Apparatus and methods for digital image compression
View Patent ↗Methods and systems for compression of digital images (still or motion sequences) are provided wherein predetermined criteria may be used to identify a plurality of areas of interest in the image, and each area of interest is encoded with a corresponding quality level (Q-factor). In particular, the predetermined criteria may be derived from measurements of where a viewing audience is focusing their gaze (area of interest). In addition, the predetermined criteria may be used to create areas of interest in an image in order to focus an observer's attention to that area. Portions of the image outside of the areas of interest are encoded at a lower quality factor and bit rate. The result is higher compression ratios without adversely affecting a viewer's perception of the overall quality of the image.
1. A digital image compression method comprising:
identifying a plurality of areas of interest in a sequence of related images, wherein a size of the identified areas of interest corresponds to an angular coverage of an average human fovea at a predetermined viewing distance;
determining most popular identified areas of interest that comprise less than all of the plurality of identified areas of interest; and
encoding the most popular identified areas of interest at a first quality level and unidentified areas of the image at a second and lower quality level than the most popular identified areas to produce a compressed copy of each image.
2. The method of claim 1 , further comprising creating a quantization map based on the identified areas of interest, wherein the encoding is performed based on the quantization map.
3. The method of claim 1 , wherein the sequence of related images comprises a digital motion picture.
4. The method of claim 1 , wherein the encoding is performed to provide a gradual transition in quality between an identified area of interest and an unidentified area.
5. The method of claim 1 , wherein the quality level for the unidentified areas is adjusted downward by pre-filtering the image with a spatially varying spatial frequency filter prior to encoding.
6. The method of claim 1 , wherein the areas of interest are identified while the image is partially displayed.
7. The method of claim 1 , wherein the identified areas of interest are transmitted according to level of interest, so that areas with a higher level of interest are transmitted first with successively lower interest level areas transmitted successively thereafter.
8. The method of claim 1 , further comprising enhancing the quality levels of certain unidentified areas to create additional areas of interest to draw a viewer's attention to the additional areas of interest.
9. The method of claim 8 , wherein the additional areas of interest are image areas containing at least one of a product and a name of a product.
10. The method of claim 1 , wherein encoding comprises encoding using a block discrete cosine transform.
11. A digital image compression system comprising:
means for identifying a plurality of areas of interest in a sequence of related images provided by a display, wherein a size of the identified areas of interest corresponds to an angular coverage of an average human fovea at a predetermined viewing distance;
means for determining most popular identified areas of interest that comprise less than all of the plurality of identified areas of interest; and
an encoder adapted to encode the most popular identified areas of interest at a first quality level, and unidentified areas of the image at a second and lower quality level than the most popular identified areas to produce a compressed copy of each image.
12. The system of claim 11 , further comprising a quantization map created based on the identified areas of interest, wherein the encoding is performed based on the quantization map.
13. The system of claim 11 , wherein the sequence of related images comprises a digital motion picture.
14. The system of claim 11 , wherein the encoding is performed to provide a gradual transition in quality between an identified area of interest and an unidentified area.
15. The system of claim 11 , further comprising a spatially varying spatial frequency filter, wherein the quality level for the unidentified areas is adjusted downward by pre-filtering the image using the spatial frequency filter prior to encoding.
16. The system of claim 11 , wherein the areas of interest are identified while the image is partially displayed.
17. The system of claim 11 , wherein the identified areas of interest are transmitted according to level of interest, so that areas with a higher level of interest are transmitted first with successively lower interest level areas transmitted successively thereafter.
18. The system of claim 11 , wherein the quality levels of certain unidentified areas are enhanced to artificially create additional areas of interest from the certain unidentified areas in order to draw a viewer's attention to the additional areas of interest.
19. The system of claim 18 , wherein the additional areas of interest are image areas containing at least one of a product and a name of a product.
20. The system of claim 11 , wherein the encoder performs encoding using a block discrete cosine transform.