Content-adaptive contrast improving method and apparatus for digital image
AssigneeHimax Technologies Limited
InventorsShing-Chia Chen, Ling-Shiou Huang
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Abstract
The present invention is directed to a digital image content-adaptive contrast improving method. The method includes forming a piecewise linear tone remapping function for a digital image according to the histogram thereof. The piecewise linear tone remapping function is formed by repeatedly performing a first and a second step. The first step determines a starting linear tone mapping function for a specific range of luminance values. The second step generates a new tone mapping function for the specific range of luminance values based on the starting linear tone mapping function and the histogram. An apparatus for implementing the method is also provided.
Claims14
A digital image content-adaptive contrast improving method, comprising the steps of:
- generating a histogram recording luminance distribution of a digital image;
- sectionalizing pixels of said digital image into a plurality of pixel groups, said pixel groups respectively covering pixels lying in exclusive luminance ranges;
- forming a piecewise linear tone remapping function for said digital image according to said histogram, said piecewise linear tone remapping function being represented by a plurality of line segments consecutively connected to each other one by one, each of said line segments representing a local linear remapping function for one of said pixel groups, comprising:
- a first step for determining a starting linear tone mapping function for a specific range of luminance values, which is between a first code value C1 and a second code value C2 greater than said first code value C1, said specific range of luminance values covering luminance values of at least two said pixel groups;
- and
- applying said piecewise linear tone remapping function to said digital image;
- wherein, said piecewise linear tone remapping function is formed by repeatedly performing said first step and a second step, wherein said specific range and said starting linear tone mapping function are different in each instance of said first and second steps.
A digital image content-adaptive contrast improving apparatus, comprising;
- a histogram generating unit configured to generate a histogram recording luminance distribution of a digital image;
- an image sectionalizing unit configured to sectionalize pixels of said digital image into a plurality of pixel groups, said pixel groups respectively covering pixels lying in exclusive luminance ranges;
- a remapping function constructing unit configured to form a piecewise linear tone remapping function for said digital image according to said histogram, said piecewise linear tone remapping function being represented by a plurality of line segments consecutively connected to each other one by one, each of said line segments representing a local linear remapping function for one of said pixel groups, wherein said remapping function constructing circuit is configured to execute a first step for determining a starting linear tone mapping function for a specific range of luminance values, which is between a first code value C1 and a second code value C2 greater than said first code value C1, said specific range of luminance values covering luminance values of at least two said pixel groups;
- and
- an image remapping unit configured to apply said piecewise linear tone remapping function to said digital image;
- said remapping function constructing circuit being configured to form said piecewise linear tone remapping function by repeatedly performing said first step and a second step, wherein said specific range and said starting linear tone mapping function are different in each occurrence of said first and second steps.
Dependencies are inferred from the claim text.