JP2006005478A5

JP2006005478A5 -

Info

Publication number: JP2006005478A5
Application number: JP2004177346A
Authority: JP
Filing date: 2004-06-15
Publication date: 2007-07-19
Anticipated expiration: 2024-06-15

Claims

An image decoding device having a function of decoding extended JPEG encoded data,
Determining means for determining whether the encoded data is baseline JPEG encoded data or extended JPEG encoded data by analyzing header information of the encoded data;
Decoding means for decoding the encoded data;
When the determination means determines that the encoded data is baseline JPEG encoded data, the decoding value decoded by the decoding means is D, and the quantization step of quantization table information included in the header of the encoded data When the value is Q and the inverse quantized data is X,
X = D × Q × 2 ⁿ
(N is an integer from 1 to 4)
Calculating means for calculating the dequantized data X as:
An inverse DCT transforming means for inverse DCT transforming the inversely quantized data X obtained by the calculating means;
When the determination unit determines that the input encoded data is baseline JPEG encoded data, the image data after the inverse DCT conversion is rounded and output, and the encoded data input by the determination unit is An image decoding apparatus comprising: output means for outputting the image data after the inverse DCT conversion as a decoding result when it is determined that the data is extended JPEG encoded data.

The image data obtained by the inverse DCT conversion means is luminance and color difference components, and further comprises color conversion means for converting the luminance and color difference components into color components constituting a color image. Item 2. The image decoding device according to Item 1.

The calculating means includes
When the determination means determines that the encoded data is baseline JPEG encoded data, the result obtained by multiplying the quantization step value Q of the quantization table information stored in the header of the encoded data by 2 ⁿ is obtained. And holding means for holding the quantization step value Q of the quantization table information stored in the header of the encoded data as it is when it is determined to be extended JPEG encoded data;
The computing means for computing inverse quantized data by multiplying the decoded step value D decoded by the decoding means by the quantization step value Q held by the holding means. Image decoding apparatus.

The calculating means includes
Holding means for holding the quantization step value Q of the quantization table information stored in the header of the encoded data;
First computing means for multiplying the decoded value decoded by the decoding means by the quantization step value Q held by the holding means;
When the determination unit determines that the encoded data is extended JPEG encoded data, the calculation result of the first calculation unit is output as the calculation result of the calculation unit, and is the baseline JPEG encoded data. And a second calculation means for multiplying the result obtained by the first calculation means by 2 ⁿ and outputting the result as the calculation result of the calculation means. The image decoding device described.

The calculating means includes
Holding means for holding the quantization step value Q of the quantization table information stored in the header of the encoded data;
When the determination unit determines that the encoded data is extended JPEG encoded data, the quantization step value Q held in the holding unit is output, and it is determined that the encoded data is baseline JPEG encoded data. In the case, the first calculation means for outputting the quantization step value Q held in the holding means multiplied by 2 ⁿ , and
The image decoding apparatus according to claim 1, further comprising: a second calculation unit that multiplies the output value of the first calculation unit by the decoded value decoded by the decoding unit.

An image encoding device for JPEG encoding image data composed of a plurality of components,
Determining means for determining whether each component of image data to be encoded is expressed in 12 bits;
A bit expansion unit that expands the number of bits by multiplying each component by ²ⁿ (where n is an integer of 1 to 4) when the determination unit determines that each component is image data represented by less than 12 bits; ,
Color conversion means for inputting image data in which each color component is expressed by 12 bits, or image data in which the number of bits of each component is extended by the bit extension means, and converting it into luminance and color difference components;
DCT conversion means for DCT converting each component value obtained by the color conversion means;
Baseline JPEG quantization table information and extended JPEG quantization table information can be output, and if the determination unit determines that each component of the image data to be encoded is expressed in 8 bits, the baseline When the quantization step value of the JPEG quantization table information is output by multiplying by 2 ⁿ and it is determined that each component of the image data to be encoded is represented by 12 bits, the quantization table for extended JPEG A quantization table output means for outputting a quantization step value of information;
Quantization means for quantizing the coefficient obtained by the conversion by the DCT conversion means based on the quantization step value output from the holding means;
Code string generation means for generating a code string from the quantized coefficients;
Baseline JPEG encoded data by storing information indicating the determination result of the determination unit and the used quantization table information in a predetermined area of the header, followed by the code string generated by the code string generation unit Or an encoding means for generating extended JPEG encoded data.

The image coding apparatus according to claim 6, wherein the bit expansion means expands the number of bits by multiplying each component by eight.

The image coding apparatus according to claim 6, wherein the bit expansion means expands the number of bits by multiplying each component by 16.

7. The image coding apparatus according to claim 6, wherein the color conversion means does not perform color conversion processing when image data before color conversion is composed of luminance and color difference components.