Patent Grant
11810496
This application claims the priority benefit of Taiwan application serial no. 111128131, filed on Jul. 27, 2022. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
The invention relates to a display apparatus, and more particularly, to a display apparatus displaying a watermark and an image displaying method thereof.
In confidential documents (such as paper documents or electronic documents), watermarks are usually added to warn users and to leave a clear mark when the confidential documents are copied. However, regarding traditional watermarks, when displayed information is similar to the watermark in hue/grayscale, it may hinder reading and cause discomfort in reading.
The invention is directed to a display apparatus and an image displaying method, where when a confidential document is displayed, human eyes are insensitive to a watermark on the confidential document, but the watermark is obvious to photographic equipment.
The invention provides a display apparatus including a display module and a driving circuit. The driving circuit is coupled to the display module and receives an input image, and the driving circuit determines a watermark area and a non-watermark area of the display module according to watermark information. At least one of the watermark area and the non-watermark area is alternately driven by a first gamma curve and a second gamma curve. A luminance difference percentage between the first gamma curve and the second gamma curve at a same grayscale value between 10% and 90% of a grayscale percentage is between 0.2 and 0.6.
The invention provides an image displaying method of a display apparatus including following steps. An input image is received through a driving circuit of the display apparatus. A watermark area and a non-watermark area of a display module of the display apparatus are determined through the driving circuit according to watermark information. At least one of the watermark area and the non-watermark area is alternately driven by a first gamma curve and a second gamma curve through the driving circuit. A luminance difference percentage between the first gamma curve and the second gamma curve at a same grayscale value between 10% and 90% of a grayscale percentage is between 0.2 and 0.6.
Based on the above, in the display apparatus and the image displaying method according to the embodiments of the invention, at least one of the watermark area and the non-watermark area is driven alternately by the first gamma curve and the second gamma curve. The luminance difference percentage between the first gamma curve and the second gamma curve at the same grayscale value between 10% and 90% of the grayscale percentage is between 0.2 and 0.6. Since human eye perception is equivalent to a luminance integrator, the human eyes may view an image with an intermediate luminance, and photographic equipment with a fast shutter may obviously capture the image. In this way, the watermark to which the human eyes are insensitive but is clear to photographic equipment may be displayed on the display module.
In order for the aforementioned features and advantages of the disclosure to be more comprehensible, several embodiments accompanied with drawings are described in detail as follows.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
It should be noted that although the terms “first”, “second”, “third”, etc. may be used for describing various elements, components, regions, layers and/or portions, the elements, components, regions, layers and/or portions are not limited by these terms. These terms are only used for separating one element, component, region, layer or portion from another element, component, region, layer or portion. Therefore, the following discussed “first element”, “component”, “region”, “layer” or “portion” may be referred to as the second element, component, region, layer or portion without departing from the scope of the invention.
The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. “or” represents “and/or”. The term “and/or” used herein includes any or a combination of one or more of the associated listed items. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used herein, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.
In the embodiment, when the watermark area Rwt is alternately driven by the first gamma curve rA and the second gamma curve rB, the non-watermark area Rnwt may be fixedly driven by another gamma curve (for example, a third gamma curve rC) different from the first gamma curve rA and the second gamma curve rB. Alternatively, when the watermark area Rwt is alternately driven by the first gamma curve rA and the second gamma curve rB, the non-watermark area Rnwt may be alternately driven by the second gamma curve rB and the first gamma curve rA.
Since human eye perception is equivalent to a luminance integrator, i.e., when a high-luminance image and a low-luminance image are switched at a high speed, human eyes may view an image with an intermediate luminance. However, a shutter speed of the photographic equipment is usually faster than a frame update rate of the display apparatus 100, so that the human eyes are not sensitive to a luminance difference between the gamma curves, but the photographic equipment may clearly capture the image. In other words, the human eyes are insensitive to the watermark area Rwt, but for the photographic equipment, the watermark area Rwt is noticeable. In this way, a watermark to which the human eyes are insensitive but is clear to photographic equipment may be displayed on the display module 120.
