System and process for improving the uniformity of the exposure and tone of a digital image

A system for generating a composite image that exhibits an improved uniformity in both exposure and tone in comparison to a set of input images each of which exhibits a different exposure level, the system comprising:

• a general purpose computing device;
• a computer program comprising program modules executable by the computing device, wherein the computing device is directed by the program modules of the computer program to,
• access said set of digital images;
• generate the composite image by setting each pixel in the composite image to a pixel brightness level that influences the exposure and tone of the pixel based on the distribution of the pixel brightness levels of the pixels of each image in the set of images, wherein said generating comprises,
• generating a n-dimensional histogram from the brightness values associated with each pixel of each image in the set of images, wherein n is equal to the number of images in the set of images,
• fitting a curve to the histogram data,
• for each data point of the histogram,
• projecting the histogram data point onto a point of the curve which is nearest to the data point,
• identifying a new pixel brightness value associated with the point of the curve coinciding with the projected histogram data point, and
• associating the identified new pixel brightness value with the pixel corresponding to the projected data point, and
• generating the composite image by using the new pixel brightness value associated with each pixel of one of the images of the set of images as a substitute for an original brightness value of the pixel.

A computer-readable memory for causing a computing device to generate a composite image that exhibits an improved uniformity in both exposure and tone in comparison to a set of input images each of which exhibits a different exposure level, comprising:

• a computer-readable storage medium;
• and
• a computer program comprising program modules stored in the storage medium, wherein the storage medium is so configured by the computer program that it causes the computing device to,
• access said set of digital images;
• generate the composite image by setting each pixel in the composite image to a pixel brightness level that influences the exposure and tone of the pixel based on the distribution of the pixel brightness levels of the pixels of each image in the set of images, wherein said generating comprises,
• generating a n-dimensional histogram from the brightness values associated with each pixel of each image in the set of images, wherein n is equal to the number of images in the set of images,
• fitting a curve to the histogram data,
• for each data point of the histogram,
• projecting the histogram data point onto a point of the curve which is nearest to the data point
• identifying a new pixel brightness value associated with the point of the curve coinciding with the projected histogram data point, and
• associating the identified new pixel brightness value with the pixel corresponding to the projected data point, and
• generating the composite image by using the new pixel brightness value associated with each pixel of one of the Images of the set of images as a substitute for an original brightness value of the pixel.

A digital camera comprising:

• a computing device comprising a component for generating a composite image that exhibits an improved uniformity in both exposure and tone in comparison to a set of images captured by the digital camera;
• a computer program comprising program modules executable by the computing device, wherein the computing device is directed by the program modules of the computer program to,
• cause the digital camera to create the set of digital images each of which is captured at a different exposure level;
• generate the composite image by setting each pixel in the composite image to a pixel brightness level that influences the exposure and tone of the pixel based on the distribution of the pixel brightness levels of the pixels of each image in the set of images, wherein said generating comprises,
• generating a n-dimensional histogram from the brightness values associated with each pixel of each image in the set of images, wherein n is equal to the number of images in the set of images,
• fitting a curve to the histogram data,
• for each data point of the histogram,
• projecting the histogram data point onto a point of the curve which is nearest to the data point,
• identifying a new pixel brightness value associated with the point of the curve coinciding with the projected histogram data point, and
• associating the identified new pixel brightness value with the pixel corresponding to the projected data point, and
• generating the composite image by using the new pixel brightness value associated with each pixel of one of the images of the set of images as a substitute for an original brightness value of the pixel.

A computer-implemented image manipulation process for generating a composite image from a set of digital images of a static scene which were captured at different exposure levels, wherein the composite image exhibits an improved uniformity in both exposure and tone in comparison to the set of images, said process comprising using a computer to perform the following steps:

• accessing the set of digital images;
• generating the composite image by setting each pixel in the composite image to a pixel brightness level that influences the exposure and tone of the pixel based on the distribution of the pixel brightness levels of the pixels of each image in the set of images, said generating comprising,
• generating a n-dimensional histogram from the brightness values associated with each pixel of each image in the set of images, wherein n is equal to the number of images in the set of images,
• fitting a curve to the histogram data,
• for each data point of the histogram
• projecting the histogram data point onto a point of the curve which is nearest to the data point,
• identifying a new pixel brightness value associated with the point of the curve coinciding with the projected histogram data point, and
• associating the identified new pixel brightness value with the pixel corresponding to the projected data point, and
• generating the composite image by using the new pixel brightness value associated with each pixel of one of the images of the set of images as a substitute for an original brightness value of the pixel.

