Image scanning device and calibration method thereof

Abstract

In a calibration method of an image scanning device, an original for use calibration including a plurality of patches each having a different tone is scanned, scanned tone values of the patches of the original are acquired with respect to each of a plurality of color components, a curve function is acquired with respect to each of the plurality of color components based on the scanned tone values and target tone values of the patches predetermined with respect to each of the plurality of color components, each curve function approximating a relationship between an input defined as the scanned tone value and an output defined as the target tone value, and the curve function is acquired with respect to each of the plurality of color components such that input value intercepts, each being defined as an upper limit of a range of the input value in which range the output value is maintained at zero, are equal among the plurality of color components.

Description

technical field [0001] The present invention relates to an image reading device capable of reading a document into three color components (such as red, green, and blue RGB components) to obtain a read image and a calibration method thereof. Background technique [0002] A conventional digital color copier has a charge-coupled device (CCD) line image sensor as an image acquisition unit, and reads an image of reflected light from a document as an analog signal of a colorimetric system represented by RGB. Image data generated from an analog [analog] signal read by a CCD linear image sensor is sent to an analog front end (AFE) and converted into digital data [digital data]. The image data output from the AFE is multi-valued image data representing the R component, G component, and B component of each pixel by 8-bit data. [0003] This conventional digital color copier has a calibration mode. In this calibration mode, the copier uses the CCD linear image sensor to read the reco...

AI Technical Summary

Problems solved by technology

However, especially when it is desired to create a calibration document with an appropriate color sample and density in a low-brightness gradation, it is necessary to print at a high density, and the cost [cost] increases

[0005] Regarding this point, when a test image is printed on a recording sheet by a copier for calibration as conventionally shown, it is difficult to accurately form the portion of the low-brightness gradation recorded on the recording sheet to an expected density.

Therefore, if the correction parameters are calculated without considering the luminance in the calibration mode, the reproducibility (gray balance) of the gradation in low luminance is likely to deteriorate, and it is difficult to read from the viewpoint of image quality. room for improvement

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