In the embodiment, the watermark area Rwt has a group formed by first red sub-pixels R1 (i.e., a first red sub-pixel group), a group formed by first green sub-pixels G1 (i.e., a first green sub-pixel group), and a group formed by first blue sub-pixels B1 (i.e., a first blue sub-pixel group), and the non-watermark area Rnwt has a group formed by second red sub-pixels R2 (i.e., a second red sub-pixel group), a group formed by second green sub-pixels G2 (i.e., a second green sub-pixel group), and a group formed by second blue sub-pixels B2 (i.e., a second blue sub-pixel group).
Since the first gamma curve rA and the second gamma curve rB have the luminance difference, if the frame update rate of the display apparatus is too low, the human eyes may feel flickering of a displayed frame. Therefore, in order to reduce the flickering feeling perceived by human eyes, a display time S1 of the first frame N and the second frame N+1 must be less than or equal to 1/80 second (i.e., 12.5 milliseconds (ms)).
In the embodiment of the invention, when both of the watermark area Rwt and the non-watermark area Rnwt are alternately driven by the first gamma curve rA and the second gamma curve rB, during the period of the first frame N, at least the group of the first red sub-pixels R1 in the group of the first red sub-pixels R1, the group of the first green sub-pixels G1, and the group of the first blue sub-pixels B1 is driven by the first gamma curve rA, and at least the group of the second red sub-pixels R2 in the group of the second red sub-pixels R2, the group of the second green sub-pixels G2, and the group of the second blue sub-pixels B2 is driven by the second gamma curve rB. During the period of the second frame N+1 following the first frame N, at least the group of the first red sub-pixels R1 in the group of the first red sub-pixels R1, the group of the first green sub-pixels G1, and the group of the first blue sub-pixels B1 is driven by the second gamma curve rB, and at least the group of the second red sub-pixels R2 in the group of the second red sub-pixels R2, the group of the second green sub-pixels G2, and the group of the second blue sub-pixels B2 is driven by the first gamma curve rA.
In the embodiment of the invention, the watermark area Rwt is alternately driven by the first gamma curve rA and the second gamma curve rB, and the non-watermark area Rnwt is driven by the third gamma curve rC. The third gamma curve rC is between the first gamma curve rA and the second gamma curve rB. Further, during the period of the first frame N, at least the group of the first red sub-pixels R1 in the group of the first red sub-pixels R1, the group of the first green sub-pixels G1, and the group of the first blue sub-pixels B1 is driven by the first gamma curve rA. Moreover, during the period of the second frame N+1 following the period of the first frame N, at least the group of the first red sub-pixels R1 in the group of the first red sub-pixels R1, the group of the first green sub-pixels G1, and the group of the first blue sub-pixels B1 is driven by the second gamma curve rB.
Regarding a driving combination 2, during the period of the first frame N, the group of the first red sub-pixels R1, the group of the first green sub-pixels G1, and the group of the second blue sub-pixels B2 are driven by the first gamma curve rA, and the group of the first blue sub-pixels B1, the group of the second red sub-pixels R2, and the group of the second green sub-pixels G2 are driven by the second gamma curve rB. During the period of the second frame N+1, the group of the first red sub-pixels R1, the group of the first green sub-pixels G1, and the group of the second blue sub-pixels B2 are driven by the second gamma curve rB, and the group of the first blue sub-pixels B1, the group of the second red sub-pixels R2, and the group of the second green sub-pixels G2 are driven by the first gamma curve rA.
Regarding a driving combination 3, during the period of the first frame N, the group of the first red sub-pixels R1, the group of the first blue sub-pixels B1, and the group of the second green sub-pixels G2 are driven by the first gamma curve rA, and the group of the first green sub-pixels G1, the group of the second red sub-pixels R2, and the group of the second blue sub-pixels B2 are driven by the second gamma curve rB. During the period of the second frame N+1, the group of the first red sub-pixels R1, the group of the first blue sub-pixels B1, and the group of the second green sub-pixels G2 are driven by the second gamma curve rB, and the group of the first green sub-pixels G1, the group of the second red sub-pixels R2, and the group of the second blue sub-pixels B2 are driven by the first gamma curve rA.
