Image processing apparatus and method

• US 6,285,458 B1
• Filed: 07/30/1997
• Issued: 09/04/2001
• Est. Priority Date: 07/31/1996
• Status: Expired due to Fees

• Current Assignee: Fuji Xerox Company Limited (Xerox Holdings Corp.)
• Original Assignee: Fuji Xerox Company Limited (Xerox Holdings Corp.)
• Inventors: Yada, Shinichi
• Primary Examiner(s): Popovici, Dov
• Application Number:
  US08/903,381
• Time in Patent Office: 1,497 Days
• Field of Search: 395/114, 395/112, 395/115, 395/116, 395/101, 358/426, 358/261.1, 358/261.2, 358/261.3, 358/261.4, 382/239, 382/176, 382/180, 341/51, 341/95, 341/63, 341/107
• US Class Current: 358/1.15
• CPC Class Codes: H04N 1/41 Bandwidth or redundancy reduction by scanning H04N1/17 ; methods or arrangements for coding, decoding, compressing or decompressing digital video signals H04N19/00
• CPC Class Codes: H04N 19/115 Selection of the code volume for a coding unit prior to coding
• CPC Class Codes: H04N 19/12 Selection from among a plurality of transforms or standards, e.g. selection between discrete cosine transform [DCT] and sub-band transform or selection between H.263 and H.264
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/149 by estimating the code amount by means of a model, e.g. mathematical model or statistical model
• CPC Class Codes: H04N 19/15 by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
• CPC Class Codes: H04N 19/152 by measuring the fullness of the transmission buffer
• CPC Class Codes: H04N 19/17 the unit being an image region, e.g. an object
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/192 the adaptation method, adaptation tool or adaptation type being iterative or recursive
• CPC Class Codes: H04N 19/60 using transform coding
• CPC Class Codes: H04N 19/70 characterised by syntax aspects related to video coding, e.g. related to compression standards
• CPC Class Codes: H04N 19/93 Run-length coding
• CPC Class Codes: H04N 19/98 Adaptive-dynamic-range coding [ADRC]

Abstract

An image process apparatus, for use with image data combining areas of different image characteristics such as text and photos, which achieves a predetermined target compression rate and simultaneously minimizes quality deterioration after decompression, is described. The image analysis circuit analyzes the composition of the entire image data and calculates the optimum compression parameter. The compression process is performed using a selected compression method for each predetermined block. At the time of compression, the value of the parameter is used in order to select an appropriate compression method by switching compression methods among a plurality of compression methods for each block unit. Using optimum compression minimizes the amount of memory required to store the information.

Claims

1. An image processing apparatus, comprising:

an image input apparatus to input image data related to an image composed of image portions having different image characteristics;

an image data analyzer to analyze the image data in terms of pixel block units to discern the image portions having different image characteristics in the image, and the proportion of such portions with different image characteristics in the image;

an image data compression apparatus having a plurality of different image compression methods; and

a compression mode selector to select, for each pixel block unite an image data compression method from the plurality of different image compression methods based on a determination of the proportional amounts of such image portions having different image characteristics in the image.

2. The image processing apparatus of claim 1, further comprising:

a preset target encoded amount, the target encoded amount resulting from a target compression rate of the image data to be compressed;

a compressed image encoding data output apparatus to output encoded data of the compressed image, the encoded data including a resultant compression rate obtained by the image data compression apparatus;

an encoded amount monitor to monitor the encoded data output by the compressed image encoding data output apparatus; and

an encoded amount comparator to compare the encoded data in the encoded amount monitor with the target encoded amount.

3. The image processing apparatus of claim 2, wherein the compression apparatus is re-selected when the results of a comparison by the encoded amount monitor indicates that the encoded data exceeds the target encoded amount and the results of an analysis by the analyzer.

4. The image processing apparatus of claim 1, wherein said analyzer calculates the proportion of the image portions in the image using the image characteristics of the image portions.

5. The image processing apparatus of claim 1, wherein the image data includes code image data using page descriptive language and wherein the image processing apparatus further comprises:

a rasterizer to interpret the page descriptive language and render the code image data into raster data; and

discernment apparatus for discernment of image attributes of the code image data.

6. The image processing apparatus of claim 1, wherein the image portions include at least one of a background portion, a character or drawing portion, a computer graphics portion, and a scanned image portion.

7. The image processing apparatus of claim 1, wherein the proportion of such image portions is based on image characteristics of at least one of a background image portion, a character or drawing image portion, a computer graphics image portion, and a scanned image portion.

8. The image processing apparatus of claim 1, wherein the proportion of such image portions is determined based on one of the minimum and maximum values of the coordinates for each of the one or more image portions, a count of a number of pixels in each of the one or more image portions, and a count of a number of blocks of a predetermined size in each of the one or more image portions.

9. The image processing apparatus of claim 1, wherein the analyzer determines at least one threshold value from the determined proportion, the selector compares the at least one threshold to a color count of the number of pixel colors in a first image portion, and the selector selects the image data compression method based on the comparison of the at least one threshold to the color count.

10. The image processing apparatus of claim 1, wherein the plurality of different image compression methods includes at least one of a block single-color approximation compression method, a block run-length compression method, a block-internal two-color approximation compression method, an adaptive discrete cosine transform compression method, and a block-internal four-color approximation compression method.

11. The image processing apparatus of claim 1, wherein the selected image data compression method compresses a first image portion into blocks of compressed image data and a tag signal is added to each block, the tag signal identifying the selected image data compression method.

12. An image processing method, comprising:

receiving and converting digital data for an image composed of portions having different image characteristics;

analyzing the digital image data in terms of pixel block units to discern the portions having different image characteristics in the image, and the proportion of such portions of different image characteristic in the image; and

selecting, for each pixel block unit, an image data compression method from a plurality of different image data compression methods based on a determination of the proportional amounts of such portions having different image characteristics in the image.

13. The method of claim 12, further comprising:

determining a target encoded amount resulting from a target compression rate of the image data;

outputting encoded data of an image portion, the encoded data including a resultant compression rate obtained by the selected image data compression method; and

comparing the encoded data with the target encoded amount.

14. The method of claim 13, further comprising selecting a different image data compression method if the results of the comparing step indicate that the encoded data exceeds the target encoded amount.

15. The method of claim 12, wherein the proportion is based on characteristics of at least one of a background image portion, a character or drawing image portion, a computer graphics image portion, and a scanned image portion.

16. The method of claim 15, wherein the proportion is determined based on one of the minimum and maximum values of the coordinates for each of one or more image portions, a count of a number of pixels in each of the one or more image portions, and a count of a number of blocks of a predetermined size in each of the one or more image portions.

17. The method of claim 12, further comprising:

determining at least one threshold value from the determined proportion; and

comparing the at least one threshold value to a color count of the number of pixel colors in an image portion, wherein the selection of a selected image data compression method is based on the comparison of the at least one threshold value to the color count.

18. The method of claim 12, further comprising:

compressing an image portion into blocks of compressed image data using the selected image data compression method; and

adding a tag signal to each block of the compressed image data, the tag signal identifying the selected image data compression method.