JPH04326670A - Picture encoding device - Google Patents

Abstract

PURPOSE:To efficiently compress picture data while satisfactorily preserving the quality of characters and line drawings. CONSTITUTION:The decision result inputted from a signal line 101 is converted to raster scanning by a raster conversion circuit 14 for the purpose of improving the encoding efficiency and is encoded by an entropy encoding circuit 15 and is inputted to a multiplexing circuit 19. Extracted gradation data inputted from a signal line 102 is inputted to a change point detecting circuit 16 and a gradation table 17, and the change of extracted gradation data is detected by the change point detecting circuit 16. A gate circuit 18 is controlled in accordance with this change, and extracted gradation data is multiplexed by the multiplexing circuit 19.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding apparatus for encoding an input image, for example, an image in which characters, line drawings, etc. are synthesized with a natural image.

0002

2. Description of the Related Art Conventionally, as a method for encoding continuous tone natural images such as photographs, the image is divided into small blocks of 8×8 pixels, and discrete cosine transform (hereinafter referred to as DC
A method is known in which the coefficients are encoded after performing orthogonal transformation such as (denoted as T).

0003

[Problem to be Solved by the Invention] However, in the above conventional example, when encoding an image in which patterns artificially generated by a computer, such as characters and line drawings (graphics) are synthesized with a natural image, the background This has the disadvantage that sharp edges occur at the boundary between the natural image and the overwritten text/line drawings, resulting in a significant deterioration in the quality of the text/line drawings. In addition, when quantizing the coefficients after orthogonal transformation, the quantization step width of high-order coefficients is increased to match visual characteristics, which increases distortion of high-frequency components and causes deterioration such as ringing (mosquito noise) occurs,
There is also a drawback that encoding efficiency decreases.

The present invention has been made in view of the above-mentioned drawbacks, and it is an object of the present invention to provide an image encoding device that can efficiently compress image data while preserving the quality of characters and line drawings. purpose.

[0005]

Means and Effects for Solving the Problems In order to achieve the above object, an image encoding apparatus of the present invention has the following configuration. That is, an extraction means for extracting a line drawing based on gradation information of an input image, an encoding means for encoding the line drawing extracted by the extraction means, and an extraction means for encoding the line drawing extracted by the extraction means, and a and multiplexing means for multiplexing the gradation information according to the gradation information of the drawn line drawing.

[0006] Preferably, the method further comprises replacement means for replacing the gradation information of the line drawing extracted by the extraction means with a predetermined value, and encoding means for encoding the information from the replacement means. shall be.

[0007] More preferably, the multiplexing means has a detection means for detecting a change in tone information and a table for registering the tone information detected by the detection means, The gradation information registered in the table is multiplexed.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described in detail below with reference to the drawings. <First Embodiment> FIG. 1 is a schematic block diagram showing the configuration of an image encoding apparatus in a first embodiment. In the figure, 1
is an input terminal, into which image data is input from a computer (not shown) or the like. Reference numeral 2 denotes a character/line drawing extraction circuit which extracts characters/line drawings from image data and outputs gradation data and determination results, details of which will be described later. 3 is an encoding circuit, which encodes extracted characters and line drawings. Reference numeral 4 denotes an extracted pixel replacement circuit, which replaces pixels corresponding to extracted characters/line drawings with predetermined values. 5 is an encoding circuit, which encodes the replaced image data. A decoding circuit 6 decodes the data encoded by the encoding circuit 3. A decoding circuit 7 decodes the data encoded by the encoding circuit 5. A composing circuit 8 composes the data from the decoding circuits 6 and 7 with the original image data.

In the above configuration, the image data inputted from the input terminal 1 is processed by the character/line drawing extraction circuit 2, in which pixels corresponding to the characters/line drawings synthesized by a computer or the like are extracted, and the gradation data of the extracted pixels are extracted. (including color data of characters/line drawings) and the judgment result indicating whether the pixel is an extracted pixel (pixel extracted as a character/line drawing) (each pixel is 1 bit, in the example, it is set as “1” if it is an extracted pixel, otherwise it is output “0”) is input to the encoding circuit 3. The input judgment results are arithmetic encoded, Huffman encoded, MH, MR, MM
The data is encoded by an encoding circuit 3 having a known entropy encoding means suitable for encoding binary data such as R. In addition, the gradation data of the extracted pixel is multiplexed with the judgment result code encoded by the above-mentioned entropy encoding,
Output to the transmission line.

Next, the pixel data input to the extracted pixel replacement circuit 4 is converted into a value convenient for encoding (for example,
Average value, median value, mode value of pixels other than extracted pixels in the block,
or data interpolated from surrounding pixels of the extracted pixel, etc.) and input to the encoding circuit 5. The pixel data after replacement is JPEG (Joint Photography).
ADCT (Adaptive Coding) is a color still image coding method proposed by
ve Discrete Cosine Transf
orm), or DCT, DST (discrete sine transform), or the like, is encoded by an encoding circuit 5 having an encoding means suitable for encoding a multivalued image, and output to a transmission path.

