FIELD OF INVENTION
The present invention relates to a method and system for post processing of
reconstructed images. In particular, the present invention provides a system for
reducing the effect of over smoothness and blurring in the reconstructed images.
When image reconstruction is carried out most of the energy (information) is
obtained back in the image and at the same time the image gets over
smoothened and the demarcations / edges in the image becomes too blurred.
By using post processing, a better contrast can be achieved and the quality of
the image can be restored which was over smoothened.
BACKGROUND OF THE INVENTION
US document 2007/0248277 Al discloses application of a blurring filter to the
image data for reducing contrast between some of the pixels. A stretching filter
is applied to the image data for increasing the number of pixels and a sharpening
filter is applied to the image data for increasing contrast between some of the
pixels.

The document discloses application of Gaussian blurring filter for calculating a
pixel transformation according to Gaussian distribution. An interpolation
stretching filter is applied for interpolating one or more values of one or more
neighbouring pixel for determining a value or added pixels. The application of
the sharpening filter for the image data comprises applying a filter selected in
accordance with a particular application.
In this process a blurring filter is used in the initial stage to reduce the contrast
between some pixels and this leads to blurring effects in the image. Reduction
in contrast also reduces the quality of the image.
Use of stretching filter in this document is to increase number of pixels. It
means it has to duplicate the pixels which reduces the details in the image
leading to a low quality in the image. This principle is used in zooming for
creating the new pixel locations and assigning pixel value of each pixel to the
corresponding new pixel locations. This sort of pixel replication is
computationally complex. The sharpening filter does the inverse of the first step
which should have been used in the earlier stages rather than at the last stage.
No inverse boost filter is used.

US document 5, 825, 937 discloses filtering means for performing a smoothing
process on the image data in the form of a reflectance-linear signal for
suppressing tone oscillations formed by the tone levels, said filtering means
having an output providing smoothed image data. A second filtering means is
provided for performing on the smoothed image data which has undergone the
smoothing process, an adaptive edge-enhancement process for enhancing
sharpness of edges constituting parts having steep tone gradients image. The
adaptive edge-enhancement process depends on the combination of a resolution
of input image data and a coefficient of the second filtering means, thus
selectively enhancing sharpness of portions of the image by the second filtering
means.
The smoothness introduced here blurs the edge details in the image thus
diminishing the fine details of the image and affecting its quality badly. The
adaptive edge enhancement process sharpens the edges, which makes it clearly
visible as synthetic which is not good for the quality of the image and also the
process is dependent on edge amounts present in the input image data. Here
also no inverse boost filter is used.

Document 2007/0160278 provides high-pass filtering of a first image for
obtaining a second image. The second image is processed by applying non-
linear apodization to the second image for obtaining a third image. A low pass
filter applied to the first image for obtaining a fourth image the third and fourth
images are combined to obtain an output image.
High pass filter should have been used in the later stage rather than using it in
the initial stage. The application of non-linear apodization changes the functions
to the maximum extent, instead of adding modifications for the functions. The
document only deals with the suppression of edge ringing in images, but it is
silent on or does not teach removal of blurring and over smoothness. This
document also does not use an inverse boost filter.
When deblocking filters are applied at the decoder section to remove distortion
around the edges in the image features, then there appears blurring and when
blurring takes place, the features in the image cannot be seen properly. In order
to overcome the distortions, it is necessary to apply a filter, which overcomes the
problems to the maximum extent, a filter system which can have reduced
computational complexity and simple to design. When image reconstruction

takes place, image smoothening filters are applied which result in uniform
smoothness in the image which creates difficulty in making out the features in
the image suddenly. This is nothing but an image with a degraded quality.
SUMMARY OF THE INVENTION
The main object of the present invention is to overcome the problems
encountered in the prior art for reducing the effect of blurring and over
smoothness which results after image reconstruction and provides filters which
are numerically simple to design and can adapt itself to the image content and
should have variable parameters namely, mask and strength.
Some of the novel features of the present invention includes a simple multi-filter
system design, coupling low-pass filter, inverse boost filter, high-pass filter,
statistics and averaging filter. The system has less computational complexities
and can be implemented using digital signal processor (DSP), field programmable
gate array (FPGA), configurable / complex programmable logic devices (CPLD)
and ARM, microprocessor, micro-controller or a digital computer.

