Processing of images using a limited number of bits

• US RE43,256 E1
• Filed: 07/11/2011
• Issued: 03/20/2012
• Est. Priority Date: 01/13/2003
• Status: Active Grant

• Current Assignee: Nokia Corporation
• Original Assignee: Nokia Corporation
• Inventors: Kalevo, Ossi
• Primary Examiner(s): Tucker, Wesley
• Assistant Examiner(s): WOLDEMARIAM, AKLILU K
• Application Number:
  US13/135,639
• Time in Patent Office: 253 Days
• Field of Search: 382/100, 382/232, 382/224, 382/238, 702/3, 704/217
• US Class Current: 382/238
• CPC Class Codes: H04N 19/184 the unit being bits, e.g. of the compressed video stream
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/50 using predictive coding H04N19/61 takes precedence
• CPC Class Codes: H04N 19/98 Adaptive-dynamic-range coding [ADRC]

Abstract

The invention relates to a method as well as a system, a device, an encoder and a decoder, and a computer software product for image processing by the method. In the invention, the number of bits is limited in the bit string of a pixel to be processed, wherein the pixel is encoded with the limited number of bits. A prediction value corresponding to said pixel is searched for. If it is found, the difference between the pixel and the prediction value is determined, to select the method for encoding the bit string of said pixel. Also, a code word is encoded in the bit string, to indicate the selected encoding method. If the prediction value is missing, the number of bits in said pixel is limited by quantizing. By means of the invention, a fixed number of bits is obtained for all encoded pixels in an image.

Claims

1. A method for image processing, in which the number of bits is fixed in an encoded bit string, wherein a pixel is encoded into the bit string, the method comprising:

if a prediction value is not available for the pixel, encoding a quantized pixel value to the bit string,

if the prediction value is available for the pixel,

determining a difference between the pixel value and the prediction value, which difference is used for selecting a method for encoding among more than two encoding methods to encode said pixel into the bit string, each method for encoding having a certain step size for quantizing a value, and said certain step size being different in each method for encoding, wherein the method further comprising;

determining a code word indicating the selected encoding method on the basis of the original and limited number of bits in the pixel in such a way that the code word length does not exceed N−

(M−

1) where M corresponds to the limited number of bits and N corresponds to the original number of bits;

encoding said code word indicating the selected encoding method and the quantizer step size, and the quantized value to the bit string,

in which method the encoded bit string has a fixed-length smaller than the length of the originally digitized pixel for each encoded pixels in the image bit string before encoding.

2. The method according to claim 1, wherein the code word to indicate the selected encoding method is of variable length.

3. The method according to claim 1, wherein quantizing is used to encode the bit string, wherein first a limit value is determined, wherein said difference is compared with said limit value in such a way that when the difference is smaller, the quantized value is determined by quantizing the difference, whereas when the difference is greater, the quantized value is determined by quantizing the original digitized value of the pixel.

4. The method according to claim 1, wherein said code word is determined on the basis of the original and limited number of bits in the pixel in such a way that the code word length is two bits when the absolute value of the difference is less than 32, and that the code word length is three bits when the absolute value of the difference is more than 31 and less than 128, wherein when the absolute value of the difference exceeds 128, the code word length is selected to be one bit, wherein the encoding method is changed.

5. The method according to claim 1, wherein the encoding method to be used is selected between differential pulse code modulation and pulse code modulation coding in such a way that code word lengths greater than one bit indicate the use of differential pulse code modulation coding, wherein the code word length of one bit indicates the use of pulse code modulation coding.

6. The method according to claim 1, wherein the encoding method to be used is selected between ordinary differential pulse code modulation coding and smart differential pulse code modulation coding in such a way that code word lengths greater than one bit indicate the use of differential pulse code modulation coding, wherein the code word length of one bit indicates the use of smart differential pulse code modulation coding.

7. The method according to claim 1, wherein said prediction value is the value of one encoded pixel value or the average of several encoded pixel values.

8. The method according to claim 1, wherein the pixel is encoded for transfer between a camera module and an electronic device.