A computer-implemented process for generating a composite image from a set of digital images of a static scene, which exhibits an improved uniformity in both exposure and tone in comparison to the set of images, said process comprising using a computer to perform the following steps:

• inputting the set of digital images each of which is captured at a different exposure level;
• computing a summed brightness level for each pixel set in the set of images by adding the brightness level exhibited by each pixel in a pixel set, wherein a pixel set comprises a pixel from each image of the image set which represents the same portion of the scene depicted by the set of images;
• dividing the summed brightness level computed for each pixel set by the number of images in the set of images to produce an average brightness level;
• generating the composite image by using the average pixel brightness level associated with each pixel set as the brightness value for a pixel in the composite image corresponding to the location of the pixels of the pixel set in the scene depicted by the set of images.

A system for generating a composite image that exhibits an improved uniformity in both exposure and tone in comparison to a set of input images each of which exhibits a different exposure level, the system comprising:

• a general purpose computing device;
• a computer program comprising program modules executable by the computing device, wherein the computing device is directed by the program modules of the computer program to,
• compute a summed brightness level for each pixel set in the set of images by adding the brightness level exhibited by each pixel in a pixel set, wherein a pixel set comprises a pixel from each image of the image set which represents the same portion of the scene depicted by the set of images,
• generate a cumulative distribution function based on a count of the number of pixel sets having the same summed brightness level,
• normalize the cumulative distribution function so that a maximum cumulative count value thereof corresponds to a maximum possible summed brightness level, and
• generate the composite image by using the normalized cumulative distribution function to identify a cumulative count value that corresponds to the summed brightness level for each pixel set, dividing the cumulative count value of each pixel set by the number of images in the image set to produce a composite pixel brightness level for that pixel set, and using the composite pixel brightness level associated with each pixel set as the brightness value for a pixel in the composite image corresponding to the location of the pixels of the pixel set in the scene depicted by the set of images.

A computer-readable medium having computer-executable instructions for causing a computing device to generate a composite image that exhibits an improved uniformity in both exposure and tone in comparison to a set of input images each of which exhibits a different exposure level, said computer-executable instructions comprising:

• computing a summed brightness level for each pixel set in the set of images by adding the brightness level exhibited by each pixel in a pixel set, wherein a pixel set comprises a pixel from each image of the image set which represents the same portion of the scene depicted by the set of images;
• generating a cumulative distribution function based on a count of the number of pixel sets having the same summed brightness level;
• normalizing the cumulative distribution function so that a maximum cumulative count value thereof corresponds to a maximum possible summed brightness level;
• blending the normalized cumulative distribution function with a straight line function to produce a blended distribution function, said blended distribution function reducing the effects of noise on the distribution function caused by large areas of a single color in the scene depicted in the set of images;
• and
• generating the composite image by using the blended distribution function to identify a cumulative count value that corresponds to the summed brightness level for each pixel set, dividing the cumulative count value of each pixel set by the number of images in the image set to produce a composite pixel brightness level for that pixel set, and using the composite pixel brightness level associated with each pixel set as the brightness value for a pixel in the composite image corresponding to the location of the pixels of the pixel set in the scene depicted by the set of images.

A digital camera comprising:

• a computing device comprising a component for generating a composite image that exhibits an improved uniformity in both exposure and tone in comparison to a set of images captured by the digital camera;
• a computer program comprising program modules executable by the computing deice, wherein the computing device is directed by the program modules of the computer program to,
• cause the digital camera to create the set of digital images each of which is captured at a different exposure level,
• compute a summed brightness level for each pixel set in the set of images by adding the brightness level exhibited by each pixel in a pixel set, wherein a pixel set comprises a pixel from each image of the image set which represents the same portion of the scene depicted by the set of images,
• divide the summed brightness level computed for each pixel set by the number of images in the set of images to produce an average brightness level, and
• generate the composite image by using the average pixel brightness level associated with each pixel set as the brightness value for a pixel in the composite image corresponding to the location of the pixels of the pixel set in the scene depicted by the set of images.