Image processing apparatus for generating a wide dynamic range image

• US 7,460,168 B2
• Filed: 05/04/2004
• Issued: 12/02/2008
• Est. Priority Date: 12/03/1998
• Status: Expired due to Fees

• Current Assignee: Olympus Corporation
• Original Assignee: Olympus Corporation
• Inventors: Horiuchi, Kazuhito
• Primary Examiner(s): Ho; Tuan V
• Application Number:
  US10/839,032
• Publication Number:
  US 20040207734A1
• Time in Patent Office: 1,673 Days
• Field of Search: 348/239, 348/222.1, 348/229.1, 348/362, 358/521, 358/518, 358/519, 358/450
• US Class Current: 348/362
• CPC Class Codes: H04N 1/4074 using histograms
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/741 by increasing the dynamic range of the image compared to the dynamic range of the electronic image sensors

Abstract

An image processing apparatus for generating a wide dynamic range image to enable contrast to be maintained in low luminance image areas and high luminance image areas when the image is displayed by a narrow density range display system having: an image data buffer in which short-time exposure image data is stored; an image area segmenting circuit for fractionating long-time exposure image data into areas of proper and improper exposure; a segmented area image information extracting circuit for segmenting the properly exposed area of the long-time exposure image data on the basis of the segmented information and segmenting the improperly exposed area as a properly exposed area by applying the short-time exposure image data; a gradation correcting circuit for gradation-correcting image data in the properly exposed areas of the long-time exposure and the short-time exposure images which have been segmented by the segmented area image information extracting means, respectively; and an image synthesizer for synthesizing the properly exposed areas after gradation correction to form a composite wide dynamic range image.

Claims

1. An image processing apparatus for generating a wide dynamic range image by processing a plurality of images photographed under different exposure conditions, the apparatus comprising:

segmenting circuitry operable to segment each of the plurality of images into properly exposed areas and improperly exposed areas in accordance with a predetermined image signal level;

image correcting circuitry to correct a gradation of the properly exposed areas of each image segmented by the segmenting circuitry; and

an image synthesizer to combine the images corrected by the image correcting circuitry into a single wide dynamic range image.

2. An apparatus according to claim 1, wherein the segmenting circuitry includes:

maximum value detecting circuitry operable to identify a maximum value of a plurality of color signals corresponding to each of the plurality of images; and

comparing circuitry operable to compare the maximum value of the color signals identified by the maximum value detecting circuitry with a predetermined image signal level, thereby enabling the properly and improperly exposed image areas to be distinguished.

3. An apparatus according to claim 1, wherein the image correcting circuitry adjusts a gradation of each of the plurality of images so that the single wide dynamic range image is approximately centered in a density range of the plurality of images.

4. An apparatus according to claim 1, wherein the image correcting circuitry includes:

feature extracting circuitry operable to extract image feature components of the images by filtering image signals respectively assigned to the plurality of images;

histogram generating circuitry operable to generate histograms from pixels near the feature components extracted by the feature extracting circuitry;

gradation correction characteristic generating circuitry operable to generate gradation correcting characteristics in accordance with the histograms generated by the histogram generating circuitry; and

gradation correcting circuitry operable to correct the graduation of the images in accordance with the gradation correction characteristics generated by the gradation correction characteristic generating circuitry.

5. An apparatus according to claim 4, wherein the histogram generating circuitry changes weighting of pixels of the images as a function of a pixel position of the image.

6. An apparatus according to claim 1, wherein the image correcting circuitry includes:

feature extracting circuitry operable to extract image feature components by filtering image signals respectively assigned to the plurality of images;

feature component histogram generating circuitry operable to generate feature component histograms for the feature components extracted by the feature extracting circuitry;

threshold value calculating circuitry operable to calculate threshold pixel luminance values from the feature component histograms;

target pixel selection circuitry operable to select target pixels from the image signals in accordance with the threshold pixel luminance values calculated by the threshold value calculating circuitry;

histogram generating circuitry operable to generate target pixel histograms from the target pixels selected by the target pixel selecting circuitry;

distribution modeling circuitry operable to adjust the histograms generated by the histogram generating circuit to a predetermined distribution;

gradation correction characteristic generating circuitry operable to generate gradation correction characteristics in accordance with the target pixel histograms and the histograms adjusted by the distribution modeling circuitry; and

gradation correcting circuitry operable to correct the graduation of the images in accordance with the gradation correction characteristics.

7. An apparatus according to claim 1, further comprising:

weighting and averaging circuitry operable to calculate a weighting-average of luminance values of pixels for a particular image pixel position when more than one luminance value has been produced for the pixel position by the image correcting circuitry; and

smoothing circuitry operable to smooth the luminance values of the pixels generated by the weighting and averaging circuitry.

8. An apparatus according to claim 1, wherein the image synthesizer includes:

an area adjusting circuit operable to compensate for a defect area in the synthesized wide dynamic range image characterized by an area which is improperly exposed in each of the plurality of images, the area adjusting circuit being operative to select luminance value for a pixel position in the defect area from an image of the plurality of images having a minimum exposure when the pixel is over-exposed, and to select a luminance value for a pixel position in the defect area from an image of the plurality of images having a maximum exposure when the pixel is under-exposed.

9. An apparatus according to claim 4, wherein the histogram generating circuitry changes weighings of the pixels of the images as a function of pixel positions of the image.