As display devices of various sizes and increased resolution have been developed and the demand for them have increased, the ability for a graphics processing system to resize and resample source images and create destination images to take advantage of the various sized and higher resolution displays is a desirable operation. hi an electronic display system, color at each pixel is represented by a set of color components, and each color component is represented by a sample value. Color components such as red, green, blue (RGB) or other representations such as YCbCr are well known in the art. Whichever representation is chosen, each color component can be interpreted as a two dimensional array of samples, so three such arrays can represent images on display systems. Conceptually, resampling can be viewed as a spatial process, working on discrete input samples, represented by pixels of the source image arranged in a two-dimensional bitmap. The output samples of the destination image are spatially located at fractional sample positions within the input sample grid. Various interpolation and modeling methods are used to construct transition models between samples of the source image from which additional graphics data is produced during the resampling operation.
The additional graphics data is then used to produce larger or higher resolution destination graphics images. However, the resulting destination image must retain an acceptable image quality with respect to the source image. That is, the destination image should appear to retain at least a similar visual qualities of the source image, such as having nearly the same color balance, contrast, and brightness as the original source image. Otherwise, rather than accurately reproducing a larger or higher resolution graphics image of the source image, the resampling operation will compromise image quality by introducing image distortion. To this end, various resampling algorithms have been developed in order to create high quality destination graphics images.
With many conventional resampling algorithms, a transition model between input samples along each axis is constructed to provide output sample values. Generally good results can be obtained with separable processing along each axis for graphics images because image feature cross-sections have the same characteristics when viewed at any angle within the image plane, only at different effective sample rates. The transition models between the input samples are constructed such that the output samples interpolated from the transition model create a destination image that closely resembles the original or source image. The transition models are typically continuous so that an output sample can be generated at any position between the input samples.
Although an axis separable cubic model between two input samples can provide a model with very desirable reconstruction characteristics, algorithms for resampling and sharpening graphics data representing video often are not suitable for resizing and resampling graphics data representing test patterns containing sine-wave components. Such test patterns are called zone plates, and are characterized by a frequency component along each axis, each of which is a function of position within the pattern. The position and frequency functions are designed to change frequencies smoothly and continuously with position.
Zone plates may be embedded within patterns testing various other attributes of a video camera, storage, transmissions or display system. They are effective in testing systems with analog components (e.g., analog modulated terrestrial broadcasting), and may provide some useful tests for spectrally based compression systems (such as DCTs used in MPEG). However, these tests generally do not correspond to any attributes of the human visual system. Nevertheless, the human eye is very adept at observing large areas of inconsistency in the presentation of these patterns. Thus, to avoid viewer complaints or feelings of disappointment (whether or not they are justified), a graphics processing system having resampling and resizing capabilities should be able to accommodate these test patterns.
Therefore, there is a need for a method and system for resampling graphics data of images having sine-wave components.
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