Dynamic softclipping of video levels

Abstract

The present invention relates to a method for improvement of contrast in an image shown on a display having a range of displayable video levels. The method comprises providing input video levels representing the image, said levels being within said displayable range; providing a transfer function (120, 121) having a slope greater than one everywhere in a gain region (130) of said displayable range, and a slope greater than zero and less than one everywhere in a softclip region (131) of said displayable range, said regions (130, 131) meeting at a threshold level (125), the transfer function (120, 121) being adapted to transfer any input video level within said displayable range to an output level within displayable said range; and transforming said input levels into output levels within said range, using the transfer function (120, 121). According to the invention, instead of 'hardclipping' there is a 'softclipping' of levels. Hence, compared to conventional methods, a higher gain may be used. In practical situations, the gain applied in the gain region typically may be up to 4.

Description

technical field [0001] The invention relates to a method for improving the contrast of an image displayed on a display by using a gain. Background technique [0002] One of the ways to increase the contrast of an image displayed on a display such as an LCD or plasma display is to apply a gain (>1) to the image data. For example, if the pixels in an image have almost the same brightness value, such as if the image has many dark areas, you would want to use this method in that image. Gain results in higher video levels (ie typically brighter images) and wider distribution of video levels (ie increased perceived contrast). [0003] Another situation where you might want to apply gain is when using a dynamic backlight algorithm (DBL) in an LCD. In LCDs, dark scenes appear "blueish" due to backlight leakage through the LCD panel, the solution to this is to reduce the backlight brightness in such scenes by using DBL. When reducing the backlight brightness, video gain is requ...

AI Technical Summary

Problems solved by technology

[0013] However, although the method of EP0963111A1 can be used to improve the contrast between darker and brighter areas, it is only able to provide relatively small gains and thus small contrast improvements, especially in the case of scenes with a large number of dark samples, e.g. dark pixels dominating Down

This for example makes it unsuitable for use in LCDs in connection with dynamic backlighting

[0014] Also, while the method of EP0963111A1 can be used to prevent rigid clipping in bright regions by using "unity gain" in the second stage, any gain applied in the first stage can result in the need for rigid clipping in dark regions, i.e. Since the transfer function can produce values ​​below 0 (black), the output may need to "clip" these values ​​to black, so there will be a loss of contrast in dark areas

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