Display technology is growing at tremendous rate. Image processing has shifted from analog processing to digital processing and high definition display panels are now the most commonly used technology in present day television sets. However, low resolution video content must continue to be supported and a desire exists to display such content on high resolution displays. There is accordingly a demand for effective image processing solutions that can display low resolution video with high clarity and quality. Consumers desire the display of low resolution video content in a manner perceived equal with respect to high resolution video content.
Reference is now made to FIG. 1 which illustrates a block diagram of a conventional image restoration and enhancement system 10. The system 10 includes a low resolution (standard definition) processing domain 12 and a high resolution (high definition) processing domain 14.
In the low resolution processing domain 12, a low resolution (raw) video signal 16 is received by a pre-scaler domain image restoration block 42 which performs a noise reduction 18 operation. Thus, image restoration in the pre-scaler domain signal processing, known to those skilled in the art, is performed on the low resolution video signal 16.
The noise cleaned low resolution signal 20 output from the pre-scaled domain image restoration block 18 is then processed by a scaling with enhancement block for conversion into a high resolution video signal 32. The scaling with enhancement block comprises two stages: a first stage 40 formed by a vertical scaling and sharpness block 22 and a second stage 44 formed by a horizontal scaling and sharpness block 30. The vertical scaling and sharpness block 22 functions based on polyphase filtering. The system 10 further includes a look-up table 26 for storing polyphase filter coefficients for the block 22. The vertical scaling and sharpness block 22 also includes a line memory bank block 28 which comprises a memory for storing video data in connection with the vertical scaling and sharpness polyphase filter processing. Operation of the vertical scaling and sharpness block 22 is known to those skilled in the art. The vertically processed video signal 24 output from the block 22 is then processed by the horizontal scaling and sharpness block 30 for conversion into the high resolution video scaled output signal 32. The horizontal scaling and sharpness block 30 functions based on polyphase filtering. The system 10 further includes a look-up table 34 for storing the polyphase filter coefficients for the block 30. Vertical scaling with sharpness block 40 and horizontal scaling with sharpness block 44 processing exist as separate instances for the luma and chroma paths.
In the high resolution processing domain 14, the high resolution video signal 32 is received by a post-scaler edge domain image enhancement block 46 which performs an edge enhancement and detail sharpness 36 operation to produce a high resolution processed video output 38. Post scalar domain image enhancement 46 is performed only on the luma from the scalar block. Scaled chroma is delayed to match with the post scalar luma processing. Thus, image enhancement in the post-scaler domain signal processing, known to those skilled in the art, is performed on the high resolution video signal 32. The image enhancement block 46 also includes a line memory bank block 48 which comprises a memory for storing luminance data for the 2D processing in the post scalar domain. 2D luminance data in the post scalar domain mainly involves fine texture sharpness and edge enhancement processing.
The performance and results of the system 10 are unacceptable for a number of reasons including:
1. The pre-scaler domain image restoration block 42 implicates noise reduction prior to image scaling. This operation can lead to a loss of fine textures and detail loss due to poor performance, and these losses are irreversible. Poor adaptation to texture and noise can lead to loss of texture during the process of noise reduction.
2. The vertical and horizontal scaling filters in blocks 22 and 30 are designed to scale the image into the high resolution domain with a single wide band polyphase filter. The scaling weights common for noise and texture region assumes that the image restoration is fool proof. However, any stray remnants of noise present after restoration can be scaled into the high resolution domain, and these remnants cannot be removed in the post scaled domain; rather, post scaled domain image restoration is a costly solution.
3. The vertical and horizontal sharpness which are embedded with the scaling filter can also enhance the stray remnants of noise removed in the restoration block. Typically, the noise cleaned region should not be sharpened during image enhancement. Further, in design, separable vertical and horizontal one dimension sharpness is applied. This can lead to jaggedness in the slant edges amplified by the sharpness.
4. Image enhancement is performed over entire image irrespective of whether the edge is in the noisy region or in the texture region. This can lead to stray noise in the shapes of textures in the post scaled domain. Normally any edge enhancement for the noise cleaned region should be switched off.
A need thus exists in the art for an improved image processing system which supports the conversion of low resolution video for high resolution display using an adaptive approach.
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