Method and apparatus for compressing and decompressing data

A method for compressing electronic image data comprising a plurality of elements, comprising:

• generating modulation values and at least two sets of reduced size image data from the electronic image data, each element of each set of reduced size image data being representative of a plurality of elements of the electronic image data, wherein the sets of reduced size image data can be combined using the modulation values to provide a representation of the electronic image data;
• for each of a plurality of groups of modulation values, assigning a set of bits of modulation data, wherein the set of bits of modulation data assigned to encode a group of modulation values comprises:
• (i) a plurality of modulation indicators for a respective plurality of modulation values in the group, the modulation indicators for the group indicating which of a set of one or more candidate modulation values are to be used to represent the modulation values in the group;
• and
• (ii) a plurality of modulation value choice bits indicating the set of one or more candidate modulation values for the group;
• and
• storing the sets of reduced size image data, and the sets of bits of modulation data for the groups of modulation values.

A method for decompressing compressed image data to produce electronic image data comprising a plurality of elements, comprising:

• receiving modulation values and at least two sets of reduced size image data, each element of each set of reduced size image data being representative of a plurality of elements of the electronic image data, wherein the sets of reduced size image data can be combined using the modulation values to provide a representation of the electronic image data, wherein a set of bits of the received modulation data is assigned for each of a plurality of groups of modulation values, wherein the set of bits of modulation data assigned to encode a group of modulation values comprises:
• (i) a plurality of modulation indicators for a respective plurality of modulation values in the group, the modulation indicators for the group indicating which of a set of one or more candidate modulation values are to be used to represent the modulation values in the group;
• and
• (ii) a plurality of modulation value choice bits indicating the set of one or more candidate modulation values for the group;
• upscaling the at least two sets of reduced size image data;
• using the respective set of bits of modulation data for each of the groups to determine the modulation values for that group of modulation values;
• and
• combining the at least two upscaled sets of reduced size image data using the determined modulation values to produce decompressed electronic image data.

Apparatus for decompressing compressed image data to derive electronic image data comprising a plurality of elements, comprising:

• a cache for receiving at least two sets of reduced size image data, each element of the two sets of reduced size image data being representative of a plurality of elements of the electronic image data;
• an upscaler for upscaling the at least two sets of reduced size image data;
• a modulation data unit for receiving modulation values, wherein a set of bits of the received modulation data is assigned for each of a plurality of groups of modulation values, wherein the set of bits of modulation data assigned to encode a group of modulation values comprises:
• (i) a plurality of modulation indicators for a respective plurality of modulation values in the group, the modulation indicators for the group indicating which of a set of one or more candidate modulation values are to be used to represent the modulation values in the group;
• and
• (ii) a plurality of modulation value choice bits indicating the set of one or more candidate modulation values for the group;
• wherein the modulation data unit is configured to use the respective set of bits of modulation data for each of the groups to determine the modulation values for that group of modulation values;
• and
• a blending unit for combining the at least two upscaled sets of reduced size image data using the determined modulation values to derive decompressed electronic image data.

A method for compressing electronic image data comprising two sets of elements which are arranged in an alternating pattern, comprising:

• generating at least two sets of reduced size image data from the electronic image data, each element of each set of reduced size image data being representative of a plurality of elements of the electronic image data;
• assigning a modulation value for each of the elements of a first of the two sets of elements of the electronic image data;
• and
• assigning a respective flag corresponding to each of the elements of a second of the two sets of elements of the electronic image data, wherein the flag assigned for an element of the second set indicates whether a modulation value for that element is to be derived by interpolating adjacent horizontal elements or adjacent vertical elements.

A method for decompressing compressed image data to produce electronic image data comprising two sets of elements which are arranged in an alternating pattern, comprising:

• receiving at least two sets of reduced size image data, each element of each set of reduced size image data being representative of a plurality of elements of the electronic image data;
• upscaling the at least two sets of reduced size image data;
• receiving an indication of a modulation value for each of the elements of a first of the two sets of elements of the electronic image data;
• receiving a respective flag for each of the elements of a second of the two sets of elements of the electronic image data;
• using the received indications to determine modulation values of the elements of the first of the two sets of elements of the electronic image data;
• for each element of the second of the two sets of elements of the electronic image data, deriving a modulation value for the element by interpolating adjacent horizontal elements when said flag for the element has a first value, and deriving a modulation value for the element by interpolating adjacent vertical elements when said flag for the element has a second value;
• and
• blending the at least two upscaled sets of reduced size image data for each element using the thus determined respective modulation values to produce decompressed electronic image data for each element.

Apparatus for decompressing compressed image data to produce electronic image data comprising two sets of elements which are arranged in an alternating pattern, comprising:

• a cache for receiving at least two sets of reduced size image data, each element of each set of reduced size image data being representative of a plurality of elements of the electronic image data;
• an upscaler for upscaling the at least two sets of reduced size image data;
• a modulation data unit for:
• (i) receiving an indication of a modulation value for each of the elements of a first of the two sets of elements of the electronic image data, (ii) using the received indications to determine modulation values of the elements of the first of the two sets of elements of the electronic image data, and (iii) receiving a respective flag for each of the elements of a second of the two sets of elements of the electronic image data;
• a blending unit for blending the at least two upscaled sets of reduced size image data for each element using the thus determined respective modulation values;
• and
• an interpolation unit for interpolating image data for each element of the second of the two sets of elements using either horizontally adjacent or vertically adjacent elements in dependence on the value of the flag received for each element of the second of the two sets of elements of the electronic image data.