Regarding a driving combination 4, during the period of the first frame N, the group of the first red sub-pixels R1, the group of the second green sub-pixels G1, and the group of the second blue sub-pixels B2 are driven by the first gamma curve rA, and the group of the first green sub-pixels G1, the group of the first blue sub-pixels B1, and the group of the second red sub-pixels R2 are driven by the second gamma curve rB. During the period of the second frame N+1, the group of the first red sub-pixels R1, the group of the second green sub-pixels G2, and the group of the second blue sub-pixels B2 are driven by the second gamma curve rB, and the group of the first green sub-pixels G1, the group of the first blue sub-pixels B1, and the group of the second red sub-pixels R2 are driven by the first gamma curve rA.
Shown as the luminance difference curve BDF2, between 10% and 90% of the grayscale percentage, a luminance difference percentage of the first gamma curve rA and the third gamma curve rC at a same grayscale value is approximately between 0.3 and 0.4. Shown as the luminance difference curve BDF3, between 10% and 90% of the grayscale percentage, a luminance difference percentage between the second gamma curve rB and the third gamma curve rC at the same grayscale value is approximately between 0.2 and 0.3.
In an embodiment of the invention, between 10% and 90% of the grayscale percentage, the luminance difference percentage between the first gamma curve rA and the third gamma curve rC at the same grayscale value is between 0.2 and 0.6. and the luminance difference percentage between the second gamma curve rB and the third gamma curve rC at the same grayscale value is between 0.2 and 0.6.
Regarding a driving combination 2a, during the period of the first frame N, the group of the first red sub-pixels R1, and the group of the first green sub-pixels G1 are driven by the first gamma curve rA, and the group of the first blue sub-pixels B1 is driven by the second gamma curve rB. During the period of the second frame N+1, the group of the first red sub-pixels R1, and the group of the first green sub-pixels G1 are driven by the second gamma curve rB, and the group of the first blue sub-pixels B1 is driven by the first gamma curve rA. The group of the second red sub-pixels R2, the group of the second green sub-pixels G2, and the group of the second blue sub-pixels B2 are fixedly driven by the third gamma curve rC.
Regarding a driving combination 3a, during the period of the first frame N, the group of the first red sub-pixels R1, and the group of the first blue sub-pixels B1 are driven by the first gamma curve rA, and the group of the first green sub-pixels G1 is driven by the second gamma curve rB. During the period of the second frame N+1, the group of the first red sub-pixels R1, and the group of the first blue sub-pixels B1 are driven by the second gamma curve rB, and the group of the first green sub-pixels G1 is driven by the first gamma curve rA. The group of the second red sub-pixels R2, the group of the second green sub-pixels G2, and the group of the second blue sub-pixels B2 are fixedly driven by the third gamma curve rC.
Regarding a driving combination 4a, during the period of the first frame N, the group of the first red sub-pixels R1 is driven by the first gamma curve rA, and the group of the first green sub-pixels G1, and the group of the first blue sub-pixels B1 are driven by the second gamma curve rB. During the period of the second frame N+1, the group of the first red sub-pixels R1 is driven by the second gamma curve rB, and the group of the first green sub-pixels G1, and the group of the first blue sub-pixels B1 are driven by the first gamma curve rA. The group of the second red sub-pixels R2, the group of the second green sub-pixels G2, and the group of the second blue sub-pixels B2 are fixedly driven by the third gamma curve rC.
Regarding a driving combination 6, during the period of the first frame N, the group of the first red sub-pixels R1 is driven by the first gamma curve rA, the group of the first green sub-pixels G1 is driven by the second gamma curve rB, and the group of the first blue sub-pixels B1 is driven by the third gamma curve rC. During the period of the second frame N+1, the group of the first red sub-pixels R1 is driven by the second gamma curve rB, the group of the first green sub-pixels G1 is driven by the first gamma curve rB, and the group of the first blue sub-pixels B1 is driven by the third gamma curve rA. The group of the second red sub-pixels R2, the group of the second green sub-pixels G2, and the group of the second blue sub-pixels B2 are fixedly driven by the third gamma curve rC.
