Image displaying method including image encoding method and image decoding method

1. A method for displaying an image, the method comprising:

deriving a luminance prediction value based on a luminance value of previous image data, wherein the previous image data corresponds to a previous frame or a previously processed line of pixels for which an encoding operation is previously performed;

calculating a luminance residual by subtracting the luminance prediction value from a luminance value of current image data, wherein the current image data corresponds to a current frame or a currently processed line of pixels;

deriving a chrominance prediction value based on a chrominance value of the previous image data;

calculating a first chrominance residual by subtracting the chrominance prediction value from a chrominance value of the current image data;

deriving a quantized luminance value by quantizing the luminance residual;

deriving an inverse quantized luminance value by inverse quantizing the quantized luminance value;

selecting one of candidate coefficients as a modification factor;

calculating a second chrominance residual by subtracting an adjustment value from the first chrominance residual, wherein the adjustment value is equal to the inverse quantized luminance value multiplied by the modification factor;

deriving a quantized chrominance value by quantizing the second chrominance residual;

encoding the quantized luminance value and the quantized chrominance value to produce encoded data;

decoding the encoded data to obtain decoded image data, the decoded image data comprising decoded luminance data and decoded chrominance data; and

controlling a display device according to the decoded image data to display the image.

2. The method of claim 1 , wherein the candidate coefficients are greater than or equal to −1, less than or equal to 1, and equal to m/2 n , where n and m represent integers, and

wherein the modification factor is determined among the candidate coefficients such that a difference between the first chrominance residual and the adjustment value is minimized.

3. The method of claim 1 , comprising:

dividing the previous image data into previous sub-image data sets that correspond to sub-image of the image;

dividing the current image data into current sub-image data sets that correspond to the sub-image of the image;

determining sub-image quantized luminance values and sub-image quantized chrominance values using the previous sub-image data sets and the current sub-image data sets;

calculating compression difficulty values for the sub-images of the image based on an average quantized value of the previous sub-image data sets;

calculating compression difficulty ratios using the compression difficulty value and an average of the compression difficulty values; and

adjusting bit rates for the sub-images of the image based on the compression difficulty ratios.

4. The method of claim 3 , wherein the compression difficulty ratios are converted to m/2 n , where n and m represent integers.

5. The method of claim 1 , wherein the deriving the luminance prediction value includes:

selecting one of candidate vector values as a first vector value such that a first similarity index between a luminance value corresponding to the first vector value and a luminance value corresponding to a reference position is minimized;

selecting one of the first vector value and adjacent vector values adjacent to the first vector value as a second vector value such that a second similarity index between a luminance value corresponding to the second vector value and the luminance value corresponding to the reference position is minimized; and

calculating the luminance prediction value based on the luminance value corresponding to the second vector value.

6. The method of claim 5 , wherein intervals between immediately neighboring vector values of the candidate vector values are integers greater than 1.

7. The method of claim 5 , wherein intervals between immediately neighboring vector values of the candidate vector values increase as distances between the reference position and the candidate vector values increase.

8. The method of claim 5 , wherein at least one of the first similarity index and the second similarity index is calculated using a sum of absolute differences between one or more pixel values of pixels that are included in a pixel group or adjacent to the pixel group and one or more pixel values of pixels located in the reference position.

9. The method of claim 1 , wherein the deriving the luminance prediction value includes:

calculating median values of luminance values of pixels that are adjacent to each other;

selecting one of candidate vector values corresponding the median values as a first vector value such that a similarity index between a median value of the first vector value and a luminance value corresponding to a reference position is minimized, intervals between immediately neighboring vector values of the candidate vector values are integers greater than 1;

selecting one of the first vector value and adjacent vector values adjacent to the first vector value as a second vector value such that a similarity index between a luminance value corresponding to the second vector value and the luminance value corresponding to the reference position is minimized; and

calculating the luminance prediction value based on the luminance value corresponding to the second vector value.

10. The method of claim 1 , wherein a first luminance prediction value and a first chrominance prediction value associated with a first pixel located at a boundary of a pixel group are adjusted based on a second luminance prediction value and a second chrominance prediction value associated with a second pixel adjacent to the first pixel and outside the pixel group.

11. The method of claim 1 , wherein the deriving the quantized chrominance value includes:

selecting one of candidate quantization tables as a quantization table based on a difference value between an absolute average of luminance residuals and an absolute average of chrominance residuals;

deriving a chrominance quantization parameter from the quantization table; and

quantizing the second chrominance residual based on the chrominance quantization parameter.

