Imaging processing apparatus for generating a wide dynamic range image

• US 6,825,884 B1
• Filed: 11/30/1999
• Issued: 11/30/2004
• 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:
  US09/451,043
• Time in Patent Office: 1,827 Days
• Field of Search: 348/207.99, 348/218.1, 348/219.1, 348/221.1, 348/222.1, 348/229.1, 348/254, 348/255, 348/241, 348/362, 348/364, 348/256, 348/297, 358/518, 358/519, 358/520, 358/521, 358/450, 358/453, 358/433
• 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 being comprised of:

image correcting circuitry to correct a gradation of the images photographed under different exposure conditions; and

an image synthesizer to combine the gradation-corrected images into a the wide dynamic range image.

2. An apparatus according to claim 1, wherein the image correcting circuitry is operable to adjust the gradation of each of the plurality of images so that the combined wide dynamic range image is approximately in a density range of the plurality of images.

3. 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;

histogram generating circuitry operable to generate histograms from pixels of the images near the image 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.

4. An apparatus according to claim 3, wherein the histogram generating circuitry changes a weighting of the pixels of the images as a function of positions of the pixels of the image.

5. An apparatus according to claim 1, wherein the image correcting circuitry is comprised of:

feature extracting circuitry operable to extract image feature components of the images 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 circuit company;

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 selection circuitry;

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

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

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

6. An apparatus according to claim 1, wherein the image synthesizing circuit includes:

weighting and averaging circuitry operable to calculate a weighting-average of luminance values of the 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 calculated by the weighting and averaging circuitry.

7. An apparatus according to claim 1, wherein the image synthesizer includes a selection circuit operable to select a pixel having an approximately proper exposure for each pixel position of the wide dynamic range image from among the pixels of each of the plurality of gradation-corrected images.

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 a luminance value for a pixel position in the defect area from the image of the plurality of images having a minimum exposure when the pixel position is over-exposed, and to select a luminance value for a pixel position in the defect area from the image of the plurality of images having a maximum exposure when the pixel position is under-exposed.