Method for setting black reference data used for excess exposure, and image reading apparatus

• US 20020171820A1
• Filed: 04/29/2002
• Published: 11/21/2002
• Est. Priority Date: 08/30/2000
• Status: Active Grant

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Okamura, Yukio
• Granted Patent: US 7,031,029 B2
• Time in Patent Office: Days
• US Class Current: 355/133
• CPC Class Codes: H04N 1/4076 dependent on references outside the picture

Abstract

By performing preliminary scanning, a document identification unit determines whether a document is a dark document, such as a negative film, that requires excess exposure, or an ordinary document that does not require excess exposure. When it is determined that the document does not require excess exposure, an exposure time setting unit sets an exposure time for a line sensor. Then, in consonance with the designated exposure time, the line sensor initiates the reading of a black reference. Thereafter, in accordance with an excess exposure time that is designated, a black reference data preparation unit prepares black reference data. Since the black reference is read during the same period as the excess exposure time and the black reference data is prepared, the detailed tones of the dark portion of the document can be expressed, and the quality of the image can be improved.

Claims

1. A black reference data setting method for an image pickup device receiving light from a light source, and outputting an electric signal for setting black reference data used for excess exposure in accordance with the amount of received light, the method comprising a step of:

reading, when an exposure time for the image pickup device is n times a basic exposure time, a black reference during a period that is n times a period of the basic exposure time.

2. A black reference data setting method for excess exposure comprising:

reading an outline of a document by an image pickup device having multiple pixels;

setting a gamma curve that is consonant with the document based on a value of an electric signal outputted from the image pickup device at the reading step;

determining whether the gamma curve is included in a predetermined area;

determining a constant c constituting a magnification rate along an output axis of the gamma curve so that the gamma curve is included in the predetermined area;

setting the exposure time for the image pickup device to constant c times the basic exposure time when determination that the gamma curve is outside the predetermined area is made; and

reading a black reference in accordance with the exposure time set at the setting step, and preparing black reference data.

3. The method according to claim 2, wherein the black reference data are prepared for each pixel constituting the image pickup device.

4. An image reading apparatus comprising:

a light source for projecting light onto a document;

an image pickup device for receiving-light from said document and for outputting an electric signal that is consonant with the amount of light that is received;

a document identification unit for determining whether the document is an excess exposure document requiring excess exposure based on the electric signal output from the image pickup device;

an exposure time setting unit for, when the document identification unit determines that the document is an excess exposure document, setting an exposure time for the image pickup device that is a predetermined number times a basic exposure time; and

a black reference data preparation unit for permitting the image pickup device to read a black reference so that an exposure time for reading the black reference is equal to the exposure time set by the exposure time setting unit, and for preparing black reference data.