12. The method of claim 1 , wherein the deriving the quantized luminance value includes:

deriving a luminance quantization parameter from a quantization table;

subtracting an offset value from the luminance quantization parameter to produce an adjusted luminance quantization parameter when a pixel is located at a boundary of a pixel group; and

quantizing a first luminance residual for the pixel based on the adjusted luminance quantization parameter.

13. The method of claim 12 , wherein the offset value increases as the luminance quantization parameter increases.

14. A method for displaying an image, the method comprising:

deriving a luminance prediction value for a first pixel based on a luminance value of previous image data, wherein the first pixel is located at a boundary of a pixel group;

calculating a luminance residual for the first pixel by subtracting the luminance prediction value from a luminance value of current image data;

deriving a chrominance prediction value for the first pixel based on a chrominance value of the previous image data;

calculating a chrominance residual for the first pixel by subtracting the chrominance prediction value from a chrominance value of the current image data;

deriving a quantization parameter from a quantization table;

subtracting an offset value from the quantization parameter to produce an adjusted quantization parameter;

quantizing the luminance residual and the chrominance residual for the pixel based on the adjusted quantization parameter to derive a quantized luminance value and a quantized chrominance value;

encoding the quantized luminance value and the quantized chrominance value to produce encoded data;

decoding the encoded data to obtain decoded image data; and

controlling a display device according to the decoded image data to display the image.

15. The method of claim 14 , wherein the offset value increases as the quantization parameter increases.

16. The method of claim 14 , wherein the quantization table is determined among a plurality of candidate quantization tables based on a difference value between an absolute average of luminance residuals and an absolute average of chrominance residuals.

17. A method for displaying an image, the method comprising:

selecting one of candidate vector values as a first vector value such that a first similarity index between a pixel value corresponding to the first vector value and a pixel value corresponding to a reference position is minimized, wherein intervals between immediately neighboring vector values of the candidate vector values are integers greater than 1;

selecting one of the first vector value and adjacent vector values adjacent to the first vector value as a second vector value such that a second similarity index between a pixel value corresponding to the second vector value and the pixel value corresponding to the reference position is minimized;

calculating a luminance prediction value and a chrominance prediction value based on the pixel value corresponding to the second vector value;

calculating a luminance residual by subtracting the luminance prediction value from a luminance value of current image data;

calculating a chrominance residual by subtracting the chrominance prediction value from a chrominance value of the current image data;

quantizing the luminance residual and the chrominance residual to derive a quantized luminance value and a quantized chrominance value;

encoding the quantized luminance value and the quantized chrominance value to produce encoded data;

decoding the encoded data to obtain decoded image data; and

controlling a display device according to the decoded image data to display the image.

18. The method of claim 17 , wherein at least one of the first similarity index and the second similarity index is calculated using a sum of absolute differences between one or more pixel values of pixels that are included in a pixel group or adjacent to the pixel group and one or more pixel values of pixels located in the reference position.

19. The method of claim 17 , wherein a first luminance prediction value and a first chrominance prediction value associated with a first pixel located at a boundary of a pixel group are adjusted based on a second luminance prediction value and a second chrominance prediction value associated with a second pixel adjacent to the first pixel and outside the pixel group.

20. A method for displaying an image, the method comprising:

deriving a quantized luminance value and a quantized chrominance value by decoding a bitstream;

deriving an inverse quantized luminance value by inverse quantizing the quantized luminance value;

deriving a luminance prediction value based on a luminance value of previous image data, wherein the previous image data corresponds to a previous frame or a previously processed line of pixels for which an encoding operation is previously performed;

generating a decoded luminance value by adding the inverse quantized luminance value and the luminance prediction value;

deriving an inverse quantized chrominance value by inverse quantizing the quantized chrominance value;

deriving a chrominance prediction value based on a chrominance value of the previous image data;

generating a first decoded chrominance value by adding the inverse quantized chrominance value and the chrominance prediction value;

selecting one of candidate coefficients as a modification factor;

generating a second decoded chrominance value by adding the first decoded chrominance value and an addition value, the addition value being equal to the inverse quantized luminance value multiplied by the modification factor; and

controlling a display device according to at least one of the first decoded chrominance value and the second decoded chrominance value to display the image.