Image display method, gradation conversion circuit, and image signal conversion apparatus

• US 6,266,102 B1
• Filed: 09/23/1996
• Issued: 07/24/2001
• Est. Priority Date: 09/25/1995
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Azuma, Takeo, Morimura, Atsushi
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Lo, Linus H.
• Application Number:
  US08/723,877
• Time in Patent Office: 1,765 Days
• Field of Search: 348/625, 348/627, 348/630, 348/671-675, 348/684, 348/252, 382/266, 382/268-269, 382/271-274, 382/22, 382/199, 358/515-522
• US Class Current: 348/671
• CPC Class Codes: H04N 5/202 Gamma control circuits for controlling camera response irrespective of the scene brightness H04N23/82

Abstract

An image display method displays an image by different gradation conversion in every pixel, on the basis of gradation frequency distribution of luminance of pixels near an edge of the image, and counting of gradation frequency of luminance of pixels near the edge is weighted depending on the coordinate values of each pixel so as to eliminate relative contrast drop in the image central part from the image peripheral parts.

Claims

1. An image display method for improving contrast in television images by displaying a television image by different gradation conversion in every pixel comprising the steps of:

extracting an edge of luminance of the image to obtain an edge of the image,

carrying out gradation conversion on the basis of gradation luminance frequency distribution of pixels near the edge of the image,

counting gradation luminance frequency of the pixels near the edge of the image, and

while counting gradation luminance frequency of pixels near the image edge, weighting said counting of gradation luminance frequency depending on the coordinate values of each pixel so as to a eliminate relative contrast drop in a central part of the image with respect to peripheral parts of the image.

6. An image display method of claim 1, wherein said step of extracting an edge is performed by using a one-dimensional filter.

16. An image display method of claim 1, wherein the step of carrying out gradation conversion includes a step of obtaining a gradation conversion table approximated by plural straight lines, thereby reducing operation quantity and circuit scale.

21. An image display method of claim 16, wherein a section length approximated by each straight line is varied depending on the gradation to perform gradation correction and a γ

-correction process at the same time, and thereby gradation conversion depends on characteristics of the display device.

2. An image display method for improving contrast in television images by displaying a television image by different gradation conversion in every pixel comprising the steps of:

extracting an edge of luminance of the image to obtain an edge of the image,

carrying out gradation conversion on the basis of gradation luminance frequency distribution of pixels near the edge of the image,

counting gradation luminance frequency of the pixels near the edge of the image, and

weighting said counting of gradation luminance frequency depending on the gradation so as to perform both a γ

-correction process and the gradation conversion, said γ

-correction process depending on characteristics of a television display device.

7. An image display method of claim 2, wherein said step of extracting an edge is performed by using a one-dimensional filter.

17. An image display method of claim 2, wherein the step of carrying out gradation conversion includes a step of obtaining a gradation conversion table approximated by plural straight lines, thereby reducing operation quantity and circuit scale.

22. An image display method of claim 17, wherein a section length approximated by each straight line is varied depending on the gradation to perform gradation correction and a γ

-correction process at the same time, and thereby gradation conversion depends on characteristics of the display device.

3. An image display method for improving contrast in television images by displaying a television image by different gradation conversion in every pixel comprising the steps of:

extracting an edge of luminance of the image to obtain an edge of the image,

obtaining a gradation conversion table on the basis of luminance gradation frequency distribution of pixels near the edge of the image,

counting luminance gradation frequency of pixels near the edge of the image, and

restricting said counting to pixels other than pixels in the periphery of the image to thereby avoid strangeness in a central part of the image at the time of observation which strangeness is due to affects of luminance frequency of pixels near the edge of peripheral parts of the image.

5. An image display method for as claimed in claim 3, wherein said step of obtaining the gradation conversion table includes the steps of obtaining plural gradation conversion tables by obtaining a gradation conversion table for each of a specific number of representative regions in the image on the basis of the luminance distribution of pixels near the edge, and

executing gradation conversion by interpolating or extrapolating a conversion result given by each gradation conversion table in each representative region for each pixel.

8. An image display method of claim 3, wherein said step of extracting an edge is performed by using a one-dimensional filter.

