Methods and systems for improving display resolution in achromatic images using sub-pixel sampling and visual error filtering

• US 20040252218A1
• Filed: 07/08/2004
• Published: 12/16/2004
• Est. Priority Date: 06/12/2000
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Daly, Scott J., Kovvuri, Rajesh Reddy K.
• Granted Patent: US 7,194,147 B2
• Time in Patent Office: Days
• US Class Current: 348/333.01
• CPC Class Codes: G09G 2320/02 Improving the quality of display appearance
• CPC Class Codes: G09G 2340/0414 Vertical resolution change
• CPC Class Codes: G09G 2340/0421 Horizontal resolution change
• CPC Class Codes: G09G 2340/0428 Gradation resolution change
• CPC Class Codes: G09G 2340/0457 Improvement of perceived resolution by subpixel rendering
• CPC Class Codes: G09G 3/2059 using error diffusion
• CPC Class Codes: G09G 3/2074 using sub-pixels
• CPC Class Codes: G09G 5/00 Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators image data processing or generation, in general G06T
• CPC Class Codes: G09G 5/02 characterised by the way in which colour is displayed details of colour display specific for CRTs G09G1/28; specific for flat matrix panels other than liquid crystal displays G09G3/2003; specific for liquid crystal displays G09G3/3607
• CPC Class Codes: G09G 5/395 Arrangements specially adapted for transferring the contents of the bit-mapped memory to the screen G09G5/399 takes precedence

Abstract

Embodiments of the present invention provide systems and methods for converting an achromatic, higher-resolution image to a lower-resolution image with reduced visible errors. These systems and methods comprise a sub-pixel sampling performed on a higher-resolution image. The sub-pixel sampled image is then converted to an opponent color domain image that is separated into separate luminance and chrominance channels. These chrominance channels are then high-pass filtered and combined with the luminance channel to form a filtered opponent color domain image.

Claims

1. A method for converting an achromatic, higher-resolution image to a lower-resolution image with reduced visible errors, said method comprising the acts of:

performing sub-pixel sampling on said higher-resolution image;

converting said sub-pixel sampled image into an opponent color domain image;

separating said opponent color domain image into separate luminance and chrominance channels;

high-pass filtering said chrominance channels

combining said luminance, and said high-pass filtered chrominance channels into a filtered opponent color domain image.

2. The method of claim 1 further comprising the act of converting said filtered opponent color domain image into a final additive color domain image.

3. The method of claim 2 wherein said additive color domain image is an RGB image.

4. The method of claim 1 wherein said opponent color domain images are YCbCr images.

5. The method of claim 1 wherein said opponent color domain images are LAB images.

6. The method of claim 1 wherein said high-pass filtering comprises unsharp-mask filtering.

7. The method of claim 1 wherein said high-pass filtering comprises the acts of:

filtering said chrominance channels via an unsharp-mask filter with a Gaussian low-pass kernel resulting in low-pass chrominance channels and subtracting said low-pass chrominance channels from said chrominance channels to yield high-pass filtered chrominance channels.

8. A method for removing low-frequency chromatic artifacts created through sub-pixel sampling of an achromatic, higher-resolution image, said method comprising the acts of:

performing sub-pixel sampling on said higher-resolution image;

transforming said sub-pixel sampled image into an opponent color domain image with a segregated luminance channel and chrominance channels;

performing high-pass filtering on said chrominance channels to remove low frequencies which developed during sub-pixel sampling thereby creating filtered chrominance channels; and

combining said luminance channel and said filtered chrominance channels thereby creating a filtered opponent color domain image.

9. The method of claim 8 further comprising transforming said filtered opponent color domain image into a filtered additive color domain image.

10. The method of claim 8 further comprising the acts of:

copying said achromatic, higher-resolution image into component color channels;

low-pass filtering said component color channels to remove high-frequency chromatic components thereby creating filtered component color channels; and

combining said filtered component color channels into a filtered additive color domain image, said dividing, low-pass filtering and combining being performed prior to said performing sub-pixel samping.