Thereafter, the determination result of the extracted pixel and the gradation data of the extracted pixel transmitted from the above-mentioned encoding circuit 3 are decoded by the decoding circuit 6 and output to the synthesizing circuit 8. Furthermore, the image data transmitted from the encoding circuit 5 is
It is decoded by the decoding circuit 7 and output to the combining circuit 8. Then, in the synthesis circuit 8, when the determination result of the decoded extraction pixel described above is "1" (that is, the extraction pixel), the gradation data of the extraction pixel is selected, and the determination result is "1" (that is, the extraction pixel).
0'' (that is, other than the extracted pixel), the image data is selected and restored to the original input image signal.

Next, the detailed structure of the above-mentioned character/line drawing extraction circuit 2 will be explained below with reference to the block diagram shown in FIG.

First, the input image data is cut out by a blocking circuit 10 into small blocks of, for example, 8×8 pixels. Then, a histogram for each block is generated based on the extracted pixel data in the histogram generation circuit 11, and the result is output to the extracted pixel determination circuit 12. On the other hand, the image data input to the delay circuit 13 is output to the extracted pixel determination circuit 12 and the extracted pixel replacement circuit 4 after being delayed by the time necessary for the above-described histogram generation. Next, the extraction gradation is detected from the result of the input histogram in the extraction pixel determination circuit 12, and the image data input from the delay circuit 13 is compared with the above-mentioned extraction gradation. As a result, if they match, it is determined that the pixel is an extraction pixel, and "1" is output from the signal line 101 as a result of the determination, and "0" is output if they do not match.

Next, a method for detecting extracted gradations in this embodiment will be explained below with reference to FIG.

Since character/line drawing data added by a computer or the like has no correlation with the background, the gradation becomes discontinuous. In addition, the gradation of added characters and line drawings is usually
The data will be the same within a specific area. On the other hand, natural image data such as photographs have a strong correlation between pixels, and the distribution is widened due to noise being superimposed upon input, shading, etc. Therefore, the added character/line drawing data can be determined by detecting gradations in which there is no spread in the distribution of the generated histogram and the frequency is equal to or higher than the predetermined threshold Th. For example, when a histogram as shown in FIG. 3 is generated, gradation C is isolated with a nearby frequency of "0", and its frequency is also greater than the threshold Th, so that gradation C becomes the extraction gradation. becomes. Furthermore, although gradations A and D are also isolated, they are not determined as extracted gradations because they are infrequent and likely to be isolated points due to noise or the like.

The detailed configuration of the encoding circuit 3 to which the above-mentioned determination result and extracted gradation are input will now be described with reference to the block diagram shown in FIG. As mentioned above, the signal line 101
In order to improve encoding efficiency, the input judgment result is converted into raster scanning by the rasterization circuit 14,
The signal is input to the entropy encoding circuit 15. The data encoded by the entropy encoding circuit 15 is then input to the multiplexing circuit 19. Note that the entropy encoding circuit 15 is a known encoding circuit suitable for encoding binary data such as arithmetic encoding and Huffman encoding.

On the other hand, the extracted gradation data input from the signal line 102 is input to a change point detection circuit 16 and a gradation table 17, respectively. The change point detection circuit 16 controls the gate circuit 18 to open the gate of the gate circuit 18 if the input extracted gradation data is different from the data of the previous block, and to close the gate if they are the same. However, if there is no extracted pixel, they are considered to be the same. Furthermore, when the inputted gradation data is new, the gradation table 17 registers the gradation data on the table, and outputs the gradation data and the corresponding index to the gate circuit 18 . Furthermore, if the input data has already been registered, only the index is output to the gate circuit 18 without being registered.

Therefore, in the gate circuit 18, only when the extracted gradation data changes, the index (or gradation data) corresponding to the gradation data is input to the multiplexing circuit 19; and is multiplexed with the encoded determination result and transmitted. A conceivable method of multiplexing is, for example, to alternately send the coded determination results and gradation data every page or every n block lines. Further, the data may be multiplexed during transmission, or may be stored in separate memories during storage. usually,
Since the number of gradations of characters, line drawings, etc. used within the same page is extremely small, this configuration can significantly reduce the amount of transmitted data. Especially in the case of full color data, RGB each 8bi
Since the gradation data of t is 24 bits in total, the effect is tremendous.

Next, the extracted pixel replacement circuit 4 in the embodiment
The detailed configuration will be explained with reference to the block diagram shown in FIG.

