Luminance preserving color conversion from YUV to RGB

• US 20060176313A1
• Filed: 02/10/2005
• Published: 08/10/2006
• Est. Priority Date: 02/10/2005
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Yeong-Taeg, Xu, Ning
• Granted Patent: US 7,298,379 B2
• Time in Patent Office: Days
• US Class Current: 345/603
• CPC Class Codes: H04N 9/67 for matrixing camera processing pipelines for matrixing of colour signals H04N23/85

Abstract

This invention presents a YUV to RGB conversion method which preserves high precision of luminance information in an original YUV image signal when converting it to RGB signal. The method can be used to convert the original YUV signal to arbitrary quantization levels in RGB space. In addition, this invention presents methods of pre-quantization and re-quantization as to compensate conventional YUV to RGB color conversion.

Claims

1. A method of color conversion from YUV color space to RGB color space, comprising the steps of:

receiving a image signal comprising YUV signals having a first precision;

converting the image signal into a quantized RGB signal having a second precision;

such that the luminance of the image signal is essentially preserved in the quantized RGB signal.

2. The method of claim 1 wherein the step of converting further includes the steps of essentially minimizing the quantization error in luminance information of the image signal by trading off the quantization error in chrominance information of the image signal.

3. The method of claim 2 wherein the step of essentially minimizing the quantization error in luminance information of the image signal, further includes the steps of constraining chrominance errors while essentially minimizing luminance quantization errors.

4. The method of claim 2 wherein the step of essentially minimizing the quantization error in luminance information of the image signal, further includes the steps of constraining chrominance errors while essentially minimizing luminance quantization errors to keep the color difference between the image signal and the quantized RGB signal within a tolerable range.

5. The method of claim 1 wherein the steps of converting further includes the steps of formulating and solving a constrained minimization problem to essentially preserve the luminance of the original signal in the quantized RGB signal.

6. The method of claim 1 wherein the steps of converting further includes the steps of essentially minimizing luminance errors while ensuring that the chrominance difference before and after conversion is constrained.

7. The method of claim 1 wherein the conversion step further includes the steps of:

determining a set of possible RGB signal values for the quantized signal such that the difference in chrominance before and after conversion is constrained; and

selecting an RGB signal value from the above possible RGB signal values that essentially minimizes the difference in luminance before and after conversion.

8. The method of claim 7 wherein the set of possible RGB signal values (R,G,B) for the quantized RGB signal is within a range defined as:

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wherein r, g and b represent the image signal values.

9. A method of RGB color signal re-quantization comprising the steps of:

re-converting the quantized RGB signal into a second YUV signal; and

converting the second YUV signal to an output RGB signal, using the method of claim 1.

10. A method of YUV color signal pre-quantization comprising the steps of:

converting the input YUV signal to an RGB signal, using the method of claim 1, and converting the resulting RGB signal into YUV signal.

11. A video image color conversion system, comprising:

a converter that receives an image signal comprising YUV signals having a first precision, and converts the image signal into a quantized RGB signal having a second precision, such that the luminance of the image signal is essentially preserved in the quantized RGB signal.

12. The system of claim 11 wherein the converter further essentially minimizes the quantization error in luminance information of the image signal by trading off the quantization error in chrominance information of the image signal.

13. The system of claim 12 wherein the converter further essentially minimizes the quantization error in luminance information of the image signal, by constraining chrominance errors while essentially minimizing luminance quantization errors.

14. The system of claim 12 wherein the converter further essentially minimizes the quantization error in luminance information of the image signal, by constraining chrominance errors while essentially minimizing luminance quantization errors to keep the color difference between the image signal and the quantized RGB signal within a tolerable range.

15. The system of claim 11 wherein the converter further solves a constrained minimization problem to essentially preserve the luminance of the original signal in the quantized RGB signal.

16. The system of claim 11 wherein the converter further essentially minimizes quantization errors in luminance of the image signal while ensuring that the difference in chrominance before and after quantization is constrained.

17. The system of claim 11 wherein the converter further determines a set of possible RGB signal values for the quantized signal such that the difference in chrominance before and after conversion is constrained, and further selects an RGB signal value from the above possible RGB signal values that essentially minimizes the difference in luminance before and after conversion.

18. The system of claim 17 wherein the set of possible RGB signal values (R,G,B) for the quantized RGB signal is within a range defined as:

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wherein r, g and b represent the image signal values.

19. A video image color signal re-quantization system, comprising:

an RGB to YUV converter that converts the quantized RGB signal into a second YUV signal; and

a luminance preserving YUV to RGB converter as in claim 11 that converts the second YUV signal to an output RGB signal.

20. A video image color pre-quantization system, comprising:

a luminance preserving YUV to RGB converter as in claim 11, and

an RGB to YUV converter that converts the resulting RGB signal into YUV signal.