Image luminance detection and correction employing histograms

• US 6,559,837 B1
• Filed: 09/25/2000
• Issued: 05/06/2003
• Est. Priority Date: 09/25/2000
• Status: Active Grant

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: InFocus Corporation (Lap-Shun Hui, MBA)
• Inventors: Lasneski, Alan L., Ruggiero, Carl J.
• Primary Examiner(s): Liang, Regina
• Application Number:
  US09/669,091
• Time in Patent Office: 953 Days
• Field of Search: 345/3.1, 345/3.2, 345/3.3, 345/204, 345/543, 345/544, 345/545, 345/547, 345/551, 345/552, 345/559, 345/571, 345/572, 382/168-172, 358/522, 358/523, 348/572, 348/573, 348/537, 348/536
• US Class Current: 345/204
• CPC Class Codes: H04N 5/20 Circuitry for controlling amplitude response

Abstract

A video projection display system (10) of this invention employs histograms to detect an active video region (2) of a video frame (1). A microcontroller (16) loads registers (27) in an ASIC (26) to accumulate histograms of low pixel values occurring within columns (70-74) of video data. The microcontroller scans the histograms to, identify the left-most column in which a set (80) of black pixel values is clustered, which column marks the left edge of the active video region. The right edge of the active video region is detected in a similar manner. The video signal may also include overshoot and noise. When an ADC (24) digitizes the video signal, the overshoot and noise causes many bright pixels to be converted to below their maximum digital values. Therefore, the microcontroller programs the ASIC such that a histogram (90) of the highest pixel values is collected from within the active video region. The microcontroller then scans the histogram to locate a rapid decrease in the number of pixels having values greater than some large value. Pixels having even greater values fall within the overshoot and noise range. The microcontroller remaps the upper range of data to the maximum digital values, thereby enhancing image brightness at the high end of the pixel value range.

Claims

1. In a display system in which an image is formed from a video frame organized in rows and columns of analog pixel values, the frame of data further including an inactive margin region and an active video region, an improved video frame parameter detection apparatus comprising:

at least one analog-to-digital converter digitizing the analog pixel values into digital pixel values;

at least one region register storing data corresponding to a predetermined region of the video frame, the predetermined parameter including at least one column in which the inactive margin region transitions to the active video region;

at least one histogram register sampling the digital pixel values and storing a histogram representing counts of a number of occurrences of a predetermined range of the digital pixel values occurring within the predetermined region of the video frame stored in the region register; and

a microcontroller programming the histogram register to sample the predetermined range of pixel values, programming the histogram register to sample the pixel values occurring within the predetermined region, and analyzing the resulting histogram to detect a predetermined parameter of the video frame.

2. The apparatus of claim 1 in which the histogram register is programmed such that the predetermined range of digital pixel values has a range including a blanking level value and a black pixel value.

3. The apparatus of claim 1 in which the histogram register is programmed such that the predetermined region includes at least one column of the video frame.

4. The apparatus of claim 1 in which the histogram register is programmed to sample digital pixel values including a blanking level value and a black pixel value that occur in a region including at least one column of the video frame, and in which the region in repositioned through a set of columns over a set of video frames such that the microcontroller can examine a corresponding set of histograms to determine in which column the digital pixel values transition from the blanking level value to at least the black pixel value.

5. The apparatus of claim 1 in which the display system is a video image projector.

6. The apparatus of claim 1 in which the histogram is collected during a single, frame period and updated during successive frame periods.

7. The apparatus of claim 1 in which the analog-to-digital converter has a full scale range and in which the predetermined parameter includes identifying an effective maximum pixel value in the range of digital pixel values within the active video region, wherein the effective maximum pixel value is less than a full scale pixel value and the effective maximum pixel value limits a luminance of the display system.

8. The apparatus of claim 7 in which the histogram register is programmed such that the predetermined range of digital pixel values includes the effective maximum pixel value and the full scale pixel value.

9. The apparatus of claim 7 in which the histogram register is programmed such that the predetermined region includes a majority of the active video region.

10. The apparatus of claim 7 in which the histogram register counts occurrences of digital pixel values in a range including the effective maximum pixel value and the full scale pixel value that occur within a majority of the active video region such that the microcontroller can examine the resulting histogram to determine the effective maximum pixel value and cause an analog-to-digital converter gain change that increases the effective maximum pixel value toward the full scale pixel value, thereby increasing the luminance of the display system.

11. In a display system in which an image is formed from a video frame organized in rows and columns of analog pixel values, the frame of data further including an inactive margin region and an active video region, an improved method for detecting a video frame parameter comprising:

digitizing the analog pixel values into digital pixel values;

storing a histogram representing counts of a number of occurrences of a predetermined range of the digital pixel values occurring within a predetermined region of the video frame; and

analyzing the resulting histogram to detect a predetermined parameter of the video frame, the predetermined parameter including at least one column in which the inactive margin region transitions to the active video region.

12. The method of claim 11 in which the predetermined range of digital pixel values has a range including a blanking level value and a black pixel value.

13. The method of claim 11 in which the predetermined region includes at least one column of the video frame.

14. The method of claim 11 in which the digital pixel values include a blanking level value and a black pixel value that occur in a region including at least one column of the video frame, the method further including repositioning the region through a set of columns and examining a corresponding set of histograms to determine in which column the digital pixel values transition from the blanking level value to at least the black pixel value.

