Method and circuit for extracting histogram and cumulative distribution function for image enhancement apparatus
First Claim
1. A histogram and CDF extracting method for enhancing the quality of an image by histogram-equalizing an image signal expressed according to a predetermined number of gray levels, the method comprising the steps of:
- (a) applying only a predetermined number of upper significant bits of an input digital image signal as an address to access a data value stored in a memory at the address;
(b) increasing by “
1”
the data value stored at the address;
(c) determining a quantized histogram indicating a number of samples distributed to quantized gray levels fewer than a number of full-scale gray levels, by repeating the steps (a) and (b) for a first predetermined period of time;
(d) determining quantized CDF values by adding the number of samples for a current quantized gray level to the cumulative number of samples of all previous quantized gray levels for a second predetermined period of time in accordance with the quantized histogram determined in step (c); and
(e) linearly interpolating the quantized CDF values obtained in step (d) and outputting interpolated CDF values.
1 Assignment
0 Petitions
Accused Products
Abstract
A method for extracting a histogram and a cumulative distribution function (CDF) value for an image enhancement apparatus, and a circuit therefor are provided. The histogram extraction is performed during an active section of a video signal. The level of an input digital video signal is input as an address of a memory, and a data value stored at the address is increased. The processes are repeated during a one-screen period, thereby obtaining a histogram value indicating the number of samples distributed to each gray level. Also, a CDF value of each gray level is obtained by cumulatively integrating the number of samples from the lowest gray level on the basis of the histogram value obtained, during a vertical blanking period of the video signal. Therefore, the histogram/CDF extracting circuit can be built of simple hardware and an integrated structure, even though it performs both histogram and CDF extractions.
146 Citations
9 Claims
-
1. A histogram and CDF extracting method for enhancing the quality of an image by histogram-equalizing an image signal expressed according to a predetermined number of gray levels, the method comprising the steps of:
-
(a) applying only a predetermined number of upper significant bits of an input digital image signal as an address to access a data value stored in a memory at the address;
(b) increasing by “
1”
the data value stored at the address;
(c) determining a quantized histogram indicating a number of samples distributed to quantized gray levels fewer than a number of full-scale gray levels, by repeating the steps (a) and (b) for a first predetermined period of time;
(d) determining quantized CDF values by adding the number of samples for a current quantized gray level to the cumulative number of samples of all previous quantized gray levels for a second predetermined period of time in accordance with the quantized histogram determined in step (c); and
(e) linearly interpolating the quantized CDF values obtained in step (d) and outputting interpolated CDF values. - View Dependent Claims (2, 3, 4)
-
-
5. A histogram and cumulative distribution function (CDF) extracting circuit in an image enhancement apparatus for extracting a histogram indicating the number of samples distributed to quantized gray levels that are fewer than the number of full-scale gray levels of an input digital image signal and calculating a CDF value of each quantized gray level on the basis of the extracted histogram, a CDF interpolation circuit for linearly interpolating the CDF values extracted from the histogram/CDF extracting circuit and outputting interpolated CDF values, the circuit comprising:
-
a bit selector for selecting a predetermined number of upper significant bits of a digital image signal;
a first selector for receiving and selecting the predetermined number of the upper significant bits of the digital image signal selected by the bit selector, in a histogram extraction mode, and receiving and selecting an incrementing address, in a CDF extraction mode;
a memory for receiving from the first selector either the predetermined number of upper significant bits of the digital image signal or the incrementing address as an address signal designating a current address for accessing data, for writing a histogram value increased by “
1”
to the current address in the histogram extraction mode, and for writing a current input quantized CDF value to the current address in the CDF extraction mode;
a first buffer for receiving and temporarily storing a histogram value stored at the current address in the memory, in the CDF extraction mode;
a second selector for receiving and selecting the histogram value stored at the current address in the memory, in the histogram extraction mode, and receiving and selecting the histogram value temporarily stored in the first buffer, in the CDF extraction mode;
a second buffer for receiving and temporarily storing a quantized CDF value stored at a previous address in the memory and outputting the temporarily-stored CDF value as a previous quantized CDF value, in the CDF extraction mode;
a third selector for receiving and selecting a predetermined value “
1”
, in the histogram extraction mode, and receiving and selecting the previous quantized CDF value stored in the second buffer, in the CDF extraction mode;
an adder for adding the histogram value, stored at the current address in the memory and selected by the second selector, to the value “
1”
selected by the third selector and providing the result of the addition back to the memory to be stored at the current address, in the histogram extraction mode, and for adding the histogram value, stored in the first buffer and selected by the second selector, to the previous quantized CDF value, stored in the second buffer and selected by the third selector, and applying the result of addition back to the memory as the current quantized CDF value to be stored at the current address, in the CDF extraction mode; and
a generator for applying a selection control signal in accordance with the histogram and CDF extraction modes to the first, second and third selectors in response to the horizontal and vertical synchronous signals of the image signal, sequentially increasing the incrementing address corresponding to quantized gray levels and providing the result to the memory via the first selector in the CDF extraction mode, and generating an operation control signal for operating the memory and the first and second buffers, wherein a CDF value of each quantized gray level is output from the memory. - View Dependent Claims (6, 7, 8, 9)
-
Specification