In the embodiment, the alternating driving combinations 1-4 are split into 1-1 to 4-1 (corresponding to the watermark area Rwt) and 1-2 to 4-2 (corresponding to the non-watermark area Rnwt), and the alternating driving combinations 1-1 to 4-1 may be individually matched with the alternating driving combinations 1-2 to 4-2, where N may be equal to M or M±1. In other words, the alternating driving combinations corresponding to the watermark area Rwt and the non-watermark area Rnwt may be complementary or non-complementary, which is not limited by the embodiment of the invention.
When the alternating driving combination 1-1 is matched with the alternating driving combination 1-2, a flickering value=53.7, a hue difference ΔE=12.12, and the luminance difference is the largest at this time; when the alternating driving combination 1-1 is matched with the alternating driving combination 2-2, the flickering value=42.9, the hue difference ΔE=60.24, and the contrast between the hue difference and the luminance difference is the best, and a degree of flickering is acceptable; when the alternating driving combination 1-1 is matched with the alternating driving combination 3-2, the flickering value=25.2, the hue difference ΔE=53.85, the contrast of the luminance difference (i.e., the flickering) at this time is the lowest, and the hue difference ΔE is the second highest; when the alternating driving combination 1-1 is matched with the alternating driving combination 4-2, the flickering value=37.2, and the hue difference ΔE=33.83. At this time, the flickering is in the middle, and the hue difference ΔE is the smallest. Taking the above combinations as an example, the alternating driving combination 1-1 matched with the alternating driving combination 2-2 have the best contrast value, and the alternating driving combination 1-1 matched with the alternating driving combination 3-2 have the lowest flickering value, so that the configuration of the alternating driving combinations depends on an objective of a circuit design, but the embodiment of the invention is not limited thereto.
Since a threshold of frequency perceived by human eyes is about 60 Hz, when bright and dark change frequency of the watermark area Rwt/non-watermark area Rnwt is greater than or equal to the threshold, the luminance perceived by the human eyes is an average result thereof and there is no flickering phenomenon, so that the differences between the two areas cannot be identified. However, when photographing with the photographic equipment, since a shutter is a fixed value, when a shutter time does not match a bright and dark period of the watermark area Rwt/non-watermark area Rnwt, the bright and dark difference between the watermark area Rwt/non-watermark area Rnwt may be photographed.
Since the threshold of frequency perceived by human eyes is about 60 Hz, when the cycle time of the watermark area Rwt and the non-watermark area Rnwt is less than or equal to 1/60 second, they are invisible to human eyes. In addition, when photographing with the photographic equipment, when the shutter time is the same as or a multiple of the cycle time of the watermark area Rwt and the non-watermark area Rnwt, the difference between the cycle time of the watermark area Rwt and the non-watermark area Rnwt cannot be photographed. For example, in the case where the frame update rate of the display module 120 is 120 Hz, and the cycle time= 1/60 sec, the human eye perception is the average luminance of the watermark area Rwt/non-watermark area Rnwt. As a result, when the shutter of the photographic equipment is set at 1/60 sec (the fastest shutter speed), 1/30 sec, 1/15 see, . . . , the watermark effect cannot be photographed. But the slower the shutter is, the higher an exposure amount is, so that when the image is overexposed, it may also achieve the effect of preventing theft of secrets. Therefore, so that the fastest shutter speed that makes the photographic equipment unable to capture the difference between the two areas is the slower the better in the case that the human eyes cannot perceive.
