Provided are an image composition apparatus for composing color images with black-and-white images including infrared components, and an image composition method thereof The image composition method includes generating a first image signal with color information and a second image signal including infrared components without color information, dividing the first image signal into a brightness signal and a color signal, composing the brightness signal of the first image signal with a brightness signal of the second image signal to generate a composed brightness signal, and composing the composed brightness signal with the color signal of the first image signal to generate a color image.

A gain modification device (20) includes a plurality of gain modification units (31) whose number of units corresponds to a number of kinds of a plurality of signals input to the plurality of gain modification units, each one of the plurality of gain modification units (31) being configured to modify a gain value used to amplify the plurality of signals, and a plurality of gain reflection control units (44) configured to change a timing at which the gain value is to be switched by the plurality of gain modification units (31) such that the gain value of one of the plurality of signals affecting a signal level of another one of the plurality of signals is switched at a timing different from a timing at which the gain value of the another one of the plurality of signals is switched.

A gain modification device (20) includes a plurality of gain modification units (31) whose number of units corresponds to a number of kinds of a plurality of signals input to the plurality of gain modification units, each one of the plurality of gain modification units (31) being configured to modify a gain value used to amplify the plurality of signals, and a plurality of gain reflection control units (44) configured to change a timing at which the gain value is to be switched by the plurality of gain modification units (31) such that the gain value of one of the plurality of signals affecting a signal level of another one of the plurality of signals is switched at a timing different from a timing at which the gain value of the another one of the plurality of signals is switched.

An image reading apparatus includes: a reader that reads an image formed on a print medium; and a backing part that is disposed at a position facing the reader and is capable of switching a color of a portion to be a background of the print medium upon reading by the reader to a plurality of colors according to a type of the print medium and/or a color read from the print medium.

An illumination device includes a light guide member having a first side in a main scanning direction and a second side in a sub-scanning direction and a plurality of light sources including first light emitters respectively to emit beams of light of a first color and a second light emitter to emit a beam of light of a second color different from the first color toward an inside of the light guide member via a side of the light guide member in the main scanning direction. The first light emitters are positioned in the sub-scanning direction to be symmetrical to each other.

An image processing portion of an image reading apparatus includes an extraction portion that extracts color information, a management portion that manages management color information that is an estimated value of the color information based on a control signal, a determination portion that determines whether or not the color information matches the management color information, and a writing control portion that causes the storage portion to store the pixel data when it is determined that the color information matches the management color information and that does not cause the storage portion to store the pixel data when it is determined that the color information does not match the management color information. When the color information does not match the management color information, the management portion adjusts the management color information to match the color information.

An original image is read as an aggregate of a plurality of pixels in which adjacent pixels have different colors (R, G, and B) in a main scanning direction and in a sub-scanning direction, and the read pixels of the respective colors are stored in a line memory in association with information on relative positions of the pixels with respect to another pixel. Then, the stored pixels are sorted so that pixels having the same color are adjacent to each other, and an abnormal pixel (dust) not present in the original image is detected based on the state of the sorted pixels. With this, the dust not present in the original image is detected without increasing the cost, and the dust is corrected without forming a conspicuous trace of correction.

An image reading apparatus includes a front-side reader, which includes a white LED configured to irradiate an original with light and a CMOS sensor configured to receive light that is reflected by the original. The front-side reader is configured to generate read data that represents a luminance value of an image on the original from the result of receiving light with the CMOS sensor. The image reading apparatus stores, in a non-volatile memory, a condition for determining whether there is a sub-scanning color shift, and uses a sub-scanning color shift detector to determine whether there is a sub-scanning color shift based on the read data obtained from the front-side reader and the condition stored in the non-volatile memory. When there is a sub-scanning color shift, the image reading apparatus corrects the sub-scanning color shift by correcting the read data with a color shift corrector.

An image processing device performing color balancing of a first image and at least a second image is provided. The image processing device comprises a color balancing determination unit and a color balancing calculation unit.

The color balancing determination unit determines a global gain vector (t) comprising at least two gain factors (â.sup.n, â.sup.n+1) of the first and second images by minimizing a cost function based upon reference pixel values of the first and second images. The first and second image reference pixels depict a shared color scene of the two images.

The color balancing calculation unit performs color balancing of the first image based upon the gain factor (â.sup.n) of the first image and to perform a color balancing of the second image based upon the gain factor (â.sup.n+1) of the second image.

An image reading apparatus is provided with: a reading processing unit which moves a reading unit, causes a light emitting unit to emit a first amount of light, reads an electric charge generated by a photoelectric conversion unit, and reads an image of a document placed on a document placing surface on the basis of the read electric charge; and a detection processing unit which causes a light emitting unit to emit a second amount of light greater than the first amount of light, reads an electric charge generated by the photoelectric conversion unit, and detects the size of the document placed on the document placing surface on the basis of the read electric charge.