15. The method of claim 11 in which the display system is a video image projector.

16. The method of claim 11 in which the histogram is collected during a single frame period and updated during successive frame periods.

17. The method of claim 11 in which the digitizing can achieve a full scale value and in which the predetermined parameter includes identifying an effective maximum pixel value in the range of digital pixel values within the active video region, wherein the effective maximum pixel value is less than a full scale pixel value and the effective maximum pixel value limits a luminance of the display system.

18. The method of claim 17 in which the predetermined range of digital pixel values includes the effective maximum pixel value and the full scale pixel value.

19. The method of claim 17 in which the predetermined region includes a majority of the active video region.

20. The method of claim 17 in which the histogram includes counts of occurrences of digital pixel values in a range including the effective maximum pixel value and the full scale pixel value that occur within a majority of the active video region, the method further including examining the resulting histogram to determine the effective maximum pixel value and changing a display system gain to increase the effective maximum pixel value toward the full scale pixel value, thereby increasing the luminance of the display system.

21. In a display system in which an image is formed from a video frame organized in rows and columns of analog pixel values, the frame of data further including an inactive margin region and an active video region, an improved video frame parameter detection apparatus comprising:

at least one analog-to-digital converter digitizing the analog pixel values into digital pixel values, the analog-to-digital converter having a full scale range;

at least one region register storing data corresponding to a predetermined region of the video frame;

at least one histogram register sampling the digital pixel values and storing a histogram representing counts of a number of occurrences of a predetermined range of the digital pixel values occurring within the predetermined region of the video frame stored in the region register; and

a microcontroller programming the histogram register to sample the predetermined range of pixel values, programming the histogram register to sample the pixel values occurring within the predetermined region, and analyzing the resulting histogram to detect a predetermined parameter of the video frame, the predetermined parameter including identifying an effective maximum pixel value in the range of digital pixel values within the active video region, wherein the effective maximum pixel value is less than a full scale pixel value and the effective maximum pixel value limits a luminance of the display system.

22. The apparatus of claim 21 in which the predetermined parameter includes the column or columns in which the inactive margin region transitions to the active video region.

23. The apparatus of claim 22 in which the histogram register is programmed such that the predetermined range of digital pixel values has a range including a blanking level value and a black pixel value.

24. The apparatus of claim 22 in which the histogram register is programmed such that the predetermined region includes at least one column of the video frame.

25. The apparatus of claim 22 in which the histogram register is programmed to sample digital pixel values including a blanking level value and a black pixel value that occur in a region including at least one columns of the video frame, and in which the region in repositioned through a set of columns over a set of video frames such that the microcontroller can examine a corresponding set of histograms to determine in which column the digital pixel values transition from the blanking level value to at least the black pixel value.

26. The apparatus of claim 21 in which the display system is a video image projector.

27. The apparatus of claim 21 in which the histogram is collected during a single frame period and updated during successive frame periods.

28. The apparatus of claim 21 in which the histogram register is programmed such that the predetermined range of digital pixel values includes the effective maximum pixel value and the full scale pixel value.

29. The apparatus of claim 21 in which the histogram register is programmed such that the predetermined region includes a majority of the active video region.

30. The apparatus of claim 21 in which the histogram register counts occurrences of digital pixel values in a range including the effective maximum pixel value and the full scale pixel value that occur within a majority of the active video region such that the microcontroller can examine the resulting histogram to determine the effective maximum pixel value and cause an analog-to-digital converter gain change that increases the effective maximum pixel value toward the full scale pixel value, thereby increasing the luminance of the display system.

31. In a display system in which an image is formed from a video frame organized in rows and columns of analog pixel values, the frame of data further including an inactive margin region and an active video region, an improved method for detecting a video frame parameter comprising:

digitizing the analog pixel values into digital pixel values including a full scale value;

storing a histogram representing counts of a number of occurrences of a predetermined range of the digital pixel values occurring within a predetermined region of the video frame; and

analyzing the resulting histogram to detect a predetermined parameter of the video frame, the predetermined parameter including identifying an effective maximum pixel value in the range of digital pixel values within the active video region, wherein the effective maximum pixel value is less than the full scale pixel value and the effective maximum pixel value limits a luminance of the display system.

32. The method of claim 31 in which the predetermined parameter includes the column or columns in which the inactive margin region transitions to the active video region.

33. The method of claim 32 in which the predetermined range of digital pixel values has a range including a blanking level value and a black pixel value.

34. The method of claim 32 in which the predetermined region includes at least one column of the video frame.

35. The method of claim 32 in which the digital pixel values include a blanking level value and a black pixel value that occur in a region including at least one column of the video frame, the method further including repositioning the region through a set of columns and examining a corresponding set of histograms to determine in which column the digital pixel values transition from the blanking level value to at least the black pixel value.

36. The method of claim 31 in which the display system is a video image projector.

37. The method of claim 31 in which the histogram is collected during a single frame period and updated during successive frame periods.

38. The method of claim 31 in which the predetermined range of digital pixel values includes the effective maximum pixel value and the full scale pixel value.

39. The method of claim 31 in which the predetermined region includes a majority of the active video region.

40. The method of claim 31 in which the histogram includes counts of occurrences of digital pixel values in a range including the effective maximum pixel value and the full scale pixel value that occur within a majority of the active video region, the method further including examining the resulting histogram to determine the effective maximum pixel value and changing a display system gain to increase the effective maximum pixel value toward the full scale pixel value, thereby increasing the luminance of the display system.