Since the threshold of frequency perceived by human eyes is about 60 Hz, a/R≤ 1/60 sec & b/R≤ 1/60 sec must be satisfied, where R is a frame update rate of the display module 120. Considering that a cycling frame number a of the watermark area Rwt>a cycling frame number b of the non-watermarking area Rnwt, the frame update rate of the display module 120 is R≥60×a. When the shutter of the photographic equipment is a multiple of a/R, the luminance of the photographed watermark area Rwt is constant; when the shutter of the photographic equipment is a multiple of b/R, the luminance of the photographed non-watermark area Rnwt is constant. Therefore, the conditions that the photographic equipment cannot capture the difference between the two areas are that the shutter speed is the least common multiple of a/R and b/R, and the constant luminance of the two areas are equal. Under multiple frequency combinations of the two areas, the fastest shutter speed of unable to capture the difference of the two areas≥the fastest shutter speed of the individual single frequency.
Considering that the cycling frame number a of the watermark area Rwt>the cycling frame number b of the non-watermarking area Rnwt (for example, the cycling frame number b of the non-watermarking area Rnwt=the cycling frame number a of the watermark area Rwt−1), the maximum value of the least common multiple that may be achieved is: when a=3, the frame update rate required by the display module 120 is 60×3=180 Hz, and the fastest shutter speed is 6/180= 1/30 second; when a=4, the frame update rate required by the display module 120 is 60×4=240 Hz, and the fastest shutter speed is 12/240= 1/20 second; when a=5, the frame update rate required by the display module 120 is 60×5=300 Hz, and the fastest shutter speed is 20/300= 1/20 sec. It may be seen from a relationship between the frame update rate of the display module 120 (proportional to a) and the fastest shutter speed & exposure energy/unit frequency (normalized to 120 Hz), when a is greater than 7, improvement of the fastest shutter speed of the photographic equipment is slowed down, and increase of the exposure energy/unit frequency is slowed down, which is not in line with benefits, so that the cycling frame number a of the watermark area Rwt may be set between 4 and 6.
In the embodiment of the invention, the watermark area Rwt may be divided into more areas. Taking the division of two areas as an example, cycling frame numbers of a first area and a second area of the watermark area Rwt are respectively a1 and a2. Since the threshold of frequency perceived by human eyes is about 60 Hz, a1/R≤ 1/60 sec & a2/R≤ 1/60 sec & b/R≤ 1/60 sec must be satisfied. Considering a1≥a2≥b, the frame update rate of the display module 120 is R>60×a1. When the shutter of the photographic equipment is a multiple of a1/R, the luminance of the first area of the photographed watermark area Rwt is constant; when the shutter of the photographic equipment is a multiple of a2/R, the luminance of the second area of the photographed watermark area Rwt is constant; and when the shutter of the photographic equipment is a multiple of b/R, the luminance of the photographed non-watermark area Rnwt is constant. Therefore, the conditions that the photographic equipment cannot capture the difference of the three areas are that the shutter speed is the least common multiple of a1/R, a2/R and b/R, and the constant luminance of the three areas are equal.
Under multiple frequency combinations of the three areas, the fastest shutter speed of unable to capture the difference of the three areas≥the fastest shutter speed of the individual single frequency. Considering that a1≥a2≥b, when a=4, the least common multiple is 12, i.e., dividing into three areas and dividing into two areas (a=4) have the same benefits; when a1≥5, the least common multiple is 60, compared with the condition of dividing into two areas (a=5), dividing into three areas may greatly reduce the fastest shutter speed and increase the exposure energy/unit frequency. Therefore, when the watermark area Rwt is divided into more areas, the increase of the cycling frame number may greatly reduce the fastest shutter speed and increase the exposure energy/unit frequency.
In summary, in the display apparatus and the image displaying method according to the embodiments of the invention, at least one of the watermark area and the non-watermark area is driven alternately by the first gamma curve and the second gamma curve. The luminance difference percentage between the first gamma curve and the second gamma curve at the same grayscale value between 10% and 90% of the grayscale percentage is between 0.2 and 0.6. Since human eye perception is equivalent to the luminance integrator, the human eyes may view an image with an intermediate luminance, and photographic equipment with a fast shutter may obviously capture the image. In this way, the watermark to which the human eyes are insensitive but is clear to photographic equipment may be displayed on the display module 120.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention covers modifications and variations provided they fall within the scope of the following claims and their equivalents.
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