Image processing apparatus and image processing method capable of reducing an increase in coding distortion due to sharpening
View Patent ↗According to one embodiment, an image processing apparatus includes a decoder, an acquisition module, a sharpening module, and a controller. The decoder decodes an encoded image to obtain a decoded image. The acquisition module acquires quantization information indicating the accuracy of quantization upon generating the encoded image. The sharpening module performs sharpening on the decoded image. The controller controls the effect of the sharpening based on the quantization information such that the effect of the sharpening is reduced as the accuracy decreases.
1. An image processing apparatus comprising:
a processor configured to function as:
a decoder configured to decode an encoded image to obtain a decoded image;
an acquisition module configured to acquire quantization information indicating accuracy of quantization upon generating the encoded image;
a sharpening module configured to perform sharpening on the decoded image;
a detector configured to detect a frequency histogram indicating existing pixels corresponding to each frequency component of the decoded image with respect to the decoded image; and
a controller configured to control effect of the sharpening based on the quantization information such that the effect of the sharpening is reduced as the accuracy decreases, and to control the effect of the sharpening such that the effect of the sharpening is reduced for a decoded image containing a larger number of high-frequency component pixels based on the frequency histogram.
2. The image processing apparatus of claim 1 , wherein the sharpening module comprises:
an unsharp mask configured to enhance a video signal of a predetermined band contained in the decoded image;
a temporary high-resolution image generator configured to generate, from the decoded image, by performing pixel interpolation based on information in adjacent pixels, a temporary high-resolution image with a resolution higher than a resolution of the decoded image;
a difference detector configured to detect a difference between an image generated by the unsharp mask and the temporary high-resolution image;
an adjuster configured to adjust the difference; and
a high-resolution image generator configured to add the difference adjusted by the adjuster to the decoded image to generate a high-resolution image with a resolution higher than the resolution of the decoded image, wherein
the controller is configured to reduce effect of the unsharp mask and the adjuster as the accuracy decreases, and to control the effect of the sharpening as the total effect of the effect of the unsharp mask and the adjuster, such that the effect of the sharpening is reduced.
3. The image processing apparatus of claim 2 , wherein
the unsharp mask and the adjuster are configured to perform coring process to remove noise at or below a predetermined coring level, non-linear process to change characteristics of input and output at a predetermined non-linear level, and gain adjustment, and
the controller is configured to perform at least one of increasing the coring level, reducing the non-linear level, and reducing a gain adjustment amount as the accuracy decreases.
4. The image processing apparatus of claim 1 , wherein the sharpening includes super-resolution enhancement.
5. The image processing apparatus of claim 1 , wherein
the quantization information is a quantization step in a field or a frame, and
the controller is configured to control the effect of the sharpening such that the effect of the sharpening is reduced as the quantization step increases.
6. The image processing apparatus of claim 1 , wherein
the quantization information is an average macroblock quantization scale in a field or a frame, and
the controller is configured to control the effect of the sharpening such that the effect of the sharpening is reduced as the average macroblock quantization scale increases.
7. The image processing apparatus of claim 1 , wherein
the acquisition module is configured to acquire an encoding scheme upon generating the encoded image, and
the controller is configured to control the effect of the sharpening according to the encoding scheme.
8. The image processing apparatus of claim 7 , wherein
the acquisition module is configured to acquire a picture type upon generating the encoded image, and
the controller is configured to control the effect of the sharpening according to the picture type.
9. The image processing apparatus of claim 8 , wherein the controller is configured to control the effect of the sharpening based on one of the quantization information, the frequency histogram, the encoding scheme, and the picture type that reduces the effect more than another.
10. An image processing method applied to an image processing apparatus configured to decode an encoded image and sharpen the image, the image processing method comprising:
a decoder decoding the encoded image to obtain a decoded image;
an acquisition module acquiring quantization information indicating accuracy of quantization upon generating the encoded image;
a sharpening module performing sharpening on the decoded image;
a detector detecting a frequency histogram indicating existing pixels corresponding to each frequency component of the decoded image with respect to the decoded image; and
a controller controlling effect of the sharpening based on the quantization information such that the effect of the sharpening is reduced as the accuracy decreases, and controlling the effect of the sharpening such that the effect of the sharpening is reduced for a decoded image containing a larger number of high-frequency component pixels based on the frequency histogram.