23. A computer readable medium for storing software instructions for image processing with a limited number of bits in an encoded bit string of a pixel, as well as for encoding the pixel to the limited number of bits where said software instructions are executed by a processor to carry out the method of claim 1.

9. An image processing system comprising a device comprising a processor configured to process an image, wherein the device comprises means for encoding a pixel to an encoded bit string, in which the number of bits is fixed, wherein:

if a prediction value is not available for the pixel, the means for encoding is configured to encode a quantized pixel value to the bit string,

if the prediction value is available, the device is configured to determine a difference between the pixel value and the prediction value, which difference is used for selecting a method for encoding among more than two encoding methods to encode said pixel into the bit string, each method for encoding having a certain step size for quantizing a value, and said certain step size being different in each method for encoding a code word indicating the selected encoding method on the basis of the original and limited number of bits in the pixel in such a way that the code word length does not exceed N−

(M−

1) where M corresponds to the limited number of bits and N corresponds to the original number of bits, and,

to encode a code word indicating the selected encoding method and the quantizer step size, and the quantized value to the bit string, in which device the encoded bit string has fixed-length smaller than the length of the originally digitized pixel for each encoded pixel in the image bit string before encoding.

10. The system according to claim 9, wherein the system is also configured to determine a limit value, wherein the system is also arranged to compare said difference with said limit value in such a way that when the difference is smaller, the system is arranged to determine the quantized value by quantizing the difference, whereas when the difference is greater, the system is arranged to determine the quantized value by quantizing the original digitized value of the pixel.

11. The system according to claim 9, wherein the system is also configured for forming the length of the code word on the basis of the original and limited number of bits in the pixel in such a way that the code word length is two bits when the absolute value of the difference is less than 32, and that the code word length is three bits when the absolute value of the difference is more than 31 and less than 128, wherein when the absolute value of the difference exceeds 128, the code word length is one bit, to change the encoding method.

12. The system according to claim 9, wherein the system also comprises a differential pulse code modulation codec and a pulse code modulation codec, wherein code word lengths greater than one bit indicate the use of the differential pulse code modulation codec, wherein the code word length of one bit indicates the use of the pulse code modulation codec.

13. The system according to claim 9, wherein the system also comprises an ordinary differential pulse code modulation codec and a smart differential pulse code modulation codec, wherein code word lengths greater than one bit indicate the use of the differential pulse code modulation codec, wherein the code word length of one bit indicates the use of the smart differential pulse code modulation codec.

14. The system according to claim 9, wherein said prediction value is the value of one encoded pixel value or the average of several encoded pixel values.

15. The system according to claim 9, wherein the system also comprises means for decoding the bit string to correspond to the encoding.

16. The system according to claim 9, wherein the system also comprises a camera module and an electronic device.

17. The system according to claim 16, wherein the electronic device comprises means for performing mobile communication.

18. A device for image processing, which device comprises a processor configured to process an image, wherein the device comprises means for encoding a pixel to an encoded bit string, in which the number of bits is fixed, wherein:

if a prediction value is not available for the pixel;

the means for encoding is configured to encode a quantized pixel value to the bit string

if the prediction value is available, the means for encoding is configured

to determine the difference between the pixel value and the prediction value, which difference is used for selecting a method for encoding among more than two encoding methods to encode said pixel into the bit string, each method for encoding having a certain step size for quantizing a value, and to determine a code word indicating the selected encoding method on the basis of the original and limited number of bits in the pixel in such a way that the code word length does not exceed N−

(M−

1) where M corresponds to the limited number of bits and N corresponds to the original number of bits, and,

to encode said code word indicating the selected encoding method and the quantizer step size, and the quantized value to the bit string,

in which device the encoded bit string has fixed-length smaller than the length of the originally digitized pixel for each encoded pixel in the image bit string before encoding.

19. The device according to claim 18, wherein the device is also configured for determining a limit value, wherein the device is also arranged to compare said difference with said limit value in such a way that when the difference is smaller, the device is arranged to determine a quantized value by quantizing the difference, whereas when the difference is greater, the device is arranged to determine the quantized value by quantizing the original digitized value of the pixel.

