JPH04250770A - Picture reader - Google Patents

Abstract

PURPOSE:To eliminate the need for detecting a white level in an original and to simplify an analog circuit for the share by comparing a white level of a white color face with a white level of an original, and fixing a signal with a higher level as a reference so as to implement picture processing. CONSTITUTION:An image sensor 1 outputs a picture signal 2a read from an original 1c carried by rollers 1a, 1b and a white level signal 2b read from a white level reference board 1e provided to a read position in precedence over the read of the original 1c to a switch 5. A peak detection circuit 6 compares a white level 3 of the picture signal 2a with a white level 4 of the white level signal 2b and outputs a higher level as a reference white level 7. An A/D converter 8 A/D converts the picture signal in response to the reference white level 7.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device used in facsimiles, image scanners, etc.

0002

2. Description of the Related Art When a conventional image reading device reads an image using an image sensor, it detects the white level of a roller or the like that sets the reference white, sets it as the white level, and then simultaneously reads the image signal. The dynamic range was changed by following the set white level according to the white level in the original document.

0003

[Problems to be Solved by the Invention] In the conventional image reading device described above, white level detection of the image sensor requires
At the same time as reading the image signal, a complex analog circuit was required to follow the set white level according to the white level in the document being read.

0004

[Means for Solving the Problems] An image reading device of the present invention includes an image sensor that outputs an image signal read from a document and a white signal read from a white surface provided at a reading position prior to reading the document. and a peak detection circuit that compares the white level of the image signal with the white level of the white signal and outputs the higher one as a reference white level.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention, FIGS. 2 and 3
FIG. 2 is a diagram for explaining the operation of this embodiment.

In FIG. 1, an image sensor 1 receives an image signal 2a read from a document 1c conveyed by rollers 1a and 1b, and a white signal read from a white plate 1e provided at a reading position prior to reading the document 1c. 2b is output to switch 5. The peak detection circuit 6 detects the image signal 2
The white level of the signal a and the white level of the white signal 2b are compared, and the higher one is outputted as the reference white level 7. The A/D converter 8 performs A-D conversion of the image signal according to the reference white level 7.

FIG. 2 shows that when the peak detection circuit 6 detects the white level and the white level 4 of the white signal 2b is higher than the white level 3 of the image signal 2a, the white level 4 of the white signal 2b is used as the reference white. 3 shows that when the white level is detected and the white level 4 of the white signal 2b is lower than the white level 3 of the image signal 2a, the white level 3 of the image signal 2a is used as the reference. This indicates that the white level is output as 7.

In this way, in the image signal 2a read from the original 1c by the image sensor 1, peak detection is performed by turning on the switch 5 to detect the white level 4 of the white plate 1e and the white level 3 inside the original before reading the original. The signal is sent to the circuit 6, the peak detection circuit 6 compares the two, and the higher white level is set as the reference white level 7 and sent to the A/D converter 8.
Enter. In the A/D converter 8, the reference white level 7
The image signal 2a can be A/D-converted using the maximum value of the dynamic range.

Although this embodiment has been described using the white plate 1e, the roller 1b may have a white surface.

0010

As explained above, the present invention compares the reference white level of the white surface with the white level of the original, and performs image processing by fixing the higher signal as the reference. White level detection becomes unnecessary, and the analog circuit can be simplified accordingly.

[Brief explanation of the drawing]

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

FIG. 2 is a diagram for explaining the operation of this embodiment.

FIG. 3 is a diagram for explaining the operation of this embodiment.

[Explanation of symbols]

1 Image sensor 2a Image signal 2b White signal 3. Image signal white level 4 White level of white signal 5 Switch 6 Peak detection circuit 7 Standard white level 8 A/D converter

Claims (2)

[Claims] 1. An image sensor that outputs an image signal read from a document and a white signal read from a white surface provided at a reading position prior to reading the document, and a white level of the image signal and the white signal. 1. An image reading device comprising: a peak detection circuit that compares the white level of the white level and outputs the higher one as a reference white level. 2. The image reading device according to claim 1, wherein the image signal is converted from analog to digital based on the reference white level.