Figure 4(c), the peak value limit and black level are reversed. Where the peak value reaches the peak value limit, the black side of the binarized slice level cannot be ensured, and there is a drawback that continuous black signals are binarized as the white level.

[Means to solve the problem]

The facsimile document reading device of the present invention includes a peak value detection circuit that detects the peak value of the white level of an image signal read from the document to be transmitted, and a peak value limit that limits the approach of the peak value to the black level of the image signal. a peak value limit setting circuit that varies the peak value limit according to the output of the peak value limit, and a beat value setting circuit that sets the peak value limit to the value of the peak value limit when the detected peak value is closer to the black level than the peak value limit; A binarization slice level setting circuit sets a reference slice level when dividing and binarizing the set peak value, and compares the image signal with the binarization slice level. and a comparator that outputs valued data.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

The image signal 8 read by the reading circuit 1 is determined by the peak value detection circuit 2 to have a peak value 10 of the image portion within the range defined by the peak value detection interval signal 9, and the overall peak value by the peak value detection circuit 3. 11 is detected. When the overall peak value increases, the peak value limit setting circuit 4 updates the peak value limit 12. The peak value setting circuit 5 sets the peak value 10 of the image portion as the peak value, but when the black level is closer than the peak value limit, the peak value limit is set as the peak value.

The binarization slice level setting circuit 6 divides the set peak value 13 and sets a slice level at which black and white are recognized. A comparator 9 compares the image signal 8 and the slice level 14 and outputs binarized data of the image signal.

FIG. 2 is a flowchart for explaining the operation of the peak value limit setting circuit 4 shown in FIG. The peak value P is read out in step 21, and compared with the previous peak value P' in step 22. If the peak value becomes larger, the setting of the peak value limit is updated in steps 23-25. This operation is performed at predetermined intervals of 1 second in step 26.

FIG. 3 shows the change in the amount of light after the fluorescent lamp is turned on.

There is a large change in the amount of light at point A immediately after lighting and point B nearing a stable state.

FIGS. 4(a), 4(b), and 4(c) are waveform diagrams of image signals when a completely black screen at points A and B in FIG. 3 is scanned.

FIG. 4(a) shows the waveform of the image signal immediately after the fluorescent lamp is turned on. Reference numeral 41 indicates the peak value of the image signal, which is a value detected within the peak value detection section of 44. Since there is no white level in the peak value detection section 44, the peak value 41 gradually changes from the white level 45 toward the black level 46 of the original as the original is scanned. 42 is the entire peak value detected including the shading portion of the white line. 43 is a peak value limit, and the peak value 41 of the image signal can be brought close to the black level up to this value.

FIG. 4(b) shows the waveform of the image signal when the fluorescent lamp warms up and the amount of light increases. Since the amount of light increases, the amplitude increases and the overall peak value 42 increases. in this way,
When the overall peak value becomes large, the peak value limit is set to a predetermined ratio between the black level and the white level.

〔Effect of the invention〕

As explained above, the present invention updates the peak value limit according to the output size of the image signal and always sets the peak value limit to a predetermined ratio between the black level and the white level. When the light warms up and the light intensity changes,
Even if the peak value follows up to the peak value limit, there is an effect that the black width at the binarized slice level can be secured.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
FIG. 3 is a flowchart for explaining the operation of the peak value limit setting circuit shown in FIG. (b) and (c) are waveform diagrams of image signals at points A and B in FIG. 3. 1... Reading circuit, 2, 3... Peak value detection circuit, 4... Peak value limit setting circuit, 5... Peak value setting circuit, 6・・・・・・
Binarization slice level setting circuit.

Claims (1)

[Claims] a peak value detection circuit that detects the peak value of the white level of an image signal read from a document to be transmitted; and a peak value limit that limits the proximity of the peak value to the black level and varies the peak value limit according to the output of the image signal. a setting circuit,
A peak value setting circuit that sets the value of the peak value limit when the detected peak value is closer to the black level than the peak value limit, and a peak value setting circuit that divides the set peak value into two.
Setting the slice level that is the standard when converting values 2
A facsimile document reading device comprising: a digitized slice level setting circuit; and a comparator that compares the image signal with the binarized slice level and outputs binarized data of the image signal.