GAMMA CORRECTION APPARATUS AND METHOD CAPABLE OF PREVENTING NOISE BOOST-UP
CROSS-REFERENCE TO RELATED
APPLICATIONS
[0001] This application claims benefit under 35 U.S.C. § 119 from Korean Patent Application No. 2004-36498 filed on May 21, 2004 with the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention
[0003] The present general inventive concept relates to a gamma correction apparatus and method capable of preventing noise boost-up. More particularly, the present general inventive concept relates to a gamma correction apparatus and method capable of processing noise to prevent a noise boost-up phenomenon occurring upon gamma correction.
[0004] 2. Description of the Related Art
[0005] In image-capturing devices such as camcorders, the luminance levels of output images to input voltages have the linear characteristics as shown in line (1) of FIG. 1, whereas the luminance levels of output images to input voltages in the cathode ray tubes (CRTs) have the nonlinear characteristics as shown in line (2) of FIG. 1. Such nonlinear characteristics cause distorted images on the CRT.
[0006] Accordingly, in order to correct or compensate such an image distortion, the gamma correction is applied to an image signal shown in line (1) of FIG. 1 to produce an image signal shown in line (3) of FIG. 1 as an input to the CRT. Hence, the CRT substantially displays images having the linear characteristics shown in line (1) of FIG. 1. That is, the gamma correction increases the luminance levels of input images according to line (3) of FIG. 1 so that the CRT has output images having the linear characteristics shown in line (1) of FIG. 1.
[0007] However, the conventional gamma correction increases the luminance levels of images together with the level of noise luminance, which causes a noise boost-up phenomenon, so there exists a problem of lowering a signalto-noise ratio in the range of low-luminance levels of images displayed on the CRT.
[0008] Such a phenomenon can appear not only on a gamma correction device but also on a device having a nonlinear transfer function which relatively boosts up the low-luminance level.
SUMMARY OF THE INVENTION
[0009] The present general inventive concept has been developed in order to solve the above drawbacks and other problems associated with the conventional arrangement. Accordingly, the present general inventive concept provides a gamma correction apparatus and method capable of processing noise to prevent a noise boost-up phenomenon upon gamma correction.
[0010] Additional aspects and advantages of the present general inventive concept will be set forth in part in the
description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept.
[0011] The foregoing and other aspects and advantages of the present general inventive concept are substantially realized by providing a gamma correction apparatus capable of preventing noise boost-up, comprising a signal extraction unit to extract high-frequency signals higher than a predetermined frequency and low-frequency signals lower than the predetermined frequency from an input image signal, a temporary weight value calculation unit to calculate a predetermined temporary weight value based on the luminance level of the input image signal, a decision unit to determine high-frequency signals involved in a gamma correction of the extracted high-frequency signals based on the calculated temporary weight value, and a gamma correction unit to apply the gamma correction to the extracted high-frequency signals and low-frequency signals involved in the gamma correction.
[0012] The temporary weight value calculation unit calculates a temporary weight value to reduce a ratio of the extracted high-frequency signals involved in the gamma correction as the luminance level of the input image signal becomes lower.
[0013] Further, the temporary weight value calculation unit calculates the temporary weight value inversely proportional to the luminance level of the input image signal.
[0014] The temporary weight value calculation unit can calculate the temporary weight value based on an equation as provided below:
k = -a-Vlun + l, (0<Vta<i)
k = o, [vi^>1-];
[0015] wherein k indicates the temporary weight value, -a indicates a slope of the temporary weight value, a indicates an absolute value of the slope, and Vlum indicates the luminance level of the input image signal.
[0016] The gamma correction apparatus further comprises a slope calculation unit to calculate the absolute value of the slope based on the brightness of frames or fields including the input image signal, wherein the frames or the fields becomes brighter as the absolute value of the slope becomes smaller.
[0017] The decision unit can include a subtracter to subtract the temporary weight value smaller than '1' from '1' to calculate a final weight value to be applied to the extracted high-frequency signals, and a multiplier to multiply the final weight value and the extracted high-frequency signals to calculate high-frequency signals involved in the gamma correction.
[0018] The signal extraction unit includes a low-pass filter to extract the low-frequency signals from the input image signal, a delay unit to delay the input image signal by a phase of the extracted low-frequency signals; and a subtracter to subtract the extracted low-frequency signals from the delayed input image signal to extract the high-frequency signals.