14. The method of claim 8 further comprising the act of converting said filtered YCbCr image into a final RGB image.

15. The method of claim 8 further comprising the act of converting said filtered YCbCr image into a final RGB image.

16. The method of claim 8 wherein said high-pass filtering comprises the acts of:

filtering said Cb and Cr channels via an unsharp-mask filter with a Gaussian low-pass kernel resulting in low-pass Cb and Cr channels; and

subtracting said low-pass Cb and Cr channels from said Cb and Cr channels to yield high-pass filtered Cb and Cr channels.

11. A method for converting an achromatic, higher-resolution image to a lower-resolution image with reduced visible errors, said method comprising the acts of:

copying said achromatic, higher-resolution image into separate color channels;

low-pass filtering said separate channels;

combining said filtered channels into a filtered additive color domain image;

performing sub-pixel sampling on said filtered additive color domain image;

converting said sampled and filtered additive color domain image into an opponent color domain image;

dividing said opponent color domain image into separate luminance and chrominance channels;

high-pass filtering said chrominance channels; and

combining said luminance, and said high-pass filtered chrominance channels into a filtered opponent color domain image.

12. The method of claim 11 wherein said low-pass filtering employs a cut-off frequency of about 0.2 cycles/display pixel.

18. The method of claim 11 further comprising steps for converting said filtered opponent color domain image into a final additive color domain image.

13. A method for converting an achromatic, RGB high-resolution image to a lower-resolution image with reduced visible errors, said method comprising the acts of:

low-pass filtering said separate channels;

dividing said RGB high-resolution image into separate R, G and B channels;

combining said filtered channels into a filtered RGB image;

performing sub-pixel sampling on said filtered RGB image;

converting said filtered RGB image into a YCbCr image;

dividing said YCbCr image into separate Y, Cb and Cr channels;

high-pass filtering said Cb and Cr channels; and

combining said Y, and said filtered Cb and filtered Cr channels into a filtered YCbCr image.

17. A method for converting an achromatic, higher-resolution image to a lower-resolution image with reduced visible errors, said method comprising steps for:

separating said achromatic, high-resolution image into separate color channels;

low-pass filtering said separate channels;

combining said filtered channels into a filtered additive color domain image;

performing sub-pixel sampling on said filtered additive color domain image;

converting said sampled and filtered additive color domain image into an opponent color domain image;

dividing said opponent color domain image into separate luminance and chrominance channels;

high-pass filtering said chrominance channels combining said luminance, and said high-pass filtered chrominance channels into a filtered opponent color domain image.

19. A system for converting an achromatic, higher-resolution image to a lower-resolution image with reduced visible errors, said system comprising:

a first copier for copying said higher-resolution image into separate color channels;

a low-pass filter for filtering said separate channels;

a first combiner for combining said filtered channels into a filtered additive color domain image;

a sampler for performing sub-pixel sampling on said filtered additive color domain image;

a converter for converting said sampled and filtered additive color domain image into an opponent color domain image;

a second divider for dividing said opponent color domain image into separate luminance and chrominance channels;

a high-pass filter for filtering said chrominance channels a second combiner for combining said luminance, and said high-pass filtered chrominance channels into a filtered opponent color domain image.

20. A computer readable medium comprising instructions for converting an achromatic, higher-resolution image to a lower-resolution image with reduced errors, said instructions comprising the acts of:

separating said higher-resolution image into separate color channels;

low-pass filtering said separate channels;

combining said filtered channels into a filtered additive color domain image;

performing sub-pixel sampling on said filtered additive color domain image;

converting said sampled and filtered additive color domain image into an opponent color domain image;

dividing said opponent color domain image into separate luminance and chrominance channels;

high-pass filtering said chrominance channels; and

combining said luminance, and said high-pass filtered chrominance channels into a filtered opponent color domain image.

20-1. A computer data signal embodied in an electronic transmission, said signal having the function of converting an achromatic, higher-resolution image to a lower-resolution image, said signal comprising instructions for:

copying said high-resolution image into separate color channels;

low-pass filtering said separate channels;

combining said filtered channels into a filtered additive color domain image;

performing sub-pixel sampling on said filtered additive color domain image;

converting said sampled and filtered additive color domain image into an opponent color domain image;

dividing said opponent color domain image into separate luminance and chrominance channels;

high-pass filtering said chrominance channels combining said luminance, and said high-pass filtered chrominance channels into a filtered opponent color domain image.