Block noise level evaluation method for compressed images and control method of imaging device utilizing the evaluation method
First Claim
1. A block noise level evaluation method that evaluates a level of potential block noise arising on each block boundary in a compressed image, which is obtained by compression subsequent to division of an original image into multiple blocks of a preset number of pixels both in a horizontal direction and in a vertical direction, said block noise level evaluation method comprising the steps of:
- (a) calculating a luminance variation at each target pixel in the compressed image from luminance values of the target pixel and of an adjacent pixel adjoining to the target pixel in a preset direction;
(b) computing a smoothness degree of luminance variation at the target pixel from an anterior difference between the calculated luminance variations at the target pixel and an anterior pixel adjoining to the target pixel in the preset direction and a posterior difference between the calculated luminance variations at the target pixel and a posterior pixel adjoining to the target pixel in the preset direction;
(c) computing a block noise evaluation index from a specific ratio of an average smoothness degree of luminance variation for boundary pixels located on the block boundary to an average smoothness degree of luminance variation for inner pixels not located on the block boundary; and
(d) evaluating the level of potential block noise corresponding to the computed block noise evaluation index.
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Accused Products
Abstract
The technique of the invention converts an object RGB image into an image in a YIQ color space, calculates a luminance variation at each target pixel from Y channel values of the target pixel and an adjacent pixel adjoining to the target pixel, and computes a smoothness degree of luminance variation at the target pixel as summation of absolute values of differences between luminance variations at the target pixel and adjacent pixels. A block noise evaluation value B is obtained as a ratio of an average smoothness degree ave(psx), ave(psy) of luminance variation for boundary pixels located on each block boundary to an average smoothness degree ave(nsx), ave(nsy) of luminance variation for inner pixels not located on the block boundary. The block noise evaluation value B closer to 1 gives an evaluation result of a lower level of block noise, whereas the block noise evaluation value B closer to 10 gives an evaluation result of a higher level of block noise.
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Citations
27 Claims
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1. A block noise level evaluation method that evaluates a level of potential block noise arising on each block boundary in a compressed image, which is obtained by compression subsequent to division of an original image into multiple blocks of a preset number of pixels both in a horizontal direction and in a vertical direction,
said block noise level evaluation method comprising the steps of: -
(a) calculating a luminance variation at each target pixel in the compressed image from luminance values of the target pixel and of an adjacent pixel adjoining to the target pixel in a preset direction;
(b) computing a smoothness degree of luminance variation at the target pixel from an anterior difference between the calculated luminance variations at the target pixel and an anterior pixel adjoining to the target pixel in the preset direction and a posterior difference between the calculated luminance variations at the target pixel and a posterior pixel adjoining to the target pixel in the preset direction;
(c) computing a block noise evaluation index from a specific ratio of an average smoothness degree of luminance variation for boundary pixels located on the block boundary to an average smoothness degree of luminance variation for inner pixels not located on the block boundary; and
(d) evaluating the level of potential block noise corresponding to the computed block noise evaluation index. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A block noise level evaluation method that evaluates a level of potential block noise arising on each block boundary in a compressed image, which is obtained by compression subsequent to division of an original image into multiple blocks of a preset number of pixels,
said block noise level evaluation method comprising the steps of: -
(a) calculating a luminance variation at each target pixel in the compressed image from luminance values of the target pixel and of an adjacent pixel adjoining to the target pixel in a preset direction;
(b) computing a smoothness degree of luminance variation at the target pixel from an anterior difference between the calculated luminance variations at the target pixel and an anterior pixel adjoining to the target pixel in the preset direction and a posterior difference between the calculated luminance variations at the target pixel and a posterior pixel adjoining to the target pixel in the preset direction; and
(c) evaluating the level of potential block noise, based on the computed smoothness degrees of luminance variation for boundary pixels located on the block boundary.
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10. A control method of an imaging device that stores a compressed image, which is obtained by compression subsequent to division of an original image into multiple blocks of a preset number of pixels both in a horizontal direction and in a vertical direction, into a storage medium,
said control method comprising the steps of: -
(a) evaluating a level of potential block noise arising on each block boundary in the compressed image; and
(b) when the evaluated level of potential block noise is greater than a preset level, regenerating a compressed image with a reduced compression rate and reevaluating the level of potential block noise in the regenerated compressed image in said step (a), when the evaluated level of potential block noise is not greater than the preset level, storing the compressed image into the storage medium. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. An imaging device that stores a compressed image, which is obtained by compression subsequent to division of an original image into multiple blocks of a preset number of pixels both in a horizontal direction and in a vertical direction, into a storage medium,
said imaging device having a controller that performs control to evaluate a level of potential block noise arising on each block boundary in the compressed image, and when the evaluated level of potential block noise is greater than a preset level, to regenerate a compressed image with a reduced compression rate and to reevaluate the level of potential block noise in the regenerated compressed image, when the evaluated level of potential block noise is not greater than the preset level, to store the compressed image into the storage medium.
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24. An image storage method that stores an image, said image storage method comprising the steps of:
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(a) generating a compressed image by compression subsequent to division of an original image into multiple blocks of a preset number of pixels both in a horizontal direction and in a vertical direction;
(b) evaluating a level of potential block noise arising on each block boundary in the compressed image; and
(c) when the evaluated level of potential block noise is greater than a preset level, regenerating a compressed image with a reduced compression rate and reevaluating the level of potential block noise in the regenerated compressed image, when the evaluated level of potential block noise is not greater than the preset level, storing the compressed image into the storage medium. - View Dependent Claims (25)
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26. An image storage method that stores an image, said image storage method comprising the step of:
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when a level of potential block noise is greater than a preset level, generating a compressed image with a reduced compression rate and storing the compressed image, when the level of potential block noise is not greater than the preset level, generating a compressed image with a predetermined compression rate and storing the compressed image.
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27. An image storage method that stores an image, said image storage method comprising the step of:
when a level of potential block noise is greater than a preset level, storing a compressed image with a reduced compression rate and a compressed image with a predetermined compression rate.
Specification