Image encoding apparatus and image encoding method

An image processing apparatus comprising:

• one or more processors;
• and a memory storing a computer program comprising instructions, when executed by the one or more processors, cause the one or more processors to function as:
• an acquisition unit configured to input image data, and to output image data of blocks comprising a plurality of groups each including a predetermined number of pixels, wherein the acquisition unit changes an order of the image data from an order of the inputted image data, so that arrangements of pixels between adjacent blocks are in reverse order of each other;
• a deciding unit configured to decide, for each of the groups, a quantization parameter, that is used for quantization of image data of the group, and an encoding scheme such that a code length of the blocks, which are encoding target blocks, does not exceed a predetermined value;
• and
• an encoding unit configured to, in accordance with the quantization parameter and encoding scheme decided for each group by the deciding unit, encode the image data of the encoding target blocks output from the acquisition unit to generate encoded data,
• wherein the encoding unit encodes the image data using a first encoding scheme for outputting quantized image data and a second encoding scheme for outputting encoded data of a differential between quantized image data and predicted data, and
• wherein the deciding unit decides as the encoding scheme of the group whichever of the first encoding scheme and the second encoding scheme can achieve a smaller code length, and
• wherein the deciding unit, among a plurality of quantization parameters, decides as the quantization parameter of the group either a first quantization parameter, or a second quantization parameter corresponding to a smaller quantization step than the quantization step corresponding to the first quantization parameter, and
• wherein the deciding unit, so that the code length of the encoded data of the encoding target blocks, which are generated by quantizing all of the groups of the encoding target blocks using the first quantization parameter and encoding the respective groups using the decided encoding schemes, does not exceed the predetermined value and is a maximum value, decides one of the plurality of quantization parameters as the first quantization parameter, and decides the second quantization parameter as the quantization parameter for some of the groups of the encoding target blocks.