10. An image display method of claim 5, wherein said step of extracting an edge is performed by using a one-dimensional filter.

11. An image display method of claim 5, wherein the step of calculating of each gradation conversion table in the representative regions is performed in one representative region in one field period, and a gradation conversion table for all representative regions is updated in a specified number of field periods of the representative regions.

12. An image display method of claim 5, wherein a gradation conversion table is calculated for each of four representative regions.

13. An image display method of claim 11, wherein a gradation conversion table is calculated for each of four representative regions.

14. An image display method of claim 5, wherein a gradation conversion table is calculated for each of five representative regions, and a relative contrast drop in a central part of the image with respect to peripheral parts of the image is suppressed, and calculation cost is reduced.

15. An image display method of claim 11, wherein the gradation conversion table is calculated in five representative regions, and a relative contrast drop in a central part of the image with respect to peripheral parts of the image is suppressed, and calculation cost is reduced.

18. An image display method of claim 3, wherein the gradation conversion table is approximated by plural straight lines, thereby reducing operation quantity and circuit scale.

20. An image display method of claim 5, wherein at least one gradation conversion table is approximated by plural straight lines, thereby reducing operation quantity and circuit scale.

23. An image display method of claim 18, wherein a section length approximated by each straight line is varied depending on the gradation to perform gradation correction and a γ

-correction process at the same time, and thereby gradation conversion depends on characteristics of the display device.

25. An image display method of claim 20, wherein a section length approximated by each straight line is varied depending on the gradation to perform gradation correction and a γ

-correction process at the same time, and thereby gradation conversion depends on characteristics of the display device.

4. An image display method for improving contrast in television images by displaying a television image sequence by different gradation conversion in every pixel comprising the steps of:

extracting an edge of luminance of each image to obtain an edge of the image,

obtaining an obtained gradation conversion table for a representative region in the image on the basis of luminance gradation frequency distribution of pixels near an edge of the image for each image, and,

performing weighted-addition of elements in the obtained gradation conversion table with corresponding elements in a previous gradation conversion table for the same representative region to obtain a change limited gradation conversion table having elements that are limited in how they change in time,

wherein strangeness during observation-due to brightness changes in an object in each image in time is decreased.

9. An image display method of claim 4, wherein said step of extracting an edge is performed by using a one-dimensional filter.

19. An image display method of claim 4, wherein each gradation conversion table is approximated by plural straight lines, thereby reducing operation quantity and circuit scale.

24. An image display method of claim 19, wherein a section length approximated by each straight line is varied depending on the gradation to perform gradation correction and a γ

-correction process at the same time, and thereby gradation conversion depends on characteristics of the display device.

26. An image display method comprising the steps of:

generating an illusion image for causing an illusion in an input image from the input image by using a FIR filter in a horizontal direction and an IIR filter in a vertical direction,

converting gradation of the input image to obtain a gradation converted image, and

superimposing the illusion image on the gradation converted image to obtain an image having improved contrast at reduced calculation cost.

27. A gradation conversion circuit for improving contrast in television images, said circuit comprising:

an edge extraction circuit for receiving an image signal representing an input image and extracting an extracted edge of the input image therefrom,

a gradation conversion table calculating circuit for obtaining a plurality gradation conversion tables on the basis of gradation frequency distributions of pixels near the extracted edge,

a memory for storing obtained gradation conversion tables, and

a conversion circuit for performing different gradation conversion of the image signal for every pixel based upon gradation conversion tables stored in the memory,

wherein the gradation conversion table calculating circuit obtains the gradation conversion tables for a plurality of representative window regions which are remote from peripheral parts of the image and, restricts counting to pixels other than pixels in the peripheral parts of the image so as to avoid strangeness in a central part of the image due to affects of gradation frequency of pixels near the edge in peripheral parts of the image.

28. An image signal conversion apparatus comprising:

a gradation conversion circuit of claim 27,

an illusion waveform generating circuit, also receiving the image signal, for generating an illusion image causing an illusion in the input image, and

a superimposing circuit for superimposing an illusion image generated by the illusion waveform generating circuit on output from the gradation conversion circuit.