Generating output pixels of an output image from one or more input images using a set of motion vectors having a sub-pixel accuracy

1. An image processing apparatus in which output pixels of an output image are generated from one or more input images using a set of motion vectors having a sub-pixel accuracy, the apparatus comprising:

a processor configured to:

allocate motion vectors in the set to pixels of the output image, the motion vector allocator being arranged to compare a current output pixel with test image areas pointed to by motion vectors in the set to detect a most suitable motion vector for the current output pixel; and

generate the output pixels, the processor operating in a first mode if the output pixel is within a threshold displacement from an image region having substantially different motion characteristics to those of that output pixel, and in a second mode otherwise, by applying a first spatial filter for generating an output pixel value at a required pixel position to a sub-pixel accuracy;

in which:

in the first mode, the first spatial filter is applied to a group of pixel values derived from the input image(s) such that the group does not extend into an image area having different motion characteristics to those of the output pixel by re-using pixel values from an image area having the same motion characteristics as those of the output pixel, so that at least one such pixel value is applied to more than one non-zero filter tap of the first spatial filter; and

in the second mode, the first spatial filter is applied to a group of pixel values derived from the input image(s), there being one such pixel value for each non-zero filter tap.

2. The image processing apparatus according to claim 1 , in which:

the processor is configured to apply a second spatial filter for comparing the current output pixel and a test image area to a sub-pixel accuracy; and

the second spatial filter has fewer filter taps than the first spatial filter.

3. The image processing apparatus according to claim 1 , in which an output image is derived from at least two input images.

4. The image processing apparatus according to claim 1 , in which the input images are images of an input video signal and the output image is an image of an output video signal.

5. The image processing apparatus according to claim 1 , the apparatus being a scan conversion apparatus.

6. An image processing method in which output pixels of an output image are generated from one or more input images using a set of motion vectors having a sub-pixel accuracy, the method comprising:

allocating motion vectors in the set to pixels of the output image by comparing a current output pixel with test image areas pointed to by motion vectors in the set to detect a most suitable motion vector for the current output pixel; and

generating the output pixels in a first mode if the output pixel is within a threshold displacement from an image region having substantially different motion characteristics to those of that output pixel, and in a second mode otherwise, by applying a spatial filter to generate an output pixel value at a required pixel position to a sub-pixel accuracy;

in which:

in the first mode the spatial filter is applied to a group of pixel values derived from the input image(s) such that the group does not extend into an image area having substantially different motion characteristics, to those of the output pixel by re-using pixel values from an image area having the same motion characteristics as those of the output pixel, so that at least one such pixel value is applied to more than one non-zero filter tap of the spatial filter; and

in the second mode the spatial filter is applied to a group of pixel values derived from the input image(s), there being one such pixel value for each non-zero filter tap.

7. A non-transitory computer-readable medium including computer software having program code which, when executed by a computer, is arranged to cause the computer to carry out a method according to claim 6 .