Method and apparatus for improving the image quality of transmitted video signals via pre-filtering
AssigneeAmpex Corporation
InventorGeorge R. Varian
Life of this patent
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Abstract
A method and apparatus is disclosed which minimizes the visual artifacts normally generated when images are compressed for transfer through very narrow band channels such as, for example, the Internet. To this end, the images are pre-filtered and then scaled down prior to compression using a two dimensional spatial impulse filter with good pulse fidelity rather than flat pass bands, rapid cutoff at high frequency and minimal impulse response width. The impulse filter preferably is operated at the 6 db point down about 0.6 to 0.9 of the output image spatial band edge, thereby removing visible aliases in the images while compromising between subjective sharpness and total picture entropy.
Claims30
A method of minimizing visual artifacts generated when video images in a wide bandwidth system are compressed for use in a narrow bandwidth system wherein the wide and narrow bandwidth video images are full size input images and smaller size output images, respectively, comprising the steps of:
- supplying the wide bandwidth full size input images;
- applying two dimensional spatial impulse filtering with 6 db bandwidth substantially less than the spatial band edge for the images to be compressed, prior to compression of the video images, wherein the spatial band edge is ½d where d is the separation between distinct pixels in the images to be compressed;
- scaling down the pre-filtered full size input images to provide the smaller size output images;
- compressing the pre-filtered scaled down output images;
- and
- applying the scaled down compressed output images to said use in the narrow bandwidth system.
A method of improving the perceived image quality of a video signal supplied from a wide bandwidth system to a digital lower bit rate system comprising the steps of:
- supplying input images having an input image pixel separation;
- two dimensionally spatially impulse pre-filtering the input images at a 6 db bandwidth that is less than the spatial band edge for a resulting output image, prior to compressing the images;
- scaling down the pre-filtered images to a smaller output image size appropriate for the lower bit rate system;
- compressing the pre-filtered scaled down output images;
- transmitting the compressed output images via the lower bit rate system;
- decompressing the compressed output images;
- and
- displaying the decompressed output images with a pixel separation consistent with the output images, where the pixel separation of the output images is greater than that of the input images.
An apparatus for improving the perceived quality of output images in a narrow bandwidth system, which output images are to be transmitted thereto from a wide bandwidth system of full size input images, comprising:
- two dimensional spatial impulse filter means that are 6 db down at from 0.6 to 0.9 of the spatial band edge of the output image spatial band edge and receiving the wide bandwidth full size input images, for pre-filtering and downsizing the full size input images into the smaller down sized output images prior to compression;
- compression means receiving the pre-filtered downsized output images for compressing the output images;
- means for transferring the downsized compressed output images for use in the narrow bandwidth system;
- means for decompressing the downsized compressed output images;
- and
- display means for displaying the decompressed output images in the smaller downsized image size.
A method of maximizing perceived quality of images when transferring original input images of full size to a digital lower bit rate system of smaller size output images, comprising the steps of:
- pre-filtering the input images of the wide bandwidth system via a circularly symmetric two dimensional spatial impulse filter wherein the 6 db point is substantially less than the output image spatial band edge, prior to compressing the output images;
- scaling down the input image size of the wide bandwidth system to the smaller output image size of the digital lower bit rate system after the step of pre-filtering;
- compressing the pre-filtered scaled down output images;
- transferring the compressed output images via the digital lower bit rate system;
- and
- decompressing and displaying the decompressed output images in the smaller image size with the maximized perceived quality.
A method of improving the perceived image quality of full size input images of a video signal when digitally compressed and transmitted to a digital lower bit rate system as smaller size output images, comprising the steps of:
- two dimensionally spatially impulse pre-filtering the full size input images at full size with the resolution of the smaller size output images;
- and
- scaling down the full size pre-filtered images to provide the smaller size output images for compression, transmission and decompression in the smaller image size with the improved perceived image quality.
Apparatus for improving the perceived image quality of a video signal when compressed and transmitted to a lower bit rate system as smaller size output images, comprising:
- two dimensional spatial impulse filter means receiving the input images at full size, for pre-filtering the full size input images at the resolution of the smaller size output images;
- scaling means receiving the pre-filtered images for scaling the output images down to the smaller size;
- means for compressing the smaller size output images;
- and
- said lower bit rate system including transmission and decompression means for providing the smaller size output images at the improved perceived image quality.
Dependencies are inferred from the claim text.