Amount-of-compressed data control method and image data compressing apparatus

A method for compressing image data, comprising:

• quantizing image data corresponding to at least one digital image, the quantizing comprising:
• dividing the image data into a plurality of data blocks, the data blocks comprising corresponding numbers of pixels;
• applying orthogonal transformations to the data blocks, the orthogonal transformations generating corresponding conversion coefficients for the pixels of the data blocks;
• computing scaled threshold values associated with a quantization matrix;
• and
• calculating quotients of the conversion coefficients and corresponding ones of the scaled threshold values to generate quantized image data;
• and
• compressing the quantized data in accordance with a variable-length encoding scheme, wherein:
• the scaled threshold values enable compressed data to fit within a predetermined range of a target amount of data;
• and
• the computing comprises:
• determining an initial scale factor for the threshold values, based on the target data amount;
• calculating a corrected scale factor based on the initial scale factor and a correction coefficient;
• and
• computing the scaled threshold values, based on at least corrected scale factor.

A method for compressing image data, comprising:

• quantizing image data corresponding to at least one digital image, the quantizing comprising:
• dividing the image data into a plurality of data blocks, the data blocks comprising corresponding numbers of pixels;
• applying orthogonal transform on each block transformations to the data blocks, the orthogonal transformations generating corresponding conversion coefficients for the pixels of the data blocks;
• computing scaled threshold values associated with a quantization matrix, based on a first scale factor;
• and
• calculating quotients of the conversion coefficients and corresponding ones of the scaled threshold values to generate quantized image data;
• compressing the quantized data in accordance with a variable-length encoding scheme;
• determining whether an amount of the compressed data falls within a target amount of data;
• and
• determining, when the compressed data amount fails to fall within the target amount, a second scale factor for the threshold values of the quantization matrix, the determining comprising:
• computing a provisional scale factor for the threshold values of the quantization matrix, based on the target amount of data;
• and
• calculating the second scale factor based, on an application of an attenuation factor to at least one of the provisional scale factor or the first scale factor,
• wherein the second scale factor enables the amount of compressed data to fit within the target amount of data.

An image data compressing apparatus comprising:

• a quantization section for quantizing image data corresponding to at least one digital image, the quantization section being configured to:
• divide the image data into a plurality of data blocks, the data blocks comprising corresponding numbers of pixels;
• applying orthogonal transformations to the data blocks, the orthogonal transformations generating corresponding conversion coefficients for the pixels of the data blocks;
• computing scaled threshold values associated with a quantization matrix, based on at least one scale factor and a corresponding scaling interval;
• and
• calculating quotients of the conversion coefficients and corresponding ones of the scaled threshold values to generate quantized image data;
• and
• an image data compressing section for compressing the quantized data, wherein:
• the at least one scale factor and the scaling interval enable the compressed data to fit within a predetermined range of a target amount of data;
• and
• the quantization section is further configured to:
• partition the scaling interval into a plurality of sub-intervals;
• calculate estimated values of the at least one scale factor for the sub-intervals, based on a relationship between the at least one scale factor and an amount of the compressed data;
• and
• compute the scaled threshold values, based on at least the estimated scale factor values.

An image data compressing apparatus, comprising:

• a quantization section for quantizing image data corresponding to at least one digital image, the quantization section being configured to:
• divide the image data into a plurality of data blocks, the data blocks comprising corresponding numbers of pixels;
• apply orthogonal transformations to the data blocks, the orthogonal transformations generating corresponding conversion coefficients for the pixels of the data blocks;
• compute scaled threshold values associated with a quantization matrix;
• and
• calculate quotients of the conversion coefficients and corresponding ones of the scaled threshold values to generate quantized image data;
• and
• an image data compressing section for compressing the quantized data, wherein:
• the scaled threshold values enable compressed data to fit within a predetermined range of a target amount of data;
• and
• the quantization section is further configured to:
• determine an initial scale factor for the threshold values, based on the target data amount;
• calculate a corrected scale factor based on the initial scale factor and a correction coefficient;
• and
• compute the scaled threshold values, based on at least corrected scale factor.

An image data compressing apparatus comprising:

• a quantization section for quantizing image data corresponding to at least one digital image, the quantization section being configured to:
• divide the image data into a plurality of data blocks, the data blocks comprising corresponding numbers of pixels;
• apply orthogonal transformations to the data blocks, the orthogonal transformations generating corresponding conversion coefficients for the pixels of the data blocks;
• compute scaled threshold values associated with a quantization matrix, based on a first scale factor;
• and
• calculate quotients of the conversion coefficients and corresponding ones of the scaled threshold values to generate quantized image data;
• an image data compressing section for compressing the quantized data in accordance with a variable-length encoding scheme;
• and
• a determination section for:
• determining whether an amount of the compressed data falls within a target amount of data;
• computing a provisional scale factor for the threshold values of the quantization matrix, based on the target amount of data, when the compressed data amount fails to fall within the target data amount;
• and
• determining the second scale factor for the threshold value of the quantization matrix, based on an application of an attenuation factor to at least one of the provisional scale factor or the first scale factor,
• wherein the second scale factor enables the amount of compressed data to fit within the target data amount.