Image coding apparatus and method thereof
An image coding apparatus configured to support a coding scheme capable of selecting a size of a block to be coded from a plurality of sizes includes a quantization unit configured to assign a quantization step size to each block of an image to be coded and quantize each block, a coding unit configured to code image data relating to each block quantized by the quantization unit, a minimum quantization step value setting unit configured to set a minimum quantization step value according to the size of each block and apply the minimum quantization step value to each block of the image to be coded, and a quantization step determination unit configured to determine the quantization step size of each block not to fall below the minimum quantization step value thereof.
1. A coding apparatus comprising:
a transforming unit that transforms image data corresponding to a target block including in an image into transformed data, wherein a size of the target block is selected from different sizes;
a controlling unit that (a) determines a minimum value to be assigned to the target block in accordance with the size of the target block, (b) adjusts a quantization step size of the target block not to fall below the determined minimum value, and (c) adjusts a quantization step size of another block whose quantization step size exceeds a minimum value assigned to the another block to be closer to the minimum value assigned to the another block so that a code amount of the another block is increased;
a quantization unit that quantizes the transformed data using the adjusted quantization step size of the target block to generate quantized data; and
a coding unit that codes the quantized data.
2. The coding apparatus according to claim 1 , wherein the minimum value to be assigned to the target block is determined in accordance with the size of the target block and a target data rate.
3. The coding apparatus according to claim 1 , wherein the minimum value to be assigned to the target block is determined in accordance with the size of the target block and a feature of an image.
4. The coding apparatus according to claim 1 , wherein the minimum value to be assigned to the target block is determined in accordance with the size of the target block and information about a main object area.
5. The coding apparatus according to claim 1 , wherein the minimum value to be assigned to the target block is determined so that the minimum value to be assigned to the target block decreases as the size of the target block increases.
6. The coding apparatus according to claim 1 , wherein the minimum value to be assigned to the target block is determined so that the minimum value to be assigned to the target block increases as the size of the target block increases.
7. A method comprising:
transforming image data corresponding to a target block including in an image into transformed data, wherein a size of the target block is selected from different sizes;
determining a minimum value to be assigned to the target block in accordance with the size of the target block;
adjusting a quantization step size of the target block not to fall below the determined minimum value;
adjusting a quantization step size of another block whose quantization step size exceeds a minimum value assigned to the another block to be closer to the minimum value assigned to the another block so that a code amount of the another block is increased;
quantizing the transformed data using the adjusted quantization step size of the target block to generate quantized data; and
coding the quantized data.
8. The method according to claim 7 , wherein the minimum value to be assigned to the target block is determined in accordance with the size of the target block and a target data rate.
9. The method according to claim 7 , wherein the minimum value to be assigned to the target block is determined in accordance with the size of the target block and a feature of an image.
10. The method according to claim 7 , wherein the minimum value to be assigned to the target block is determined in accordance with the size of the target block and information about a main object area.
11. The method according to claim 7 , wherein the minimum value to be assigned to the target block is determined so that the minimum value to be assigned to the target block decreases as the size of the target block increases.
12. The method according to claim 7 , wherein the minimum value to be assigned to the target block is determined so that the minimum value to be assigned to the target block increases as the size of the target block increases.
13. A non-transitory computer-readable storage medium that stores a program for causing a computer to perform a method comprising:
transforming image data corresponding to a target block including in an image into transformed data, wherein a size of the target block is selected from different sizes;
determining a minimum value to be assigned to the target block in accordance with the size of the target block;
adjusting a quantization step size of the target block not to fall below the determined minimum value;
adjusting a quantization step size of another block whose quantization step size exceeds a minimum value assigned to the another block to be closer to the minimum value assigned to the another block so that a code amount of the another block is increased;
quantizing the transformed data using the adjusted quantization step size of the target block to generate quantized data; and
coding the quantized data.