First, the extraction determination result input from the signal line 101 is input to the replacement value generation circuit 20 and the delay circuit 22, and the input object line data input from the signal line 103 is input to the replacement value generation circuit 20 and the delay circuit 22. The signals are respectively input to the delay circuit 21. Here, the replacement value generation circuit 20 is a circuit that generates data to replace extracted pixel data, and generates data that improves encoding efficiency when the replaced image data is encoded by the encoding circuit 5. occurs. in particular,
A block average value, etc. of pixel data excluding extracted pixels is generated. The delay circuits 21 and 22 are circuits that delay the input image data and the extraction determination result by the time necessary to generate a replacement value, and each delayed signal is sent to the selector 23.
is input. According to the extraction determination result, the selector 23
If the input image data is an extracted pixel, the replacement value generation circuit 24
Otherwise, the image data of the delay circuit 21 is selected, and the data of the extracted pixel portion is replaced.

FIG. 6 is a block diagram showing the configuration of the synthesis circuit 8, in which a signal line 111 carries the extraction judgment result decoded by the decoding circuit 6, a signal line 112 carries the extracted gradation data, and It is assumed that image data decoded by the decoding circuit 7 is input to the signal line 113, respectively.

In the figure, the extracted gradation data and image data are converted into raster scanning by rasterizing circuits 24 and 25, respectively, and at the same time, the pixels at the same position as the pixels of the extraction judgment result inputted from the signal line 111 are The timing is adjusted and the signals are input to the selector 26 together. selector 26
Then, when the extraction determination result indicates an extracted pixel, the extracted gradation data is selected, and otherwise, the extracted pixel data is combined and restored to the input image data before replacement by selecting the image data.

As described above, according to the first embodiment, it is possible to efficiently compress image data while preserving the quality of characters and line drawings. <Second Embodiment> Next, a second embodiment according to the present invention will be described in detail below with reference to the drawings.

FIG. 7 is a schematic block diagram showing the configuration of an image encoding apparatus in the second embodiment. In the figure, components that perform the same functions as those in FIG. 1 are given the same reference numerals, and only points different from the first embodiment will be described.

As shown in FIG. 7, this embodiment is a case in which the image encoding device is applied to a page printer, and the transmission paths 121 and 122 in FIG.
7,28. In this configuration, the data encoded by the encoding circuits 3 and 4 are sequentially stored in the respective memories 27 and 28, and when one page's worth of data is stored, the printer engine (not shown) is started. be done. Here, a synchronization signal from the printer engine is input through the input terminal 31, and the decoding circuits 29 and 30 perform decoding in synchronization with the above-mentioned synchronization signal. As a result, output terminal 9
An image signal synchronized with the printer engine is output from the printer engine, and printing is executed.

According to the second embodiment, since characters are data compressed by entropy encoding, the font is not distorted and the quality of the characters is preserved. Also, since data such as characters and line drawings that are not suitable for orthogonal transformation are removed, the memory 28
capacity can be significantly reduced.

The present invention may be applied to a system composed of a plurality of devices such as a scanner, an interface, and a printer, or may be applied to an apparatus composed of a single device such as a copying machine. It goes without saying that the present invention can also be applied to a case where the present invention is achieved by supplying a program stored in a floppy disk or an ID card to a system or device, for example.

[0028]

[Effects of the Invention] As explained above, according to the present invention,
It is possible to efficiently compress image data while preserving the quality of characters and line drawings.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram showing the configuration of an image encoding device in a first embodiment.

FIG. 2 is a block diagram showing the configuration of a character/line drawing extraction circuit.

FIG. 3 is a diagram showing a generated histogram.

FIG. 4 is a block diagram showing the configuration of an encoding circuit.

FIG. 5 is a block diagram showing the configuration of an extracted pixel replacement circuit.

FIG. 6 is a block diagram showing the configuration of a synthesis circuit.

FIG. 7 is a schematic block diagram showing the configuration of an image encoding device in a second embodiment.

[Explanation of symbols]

2 Character/line drawing extraction circuit 3 Encoding circuit 4 Extracted pixel replacement circuit 5 Encoding circuit 6 Decoding circuit 7 Decoding circuit 8 Synthesis circuit

Claims (3)

[Claims] Claim 1: Extracting means for extracting line drawings based on gradation information of an input image; encoding means for encoding the line drawings extracted by the extraction means; and data encoded by the encoding means. An image encoding device comprising: multiplexing means for multiplexing tone information according to the tone information of the extracted line drawing. 2. The method further comprises replacement means for replacing the gradation information of the line drawing extracted by the extraction means with a predetermined value, and encoding means for encoding the information from the replacement means. The image encoding device according to claim 1. 3. The multiplexing means has a detection means for detecting a change in gradation information, and a table for registering the gradation information detected by the detection means, and the multiplexing means includes a detection means for detecting a change in gradation information, and a table for registering the gradation information detected by the detection means. 2. The image encoding apparatus according to claim 1, wherein the gradation information registered in the image encoding apparatus is multiplexed.