Converting an image into an output image having a higher dynamic range
An image processing device and method for converting an input image having a first dynamic range into an output image having a second dynamic range higher than the first dynamic range are provided. The image processing device includes a mapping unit for transforming an input luminance value associated with a pixel of the input image into an output luminance value associated with the corresponding pixel in the output image. The mapping unit is configured to apply a continuous and increasing function mapping a first range of values into a second range of values, whereby the highest value in the first range of values is mapped by the continuous and increasing function into a supremum of the second range of values. The mapping unit is configured to adjust the supremum depending on a peak luminance.
1 . An image processing device for converting an input image having a first dynamic range into an output image having a second dynamic range higher than the first dynamic range, the image processing device comprising:
at least one processor configured to transform an input luminance value associated with a pixel of the input image into an output luminance value associated with the corresponding pixel in the output image,
wherein the at least one processor is configured to apply a continuous and increasing function mapping a first range of values into a second range of values, whereby the highest value in the first range of values is mapped by the continuous and increasing function into a supremum of the second range of values,
wherein the at least one processor is configured to determine a peak luminance as a function of a plurality of pixel values of the input image by evaluating a measure of brightness of the input image and determining the peak luminance as a function of said measure of brightness, the peak luminance decreasing as a function of said measure of brightness, and
wherein the at least one processor is configured to adjust the supremum depending on the peak luminance.
2 . The image processing device according to claim 1 , wherein the at least one processor is configured to vary at least one parameter γ of the continuous and increasing function depending on the peak luminance.
3 . The image processing device according to claim 1 , wherein the at least one processor is configured to determine an exponent γ based on the peak luminance and exponentiate using said exponent γ.
4 . The image processing device according to claim 3 , wherein the at least one processor is configured to cause the exponent γ to increase as a function of the peak luminance.
5 . The image processing device according to claim 1 , wherein the at least one processor is configured to transform the input luminance value into an intermediate luminance value by applying a mapping function depending upon the peak luminance.
6 . A method for converting an input image having a first dynamic range into an output image having a second dynamic range higher than the first dynamic range, the method comprising:
determining a peak luminance as a function of a plurality of pixel values of the input image by evaluating a measure of brightness of the input image and determining the peak luminance as a function of said measure of brightness, the peak luminance decreasing as a function of said measure of brightness;
transforming an input luminance value associated with a pixel of the input image into an output luminance value associated with the corresponding pixel in the output image by applying a continuous and increasing function mapping a first range of values into a second range of values, whereby the highest value in the first range of values is mapped by the continuous and increasing function into a supremum of the second range of values, the supremum being adjustable depending on the peak luminance.
7 . The method according to claim 6 , wherein a parameter γ of the continuous and increasing function is variable depending on the peak luminance.