It is suitable for being incorporated in an electronic product. As no image
subtraction is required, it saves processor time, power and memory needed to
store the images for the post processing. Any types of images can be used for
processing and provides better picture quality.
In a preferred embodiment the present invention provides a method for post
processing of reconstructed images, comprising the steps of: reconstructing the
image in an image processor; applying a low-pass filter (LPF) on said
reconstructed image for establishing a clear cut off between passed and filtered
frequencies; applying an inverse boost filter (IBF) to the output of said LPF to
obtain an average level of the reconstructed image; applying a Wiener
deconvolution filter to the output of said IBF to minimize the noise generated
from deconvolution process; applying a high-pass filter (HPF) to the output of
said Wiener deconvolution filter; and transferring the reconstructed image to a
statistics and averaging filter (S & AF); thereby providing better picture quality
with reduced or no over smoothness and blurring in the reconstructed images,
and providing the final output to a display / storage device.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The invention can now be described in detail with the help of the figure of the
accompanying drawing in which
Figure 1 shows in block diagram form the method
steps performed in the present invention.
DETAILED DESCRIPTION
As shown in Figure 1 reconstruction of the image is performed in an image
processor 1. A low-pass filter (LPF) 2 is applied on the reconstructed image to
establish in clear cut off between passed and filtered frequencies. The LPF is of
required order whose transfer functions does not have a sharp discontinuity.
Further, the output of the LPF 2 is given to an inverse boost filter (IBF) 3 to
obtain an average level of the reconstructed image. The output from the IBF 3
is provided to a wiener deconvolution filter 4 for minimizing the noise due to the
deconvolution process. Subsequently, the output from the

Wiener deconvolution filter 4 is provided to a high pass filter (HPF) 5 which
further transfers the reconstructed image to a statistics and averaging filter (S &
AF) 6. The statistics and averaging filter (S & AF) 6 provides the final output to
a display device or a storage device represented by block 7.
The system can be implemented with the aid of digital signal processor(DSP),
field programmable gate array (FPGA), configurable / complex programmable
logic devices (CPLD) and ARM, micro processor, micro controller or a digital
computer.
The method can be used for post processing of all types of images.
The method of the present invention requires less memory and as such uses low
power for processing as it does not use any image subtraction method. This
results in saving in both memory requirement and power thereby reducing the
overall cost.

WE CLAIM
1. A method for post processing of reconstructed images, comprising the
steps of:
- reconstructing the image in an image processor;
- applying a low-pass filter (LPF) on said reconstructed image for
establishing a clear cut off between passed and filtered
frequencies;
- applying an inverse boost filter (IBF) to the output of said LPF to
obtain an average level of the reconstructed image;
- applying a Wiener deconvolution filter to the output of said IBF to
minimize the noise generated from deconvolution process;
- applying a high-pass filter (HPF) to the output of said Wiener
deconvolution filter; and
- transferring the reconstructed image to a statistics and overaging
filter (S & AF);
thereby providing better picture quality with reduced or no over
smoothness and blurring in the reconstructed images, and providing
the final output to a display / storage device.

2. The method as claimed in claim 1, wherein said method is implemented
with the aid of digital signal processor(DSP), field programmable gate
array(FPGA), configurable/complex programmable logic devices(CPLD),
ARM, micro processor, micro controller or a digital computer.
3. The method as claimed in claim 1, wherein no image subtraction is
required which saves processor time, requiring less memory and low
power consumption.
4. A system for post processing of reconstructed images comprising:

- an image processor for reconstructing the image;
- a low-pass filter for applying on said reconstructed image for
establishing a clear cut off between passed and filtered
frequencies;
- an inverse boost filter for applying to the output of said LPF to
obtain an average level of the reconstructed image;
- a wiener deconvolution filter to the output of said IBF to minimize
the noise generated from deconvolution process;

- a high-pass filter (HPF) to the output of said wiener deconvolution
filter;
- a statistics and averaging filter for providing the final output to a
display device or to a storage device.
5. A method for post processing of reconstructed images, substantially as
herein described and illustrated in the figure of the accompanying
drawing.

The main object of the present invention is to overcome the problems
encountered in the prior art for reducing the effect of blurring and over
smoothness which results after image reconstruction and provides filters which
are numerically simple to design and can adapt itself to the image content and
should have variable parameters namely, mask and strength.