1. Field of the Invention
Aspects of the present invention relate to an image forming apparatus and a method for controlling the same, which analyze image data to automatically and discriminately detect whether the image should be printed in color or with pure black.
2. Description of the Related Art
Image forming apparatuses, such as a digital multi-function printer (DMFP) and a copy machine, may obtain an image through a scanning operation of a sensor or receive the image from an external device, such as a host computer. In addition, in the image forming apparatuses, the obtained image is subject to color-coordinate transformation so that the image may be printed by a printer engine.
FIG. 1 shows an example image forming apparatus. Such an image forming apparatus includes an image input unit 10, an image processing unit 20, a storage unit 30, and a printer engine 40. Referring to FIG. 1, an image input unit 10 provides red, green, and blue (RGB) data of a document image to an image processing unit 20. Here, as an example, the image input unit 10 obtains a scanned image using an image sensor, such as, a charge coupled device (CCD) or a contact image sensor (CIS).
The image processing unit 20 includes a memory 21 to store the RGB data of the document image, a color coordinate transformer 22 to transform the RGB data received from the memory 21 into cyan, magenta, yellow, and black (CMYK) data for printing, and a binary converter 23 to convert the CMYK data into binary CMYK data. The binary CMYK data on a printable medium converted by the image processing unit 20 is provided to a printer engine 40 through a storage unit 30. The printer engine 40, having received the CMYK data, prints the CMYK data so as to reproduce the image.
When the image processing unit 20 performs the color coordinate transformation, a portion of a black-and-white image may be erroneously converted into a color image due to characteristics of sensors used for obtaining an image. In such case, a printed result may have color components different from those of an original image. For this reason, when black letters are printed, color components may exist thereby degrading readability of the printed result. When a user inputs a color printing command, even though an image includes only black letters, the image forming apparatus uses a composite black color in order to print the image on a printable medium. However, the composite black deteriorates the readability of the printed result as compared to a pure black color.
When an image forming apparatus equipped with an auto-document feed (ADF) function duplicates color documents together with black-and-white documents, the user must manually set the color types of the documents to be duplicated thereby causing inconvenience to the user. For this reason, a method of performing printing operations by automatically detecting the type of the documents is necessary.
Japanese Unexamined Patent Publication No. 9-277606 discloses a color printer which prints input color data using only black color when RGB components of the input color data have the same value. However, according to this conventional method, if a black-and-white document has a color stain, such as, a thin line drawn by a red pen, the black-and-white document cannot be completely reproduced. Accordingly, RGB component must be inspected with respect to all pixels in the image data of the document.