Luminance preserving color conversion from YUV to RGB

• US 7,298,379 B2
• Filed: 02/10/2005
• Issued: 11/20/2007
• 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
• Primary Examiner(s): Sajous; Wesner
• Application Number:
  US11/056,372
• Publication Number:
  US 20060176313A1
• Time in Patent Office: 1,013 Days
• Field of Search: 345589-591, 345/597, 345/600, 345603-605, 382162-167, 382251-252, 382/219, 358/512, 358515-520, 348/557, 348/560, 348/577, 348/582, 348/566, 348/599, 348/612, 348/617, 348630-631, 348/635, 348/639
• US Class Current: 345/589
• 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; and

during the converting step;

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.

2. 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;

during the converting step, 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;

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.

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

receiving a first YUV signal;

converting the first YUV signal to a first RGB signal;

converting the first RG B signal to a second YUV signal; and

converting the second YUV signal to a second RGB signal, such that the luminance in the first YUV signal is essentially preserved in the second RGB signal.

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

receiving a image signal comprising first 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; and

converting the quantized RGB signal into a second YUV signal.

10. The method of color conversion from YUV color space to RGB color space recited in claim 4, wherein the quantized RGB signal is a first RGB signal, the method further comprises the step of:

converting the second YUV signal to a second RGB signal.

5. 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;

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.

6. 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, 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;

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.

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

a YUV to RGB converter that converts an image YUV signal to a first RGB signal;

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

a luminance preserving YUV to RGB converter that converts the second YUV signal to an output RGB signal.

8. 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; and

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

14. The video image color conversion system recited in claim 8 wherein the quantized RGB signal is a first RGB signal and the system further comprises:

a YUV to RGB converter that converts the second YUV signal to a second RGB signal.

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

receiving a first YUV signal;

converting the first YUV signal to a first RGB signal;

converting the first RGB signal to a second YUV signal; and

converting the second YUV signal to a second RGB signal, such that the luminance in the first YUV signal is essentially preserved in the second RGB signal,

the first YUV color signal has a first precision, and

the first RGB color signal has a second precision not less than the first precision.

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

receiving an image signal comprising first 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; and

converting the quantized RGB signal into a second YUV signal,

wherein the Quantized RGB signal is a first RGB signal, the method further comprises the step of;

converting the second YUV signal to a second RGB signal, wherein the quantized RGB color signal has a precision less than the first precision.

12. The method of color conversion from YUV color space to RGB color space recited in claim 11 wherein:

the second YUV signal has a precision greater than the precision of the quantized RGB signal; and

the second RGB signal has a precision less than the precision of the second YUV signal.

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

a YUV to RGB converter that converts an image YUV signal to a first RGB signal;

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

a luminance preserving YUV to RGB converter that converts the second YUV signal to an output RGB signal, wherein;

the first RGB color signal has a first precision;

the second YUV color signal has a second precision not less than the first precision; and

the output RGB color signal has a third precision not greater than the second precision.