Image encoding apparatus, image decoding apparatus, and control methods therefor

An image decoding apparatus for decoding encoded image data, comprising:

• a decoding unit configured to generate quantized coefficient data of a plurality of sub-bands of up to decomposition level n (n≧2) by decoding the encoded image data;
• an inverse quantizing unit configured to inversely quantize the quantized coefficient data, obtained by decoding, in the sub-bands of the respective decomposition levels;
• and
• a transforming unit configured to generate image data by performing inverse discrete wavelet transform for the coefficient data, obtained by the inverse quantizing unit, in the sub-bands of the respective decomposition levels,
• wherein the inverse quantizing unit
• inversely quantizes each sub-band of decomposition level n based on a quantization parameter set for each sub-band, and
• inversely quantizes each sub-band of decomposition level n−1 or less based on a quantization parameter set for each sub-band and a weighting coefficient dependent on inversely quantized coefficient data of a sub-band LL of decomposition level n.

A control method for an image encoding apparatus which encodes image data, comprising:

• performing discrete wavelet transform for image data to be encoded up to decomposition level 2 or more to generate a plurality of sub-bands;
• quantizing coefficient data in the sub-bands obtained in the performing the discrete wavelet transform;
• and
• encoding the coefficient data quantized in the quantizing,
• wherein in the quantizing, the sub-bands of a lower decomposition level are quantized based on the coefficient data of the low-frequency sub-band of a highest decomposition level.

A control method for an image decoding apparatus which decodes encoded image data, comprising:

• generating quantized coefficient data of a plurality of sub-bands of up to decomposition level n (n≧2) by decoding the encoded image data;
• inversely quantizing the quantized coefficient data, obtained by decoding, in the sub-bands of the respective decomposition levels;
• and
• generating image data by performing inverse discrete wavelet transform for the coefficient data, obtained in the inversely quantizing, in the sub-bands of the respective decomposition levels,
• wherein in the inversely quantizing,
• each sub-band of decomposition level n is inversely quantized based on a quantization parameter set for each sub-band, and
• each sub-band of decomposition level n−1 or less is inversely quantized based on a quantization parameter set for each sub-band and a weighting coefficient dependent on inversely quantized coefficient data of a sub-band LL of decomposition level n.

A non-transitory computer-readable storage medium storing a program which causes an information processing apparatus to execute steps of a method for controlling the information processing apparatus which encodes image data, the method comprising:

• performing discrete wavelet transform for image data to be encoded up to decomposition level 2 or more to generate a plurality of sub-bands;
• quantizing coefficient data in the sub-bands obtained in the performing the discrete wavelet transform;
• and
• encoding the coefficient data quantized in the quantizing,
• wherein in the quantizing, the sub-bands of a lower decomposition level are quantized based on the coefficient data of the low-frequency sub-band of a highest decomposition level.

A non-transitory computer-readable storage medium storing a program which causes an information processing apparatus to execute steps of a method for controlling the information processing apparatus which decodes encoded image data, the method comprising:

• generating quantized coefficient data of a plurality of sub-bands of up to decomposition level n (n≧2) by decoding the encoded image data;
• inversely quantizing the quantized coefficient data, obtained by decoding, in the sub-bands of the respective decomposition levels;
• and
• generating image data by performing inverse discrete wavelet transform for the coefficient data, obtained in the inversely quantizing, in the sub-bands of the respective decomposition levels,
• wherein in the inversely quantizing,
• each sub-band of decomposition level n is inversely quantized based on a quantization parameter set for each sub-band, and
• each sub-band of decomposition level n−1 or less is inversely quantized based on a quantization parameter set for each sub-band and a weighting coefficient dependent on inversely quantized coefficient data of a sub-band LL of decomposition level n.