20. The device according to claim 18, wherein the device comprises also a decoder for decoding the bit string in the way indicated by the code word.

21. The device according to claim 18, wherein the device also comprises a transceiver for performing mobile communication.

22. The device according to claim 18, wherein the device also comprises a transceiver for performing mobile communication.

24. A camera module comprising the device of claim 18.

25. A circuit for image processing, which circuit comprises an encoder and a decoder, which encoder comprises encoding means configured to encode a pixel to an encoded bit string, in which the number of bits is fixed, wherein:

if a prediction value is not available for the pixel, the encoding means is configured to encode a quantized pixel value to the bit string,

if the prediction value is available, the encoding means is configured to determine

a difference between the pixel value and the prediction value, which difference is used for selecting a method for encoding among more than two encoding methods to encode said pixel into the bit string, each method for encoding having a certain step size for quantizing a value, and said certain step size being different in each method for encoding determine a code word indicating the selected encoding method on the basis of the original and limited number of bits in the pixel in such a way that the code word length does not exceed N−

(M−

1) where M corresponds to the limited number of bits and N corresponds to the original number of bits, and,

to encode said code word indicating the selected encoding method and quantizer step sizes and the quantizer value to the bit string,

in which the circuit the encoded bit string has fixed-length smaller than the length of the originally digitized pixel for each encoded pixel in the image bit string before encoding.

26. The circuit according to claim 25, wherein the encoding method to be used is differential pulse code modulation or pulse code modulation coding.

27. The circuit according to claim 25, wherein the encoding method to be used is ordinary differential pulse code modulation coding or smart differential pulse code modulation coding.

28. The circuit according to claim 25, wherein the decoder is arranged to decode the bit string by a decoding method corresponding to the encoding method used.

29. A device for image processing, comprising:

a decoder for decoding an encoded bit string to obtain pixels of an image, in which bit string the number of bits is fixed,

wherein the bit string comprises a code word and a value, wherein the decoder comprises decoding means configured

to recognize the code word to select a decoding method indicated by the code word among at least a first decoding method and a second decoding method corresponding with the encoding method used in forming the bit string;

to determine a dequantizer value on the bases of the selected decoding method,

wherein the decoder comprises a memory for storing at least one decoded pixel as a prediction value, wherein the device is arranged to retrieve the prediction value corresponding to the pixel from said memory,

wherein said code word has been determined on the basis of the original and the limited number of bits in the pixel in such a way that the code word length does not exceed N−

(M−

1) where M corresponds to the limited number of bits and N corresponds to the original number of bits,

wherein said device is configured to dequantize said value by said dequantizer value to obtain a dequantized value, and

if the first decoding method was selected, the device is configured to use said dequantized value to obtain the pixel value,

if the second decoding method was selected, the device is configured to use said dequantized value and said prediction value to obtain the pixel value,

in which device the encoded bit string has fixed-length smaller than the length of the obtained pixel value for each pixel in the image bit string before encoding.

30. A device for image processing, which device comprises a processor configured to process an image, wherein the device comprises encoding means for encoding a pixel to an encoded bit string, in which the number of bits is fixed, wherein

if a prediction value is not available for the pixel:

the encoding means is configured to encode a quantized pixel value to the bit string, if the prediction value is available, wherein the encoding means is configured

to determine the difference between the pixel value and the prediction value, which difference is used for selecting a method for encoding among more than two encoding methods to encode said pixel into the bit string, each method for encoding having a certain step size for quantizing a value, and said certain step size being different in each method for encoding to determine a code word indicating the selected encoding method on the basis of the original and limited number of bits in the pixel in such a way that the code word length does not exceed N−

(M−

1) where M corresponds to the limited number of bits and N corresponds to the original number of bits, and,

to encode the code word indicating the selected encoding method and the quantizer step sizes and the quantized value to the bit string;

in which device the encoded bit string has fixed-length smaller than the length of the originally digitized pixel for each encoded pixel in the image bit string before encoding.