Automatic color correction for sequences of images

• US 20040197022A1
• Filed: 04/01/2003
• Published: 10/07/2004
• Est. Priority Date: 04/01/2003
• Status: Active Grant

• Current Assignee: Avid Technology Incorporated
• Original Assignee: Avid Technology Incorporated
• Inventors: Gonsalves, Robert
• Granted Patent: US 7,684,096 B2
• Time in Patent Office: Days
• US Class Current: 382/167
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 5/007 Dynamic range modification applied in cameras using an electronic image sensor H04N23/741, H04N23/743
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/90 Dynamic range modification of images or parts thereof
• CPC Class Codes: H04N 1/6027 Correction or control of colour gradation or colour contrast H04N1/6058 takes precedence
• CPC Class Codes: H04N 1/6077 Colour balance, e.g. colour cast correction
• CPC Class Codes: H04N 23/88 for colour balance, e.g. white-balance circuits or colour temperature control

Abstract

Automatic color correction is applied to a scene or clip, including a sequence of images, in a motion picture by selecting a representative image of the scene, analyzing the image and adjusting parameters of a color correction operation that is performed on the sequence of images included in the scene. This operation can be repeated automatically for all scenes or for selected scenes in the motion picture. The parameters may be adjusted to automatically color balance the image while maintaining substantially constant contrast. Analysis of the representative image may include identifying an offset of a peak in a two-dimensional histogram of the colors in the representative image from a white point. Parameters of a color correction operation are adjusted according to this offset. Separate histograms and offsets may be determined for shadows, midtones and highlight regions of the representative image. Analysis of the representative image may include determining a one-dimensional histogram of the luminance information in the representative image. The darkest level and the brightest level in the image are used to balance the image. In particular, the histograms for color channels in the image, such as red, green and blue, are adjusted to match the darkest level and brightest level identified by the luminance histogram.

Claims

1. A method for automatic color correction of a sequence of images, comprising:

receiving an indication of one or more representative images in the sequence of images;

analyzing characteristics of the one or more representative images;

determining parameters for a color correction operation according to the analyzed characteristics of the one or more representative images; and

applying the color correction operation with the determined parameters to the sequence of images.

2. The method of claim 1, wherein analyzing characteristics of the one or more representative images comprises:

generating a two-dimensional histogram of colors in the representative image, wherein the two-dimensions include a white point; and

determining an offset between a peak value in the two-dimensional histogram and the white point.

3. The method of claim 2, wherein determining parameters comprises:

using the determined offset to determine an offset for color correction of the image.

4. The method of claim 2, wherein generating the two-dimensional histogram comprises:

for each pixel, determining a weighting for the pixel with respect to its classification as a shadow or highlight;

generating a two-dimensional histogram for each of shadows and highlights using the determined weightings for each pixel.

5. The method of claim 4, wherein determining parameters comprises:

using the determined offset for shadows to determine an offset for color correction of shadows;

using the determined offset for highlights to determine an offset for color correction of highlights; and

using the determined offsets for shadows and highlights to determine an offset for color correction of midtones.

6. The method of claim 1, wherein analyzing characteristics of the one or more representative images comprises:

generating a histogram of luminance in the representative image, whereby the histogram indicates a darkest value and a brightest value.

7. The method of claim 6, wherein determining parameters comprises:

determining adjustments to histograms of colors in the representative image to match a darkest value and a brightest value for each color to the darkest value and brightest value for the luminance.

8. A computer program product, comprising:

a computer readable medium;

computer program instructions stored on the computer readable medium that, when executed by a computer, instruct the computer to perform a method for automatic color correction of a sequence of images, comprising;

receiving an indication of one or more representative images in the sequence of images;

analyzing characteristics of the representative image;

determining parameters for a color correction operation according to the analyzed characteristics of the representative image; and

applying the color correction operation with the determined parameters to the sequence of images.

