IMAGE PROCESSING APPARATUS AND CONTROL METHOD

• US 20100260417A1
• Filed: 03/31/2010
• Published: 10/14/2010
• Est. Priority Date: 04/13/2009
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Dai, Xiaoyan
• Granted Patent: US 8,401,306 B2
• Time in Patent Office: Days
• US Class Current: 382/165
• CPC Class Codes: G06V 30/10 Character recognition
• CPC Class Codes: G06V 30/162 Quantising the image signal
• CPC Class Codes: G06V 30/413 Classification of content, e.g. text, photographs or tables
• CPC Class Codes: H04N 1/40062 Discrimination between different image types, e.g. two-tone, continuous tone

Abstract

An image processing apparatus includes a block background/foreground determination unit which determines, based on a block attribute and quantized color information, whether each connected area is a foreground or a background, a block background/foreground attribute determination unit which determines, based on the block attribute, the attribute of a connected area determined to be the foreground of the block and the attribute of a connected area determined to be the background of the block, and a block background/foreground attribute information recording unit which records and holds information of the attribute of the block and the attribute of each connected area.

Claims

1. An image processing apparatus comprising:

a block attribute determination unit which determines, for each block including a predetermined number of pixels of a document image, an attribute of the block based on edge features of the block;

a block color quantization unit which quantizes color information of each pixel of the block including the predetermined number of pixels of the document image;

a block connected area extraction unit which extracts, based on the color information of each pixel quantized by said block color quantization unit, connected areas each included in the block and including connected pixels of the same color;

a block background/foreground determination unit which determines whether each connected area is a foreground or a background, based on the block attribute determined by said block attribute determination unit, the color information quantized by said block color quantization unit, and the connected areas acquired by said block connected area extraction unit;

a block background/foreground attribute determination unit which determines, based on the block attribute determined by said block attribute determination unit, an attribute of a connected area determined by said block background/foreground determination unit to be the foreground of the block and an attribute of a connected area determined to be the background of the block; and

a block background/foreground attribute information recording unit which records and holds information of the attribute of the block determined by said block attribute determination unit and the attribute of each connected area determined by said block background/foreground attribute determination unit.

2. The apparatus according to claim 1, wherein the edge features are the number of edge pixels included in the block, the number of connected edges formed from the edge pixels, and the number of edge pixels included in a connected area formed from the edge pixels.

3. The apparatus according to claim 1, wherein the block attribute is one of a halftone dot block formed from halftone dot pixels, a background block formed from background pixels, a character block on background area formed from background pixels and character pixels, and a character block on halftone dot area formed from halftone dot pixels and character pixels.

4. The apparatus according to claim 3, where in

said block attribute determination unit has

a first threshold for the number of edge pixels included in the block,

a second threshold for the number of connected edges included in the block, and

a third threshold for the number of pixels of a connected area included in the block,

if the number of edge pixels included in the block is not more than the first threshold, said block attribute determination unit determines the block attribute as background,

if the number of edge pixels included in the block is less than the first threshold, and the number of connected edges is less than the second threshold, said block attribute determination unit determines the block attribute as character on background area,

if the number of edge pixels included in the block is less than the first threshold, the number of connected edges is not less than the second threshold, and there is no connected edge whose number of pixels is not less than the third threshold, said block attribute determination unit determines the block attribute as halftone dot, and

if the number of edge pixels included in the block is less than the first threshold, the number of connected edges is not less than the second threshold, and there is a connected edge whose number of pixels is not less than the third threshold, said block attribute determination unit determines the block attribute as character on halftone dot area.

5. The apparatus according to claim 3, wherein

said block attribute determination unit has

a first threshold for the number of edge pixels included in the block,

a second threshold for the number of connected edges included in the block, and

a third threshold for an edge feature difference between the block and an adjacent peripheral block,

if the number of edge pixels included in the block is not more than the first threshold, said block attribute determination unit determines the block attribute as background,

if the number of edge pixels included in the block is more than the first threshold, and the number of connected edges is not less than the second threshold, said block attribute determination unit determines the block attribute as halftone dot,

if the number of edge pixels included in the block is more than the first threshold, and the number of connected edges is less than the second threshold, a difference between the edge features of the block and edge features of the peripheral block is obtained, and if the difference is not more than the third threshold, said block attribute determination unit makes the block attribute equal to an attribute of the peripheral block,

if the number of edge pixels included in the block is more than the first threshold, the number of connected edges is less than the second threshold, the difference is more than the third threshold, and the attribute of the peripheral block is halftone dot, said block attribute determination unit determines the block attribute as character on halftone dot area,

if the number of edge pixels included in the block is more than the first threshold, the number of connected edges is less than the second threshold, the difference is not less than the third threshold, and the attribute of the peripheral block is character on halftone dot area, said block attribute determination unit determines the block attribute as halftone dot,

if the number of edge pixels included in the block is more than the first threshold, the number of connected edges is less than the second threshold, the difference is not less than the third threshold, and the attribute of the peripheral block is background, said block attribute determination unit determines the block attribute as character on halftone dot area, and

if the number of edge pixels included in the block is more than the first threshold, the number of connected edges is less than the second threshold, the difference is not less than the third threshold, and the attribute of the peripheral block is character on halftone dot area, said block attribute determination unit determines the block attribute as background.

