Method and apparatus for dynamic image contrast expansion

A method of dynamic image contrast expansion used for processing an inputted image, comprising the steps of:

• using an inputted image gamma conversion unit for performing a gamma conversion for an inputted image to convert the relation of the brightness and gray level of said inputted image into a linear relation;
• using an image dynamic contrast expansion unit for analyzing an image property histogram of said inputted image to compute a maximum gray level and a minimum gray level required for computing an image contrast expansion, and said maximum gray level and said minimum gray level are used in the following formula:
• k
• =
• 255
• max
• -
• min
• to obtain an image contrast expansion gain k;
• and using the following formula for computing a dynamic contrast expansion:
• Gray′=k×(Gray−min),
• wherein said minimum gray level is an average of the minimum gray levels of a plurality of previously inputted images and the minimum gray level of a current image used as the minimum gray level in a dynamic contrast expansion formula, so as to compute a new gray level value outputted after said image contrast expansion is performed.

An apparatus for dynamic image contrast expansion used for processing an inputted image, comprising:

• an inputted image gamma conversion unit, for performing a gamma conversion to said inputted image, so that a linear relation exists between the gray level and brightness of said image;
• and
• an image dynamic contrast expansion unit, for analyzing an image property histogram to compute a maximum gray level and a minimum gray level required for computing said image contrast expansion, and then using the following formula to determine an image contrast expansion gain k:
• k
• =
• 255
• max
• -
• min
• ,
• wherein said image dynamic contrast expansion unit comprises an image contrast expansion gain average processing unit, such that if said average processing unit performs a dynamic contrast expansion according to the following formula:
• Gray′=k×(Gray−min),
• wherein said contrast expansion gain is given by the following formula:
• k
• out
• =
• 1
• N
• ⁢
• ∑
• i
• =
• 1
• N
• ⁢
• k
• i
• to obtain an average kout of a plurality of previous image contrast expansion gains k1˜kN−1 and a current image contrast expansion gain kNused as a gain in a dynamic contrast expansion formula to compute a new gray level value Gray′ of an outputted image after said image contrast expansion is performed for the gray level value Gray of said inputted image.

An apparatus for dynamic image contrast expansion, used for processing an inputted image, comprising:

• a gamma conversion unit of an inputted image, for performing a gamma conversion to said inputted image, such that a linear relation exists between the gray level and brightness of said image;
• and
• an image dynamic contrast expansion unit, for analyzing an image property histogram to compute a maximum gray level and a minimum gray level required for computing an image contrast expansion and uses the following formula to determine an image contrast expansion gain k:
• k
• =
• 255
• max
• -
• min
• ,
• wherein said image dynamic contrast expansion unit comprises an image contrast expansion gain average processing unit, and said average processing unit performs a dynamic contrast expansion according to the following formula:
• Gray′=k×(Gray−min),
• wherein said minimum gray level (min) is computed by the following formula:
• min
• out
• ⁢
• =
• 1
• N
• ⁢
• ∑
• i
• =
• 1
• N
• ⁢
• min
• i
• to obtain an average minout of the minimum gray levels min1˜minN−1 of a plurality of previous inputted images and the minimum gray level minN of a current image as a minimum gray level for a dynamic contrast expansion formula and compute a new outputted gray level value after said image contrast expansion is performed.