IMAGE PROCESSING APPARATUS AND IMAGE PROCESSING METHOD

• US 20100232697A1
• Filed: 09/16/2009
• Published: 09/16/2010
• Est. Priority Date: 03/16/2009
• Status: Active Grant

• Current Assignee: Maxell, Ltd.
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Itoh, Goh, Mishima, Nao
• Granted Patent: US 8,224,110 B2
• Time in Patent Office: Days
• US Class Current: 382/168
• CPC Class Codes: G06T 2207/20012 Locally adaptive
• CPC Class Codes: G06T 2207/20192 Edge enhancement; Edge preservation
• CPC Class Codes: G06T 5/002 Denoising; Smoothing noise processing or correction adapted to be used in an image pickup device containing and electronic image sensor H04N23/81, H04N25/60 - H04N25/67
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: G06V 10/507 Summing image-intensity values; Histogram projection analysis
• CPC Class Codes: G06V 10/758 Involving statistics of pixels or of feature values, e.g. histogram matching
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/86 involving reduction of coding artifacts, e.g. of blockiness

Abstract

An image processing apparatus includes a gradient calculator that calculates a direction and a magnitude of a gradient of each pixel in an input image using neighboring pixel values; a histogram calculator that calculates a Histogram of Oriented Gradients containing plural sampled directions from the directions and the magnitudes of the gradients calculated for the pixels in a region including the pixel being processed; a storing unit that stores plural smoothing filters and associated Histograms of Oriented Gradients; a search unit that calculates errors between Histogram of Oriented Gradients calculated for the pixel being processed and the Histograms of Oriented Gradients stored in the storing unit and searches the Histogram of Oriented Gradients that has the minimum error; and a filter processing unit that acquires one of the smoothing filters stored in association with the Histogram of Oriented Gradients having the minimum error and determines a corrected pixel value of the pixel being processed by filter processing with the acquired smoothing filter.

Claims

1. An image processing apparatus comprising:

a gradient calculator configured to calculate a direction and a magnitude of a gradient of each pixel in an input image using neighboring pixel values;

a histogram calculator configured to calculate a Histogram of Oriented Gradients, which contains a plurality of sampled directions, from the directions and the magnitudes of the gradients calculated for the pixels in a region including the pixel being processed of the input image;

a storing unit configured to store a plurality of smoothing filters and a template of Histogram of Oriented Gradients s in association with each other;

a search unit configured to calculate errors between the Histogram of Oriented Gradients calculated for the pixel being processed and the Histograms of Oriented Gradients stored in the storing unit and search the Histograms of Oriented Gradients stored in the storing unit for the Histogram of Oriented Gradients that has the minimum error; and

a filter processing unit configured to acquire one of the smoothing filters that is stored in association with the Histogram of Oriented Gradients having the minimum error from the storing unit and determine a corrected pixel value of the pixel being processed by filter processing with the acquired smoothing filter.

2. The apparatus according to claim 1, wherein the search unit is configured to calculate the error by taking a sum of absolute value of a difference between the template of the Histograms of Oriented Gradients stored in the storing unit and the Histogram of Oriented Gradients calculated by the histogram calculator.

3. The apparatus according to claim 1, wherein the search unit is configured to calculate the error by taking a sum of squared value of a difference between the template of the Histograms of Oriented Gradients stored in the storing unit and the Histogram of Oriented Gradients calculated by the histogram calculator.

4. The apparatus according to claim 1, further comprising an estimating unit configured to estimate a boundary of a block in a frame, the block being a conversion unit when the input image is coded, and

wherein the histogram calculator is configured to perform control so as to cause an influence given upon calculating the Histogram of Oriented Gradients using the direction and the magnitude of the gradient between pixels striding across the estimated boundary of the block to be smaller than that when using the direction and the magnitude of the gradient between pixels not striding across the estimated boundary of the block.

5. The apparatus according to claim 1, wherein the estimating unit is configured to set in advance a predetermined block including a plurality of pixels and multiply a vector of the gradient of the pixel adjacent to the boundary of the block by a predetermined factor set in advance.

6. The apparatus according to claim 1, wherein the estimating unit is configured to estimate, as the block boundary, a boundary upon dividing the input image by a given size.

7. The apparatus according to claim 1, wherein the estimating unit is configured to obtain coding information of the input image and estimate a block size from the coding information.

8. The apparatus according to claim 1, wherein the filter processing unit is configured to determine the corrected pixel value of the pixel being processed using a weighted sum of pixel values of the pixels in the region in accordance with weighting factors determined by the filter, and

the weighting factors of the smoothing filter stored in the storing unit decrease as a distance from the pixel being processed increases, and a decreasing rate of the weighting factors is high in a direction along which the gradient of the associated Histogram of Oriented Gradients is large and is low in a direction along which the gradient of the Histogram of Oriented Gradients is small.

9. An image processing method comprising:

calculating a direction and a magnitude of a gradient of each pixel in an input image using neighboring pixel values;

calculating a Histogram of Oriented Gradients, which contains a plurality of sampled directions, from the directions and the magnitudes of the gradients calculated for the pixels in a region including the pixel being processed of the input image;

calculating, while referring to a storage unit that stores a plurality of smoothing filters and Histograms of Oriented Gradients in association with each other, errors between the Histogram of Oriented Gradients calculated for the pixel being processed and the Histograms of Oriented Gradients stored in the storing unit;

searching the Histograms of Oriented Gradients stored in the storing unit for the Histogram of Oriented Gradients that has the minimum error;

acquiring one of the smoothing filters that is stored in association with the Histogram of Oriented Gradients having the minimum error from the storing unit; and

determining a corrected pixel value of the pixel being processed by filter processing with the acquired smoothing filter.