6. The apparatus according to claim 5, wherein the peripheral block is one of a block adjacent to a left side of a process target block and a block adjacent to an upper side of the process target block.

7. The apparatus according to claim 1, wherein said block color quantization unit performs tone reduction to generate one of binary data and multilevel data of the pixels of the block.

8. The apparatus according to claim 1, wherein

said block background/foreground determination unit acquires, as a background color, a color of a block whose attribute has been determined by said block attribute determination unit as one of background and halftone dot, and

if a color of the connected area included in the block whose attribute has been determined as one of character on background area and character on halftone dot area is different from the background color, said block background/foreground determination unit determines the connected area as the foreground.

9. The apparatus according to claim 1, wherein

based on the block attribute determined by said block attribute determination unit and a result of the connected area determined by said block background/foreground determination unit,

said block background/foreground attribute determination unit determines the background of the block as halftone dot if the block attribute is one of halftone dot and character on halftone dot area,

determines the background of the block as background if the block attribute is one of background and character on background area,

determines the connected area determined to be the foreground of the block as character on background area if the block attribute is character on background area, and

determines the connected area determined to be the foreground of the block as character on halftone dot area if the block attribute is character on halftone dot area.

10. The apparatus according to claim 1, wherein said block attribute determination unit further comprises a block attribute modification unit which corrects the block attribute based on the edge features and the color information acquired by said block color quantization unit.

11. The apparatus according to claim 10, wherein

said block attribute modification unit modifies the block attribute to background if the number of main colors of color quantization of the block is 1, and the block attribute is character on background area, and

modifies the block attribute to halftone dot if the number of main colors of color quantization of the block is 1, and the block attribute is character on halftone dot area.

12. A control method comprising:

a block attribute determination step of causing a block attribute determination unit of an image processing apparatus to determine, for each block including a predetermined number of pixels of a document image, an attribute of the block based on edge features of the block;

a block color quantization step of causing a block color quantization unit of the image processing apparatus to quantize color information of each pixel of the block including the predetermined number of pixels of the document image;

a block connected area extraction step of causing a block connected area extraction unit of the image processing apparatus to extract, based on the color information of each pixel quantized in the block color quantization step, connected areas each included in the block and including connected pixels of the same color;

a block background/foreground determination step of causing a block background/foreground determination unit of the image processing apparatus to determine whether each connected area is a foreground or a background, based on the block attribute determined in the block attribute determination step, the color information quantized in the block color quantization step, and the connected areas acquired in the block connected area extraction step;

a block background/foreground attribute determination step of causing a block background/foreground attribute determination unit of the image processing apparatus to determine, based on the block attribute determined in the block attribute determination step, an attribute of a connected area determined in the block background/foreground determination step to be the foreground of the block and an attribute of a connected area determined to be the background of the block; and

a block background/foreground attribute information recording step of causing a block background/foreground attribute information recording unit of the image processing apparatus to record and hold information of the attribute of the block determined in the block attribute determination step and the attribute of each connected area determined in the block background/foreground attribute determination step.

13. A computer-readable medium storing a program which causes a computer to function as:

a block attribute determination unit which determines, for each block including a predetermined number of pixels of a document image, an attribute of the block based on edge features of the block;

a block color quantization unit which quantizes color information of each pixel of the block including the predetermined number of pixels of the document image;

a block connected area extraction unit which extracts, based on the color information of each pixel quantized by said block color quantization unit, connected areas each included in the block and including connected pixels of the same color;

a block background/foreground determination unit which determines whether each connected area is a foreground or a background, based on the block attribute determined by said block attribute determination unit, the color information quantized by said block color quantization unit, and the connected areas acquired by said block connected area extraction unit;

a block background/foreground attribute determination unit which determines, based on the block attribute determined by said block attribute determination unit, an attribute of a connected area determined by said block background/foreground determination unit to be the foreground of the block and an attribute of a connected area determined to be the background of the block; and

a block background/foreground attribute information recording unit which records and holds information of the attribute of the block determined by said block attribute determination unit and the attribute of each connected area determined by said block background/foreground attribute determination unit.