9. The computer program product of claim 8, wherein analyzing characteristics of the one or more representative images comprises:

generating a two-dimensional histogram of colors in the representative image, wherein the two-dimensions include a white point; and

determining an offset between a peak value in the two-dimensional histogram and the white point.

10. The computer program product of claim 9, wherein determining parameters comprises:

using the determined offset to determine an offset for color correction of the image.

11. The computer program product of claim 10, wherein generating the two-dimensional histogram comprises:

for each pixel, determining a weighting for the pixel with respect to its classification as a shadow or highlight; and

generating a two-dimensional histogram for each of shadows and highlights using the determined weightings for each pixel.

12. The computer program product of claim 11, wherein determining parameters comprises:

using the determined offset for shadows to determine an offset for color correction of shadows;

using the determined offset for highlights to determine an offset for color correction of highlights; and

using the determined offsets for shadows and highlights to determine an offset for color correction of midtones.

13. The computer program product of claim 8, wherein analyzing characteristics of the one or more representative images comprises:

generating a histogram of luminance in the representative image, whereby the histogram indicates a darkest value and a brightest value.

14. The computer program product of claim 13, wherein determining parameters comprises:

determining adjustments to histograms of colors in the representative image to match a darkest value and a brightest value for each color to the darkest value and brightest value for the luminance.

15. A method for analyzing characteristics of one or more representative images from a sequence of images, comprising:

generating a two-dimensional histogram of colors in the representative image, wherein the two-dimensions include a white point; and

determining an offset between a peak value in the two-dimensional histogram and the white point.

16. The method of claim 15, wherein generating the two-dimensional histogram comprises:

for each pixel, determining a weighting for the pixel with respect to its classification as a shadow or highlight; and

generating a two-dimensional histogram for each of shadows and highlights using the determined weightings for each pixel.

17. A computer program product, comprising:

a computer readable medium;

computer program instructions stored on the computer readable medium that, when executed by a computer, instruct the computer to perform a method for analyzing characteristics of one or more representative images from a sequence of images, comprising;

generating a two-dimensional histogram of colors in the representative image, wherein the two-dimensions include a white point; and

determining an offset between a peak value in the two-dimensional histogram and the white point.

18. The computer program product of claim 17, wherein generating the two-dimensional histogram comprises:

for each pixel, determining a weighting for the pixel with respect to its classification as a shadow, midtone or highlight; and

generating a two-dimensional histogram for each of shadows, midtones and highlights using the determined weightings for each pixel.

19. A method for analyzing characteristics of one or more representative images from a sequence of images, comprising:

generating a histogram of luminance in the representative image, whereby the histogram indicates a darkest value and a brightest value; and

determining adjustments to histograms of colors in the representative image to match a darkest value and a brightest value for each color to the darkest value and brightest value for the luminance.

20. A computer program product, comprising:

a computer readable medium;

computer program instructions stored on the computer readable medium that, when executed by a computer, instruct the computer to perform a method for analyzing characteristics of one or more representative images from a sequence of images, comprising;

generating a histogram of luminance in the representative image, whereby the histogram indicates a darkest value and a brightest value; and

determining adjustments to histograms of colors in the representative image to match a darkest value and a brightest value for each color to the darkest value and brightest value for the luminance.

21. A system for automatic color correction of a sequence of images, comprising:

an image analyzer having an input for receiving an indication of one or more representative images in the sequence of images and an output for providing information indicative of characteristics of the one or more representative images;

a parameter calculator having an input for receiving the information indicative of characteristics of the one or more representative images and an output for providing parameters for a color correction operation according to the analyzed characteristics of the one or more representative images.

a color corrector having a first input for receiving the parameters and a second input for receiving the sequence of images and an output for providing the sequence of images color corrected according to the determined parameters.

22. A method for automatic color correction of a sequence of clips of video information, comprising:

receiving an indication of a representative image for each clip in the sequence;

analyzing characteristics of the representative image for each clip;

determining parameters for a color correction operation for each clip according to the analyzed characteristics of the representative image for the clip; and

applying to each clip the color correction operation with the parameters determined for the clip.