MIP map compression

1. An encoder for encoding image data, the encoder comprising:

an input arranged to receive a first image and a second image, wherein the second image is twice the width and height of the first image;

a prediction generator arranged to generate a prediction image from the first image using an adaptive interpolator,

a difference image generator arranged to generate a difference image from the prediction image and the second image;

an encoder unit arranged to encode the difference image; and

an interleaver configured to interleave blocks of data from the encoded first image and the encoded difference image to generate compressed image data.

2. The encoder according to claim 1 , wherein the first image is a first texture, the second image is a second texture, the prediction image is a prediction texture and the difference image is a difference texture.

3. The encoder according to claim 1 , wherein the compressed image data is a compressed texture.

4. The encoder according to claim 1 , further comprising:

a further encoder unit arranged to encode the first image.

5. The encoder according to claim 1 , wherein the first image received by the input is an encoded image, and the encoder further comprises:

a decoder unit arranged to decode the first image prior to generation of the difference image.

6. The encoder according to claim 1 , further comprising a data store arranged to store a plurality of vector lookup tables and wherein the encoder unit is arranged to encode the difference image using at least one of the plurality of vector lookup tables.

7. The encoder according to claim 6 , wherein the encoder unit is arranged to encode the difference image by:

sub-dividing the difference image into a plurality of sub-blocks; and

for each group of sub-blocks corresponding to a block in the encoded first image, using a single vector lookup table from the plurality of vector lookup tables to encode all the sub-blocks in the group, and recording the form of the adaptive interpolation in the prediction image in terms of a prediction mode.

8. A method of encoding image data comprising:

receiving, at an input, a first image and a second image, wherein the second image is twice the width and height of the first image;

generating, in a prediction generator, a prediction image from the first image using an adaptive interpolator,

generating, in a difference texture generator, a difference image from the prediction image and the second image;

encoding, in an encoder unit, the difference image; and

interleaving blocks of data from the encoded first image and the encoded difference image to generate compressed image data.

9. The method according to claim 8 , wherein the first image is a first texture, the second image is a second texture, the prediction image is a prediction texture and the difference image is a difference texture.

10. The method according to claim 8 , wherein the compressed image data is a compressed texture.

11. The method according to claim 8 , further comprising:

encoding the first image.

12. The method according to claim 8 , wherein the first image received by the input is an encoded image, and the method further comprises:

decoding, in a decoder unit, the first image prior to generation of the difference image.

13. The method according to claim 8 , further comprising:

accessing one or more vector lookup tables stored in a data store;

and wherein the difference image is encoded using at least one of the plurality of vector lookup tables.

14. The method according to claim 13 , wherein the difference image is encoded by:

sub-dividing the difference image into a plurality of sub-blocks; and

for each group of sub-blocks corresponding to a block in the encoded first image, using a single vector lookup table from the plurality of vector lookup tables to encode all the sub-blocks in the group, and recording the form of the adaptive interpolation in the prediction image in terms of a prediction mode.

15. A non-transitory computer readable storage medium having stored thereon a computer readable description of an integrated circuit that, when processed in an integrated circuit manufacturing system, causes the integrated circuit manufacturing system to manufacture an encoder comprising:

an input arranged to receive a first image and a second image, wherein the second image is twice the width and height of the first image;

a prediction generator arranged to generate a prediction image from the first image using an adaptive interpolator,

a difference image generator arranged to generate a difference image from the prediction image and the second image; and

an encoder unit arranged to encode the difference image, and configured to interleave blocks of data from the encoded first image and the encoded difference image to generate compressed image data.

16. The non-transitory computer readable storage medium according to claim 15 , wherein the first image is a first texture, the second image is a second texture, the prediction image is a prediction texture and the difference image is a difference texture.

17. The non-transitory computer readable storage medium according to claim 15 , wherein the compressed image data is a compressed texture.