Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
1998-09-22
2002-03-12
Brier, Jeffery (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C345S604000
Reexamination Certificate
active
06356277
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a YUV-RGB digital conversion circuit which converts a digital luminance signal Y and digital color-difference signals U and V into digital color signals R, G, and B, an image display apparatus using the same, and an electronic apparatus using the image display apparatus.
2. Description of Related Art
As an electronic apparatus using an image display apparatus, for example, a projector will be given as an example.
A liquid-crystal display apparatus of this projector includes a liquid-crystal panel having a liquid crystal sealed between a pair of substrates, a signal processing circuit for performing signal processing, such as gamma correction or polarity inversion, suitable for driving the liquid-crystal panel, on an input RGB signal, and a driving circuit for driving the liquid-crystal panel on the basis of an output of this signal processing circuit.
Here, because of a demand for a liquid-crystal display apparatus with a smaller size, the signal processing circuit must be formed into an IC. Therefore, a digital RGB signal must be provided to the signal processing circuit of the liquid-crystal display apparatus.
The RGB signal provided to this liquid-crystal display apparatus is output from the control board of the main unit of the projector. This control board is provided with a YUV-RGB conversion circuit for converting a luminance signal Y and color-difference signals U and V into RGB signals. Here, in the control board, it is necessary to perform various processing on the RGB signal, and since a memory, such as a VRAM, is used for this processing, digital processing is suitable for the signal processing by the control board. If YUV-RGB conversion by the YUV-RGB conversion circuit is performed digitally, the efficiency is high.
The YUV signal and the RGB signal have the following relationship when each signal is assumed to be of 8 bits (=256 gradations):
R=Y+(V−128)×1.371 (1)
G=Y−(V−128)×0.337−(U−128)×0.698 (2)
B=Y+(U−128)×1.733 (3)
The value of 128, which is subtracted from the color-difference signals U or V, is the middle value of 256 gradations and differs depending upon the total number of gradations. The reason why the middle value of the total gradation value is subtracted from the color-difference signals U and V as described above is that each coefficient shown in equations (1) to (3) must be multiplied by a color-difference signal which becomes positive or negative, assuming to be zero when it has the middle value of the full gradation value.
Here, each of the coefficients multiplied by (V−128) and (U−128) includes a decimal, such as 1.371, 0.337, 0.698, or 1.733.
To realize a product of such decimals by logic, a method is known in which this decimal is expanded into the sum of 2
−n
(n is a natural number) and computed. For example, (V−128)×0.5=(V−128)×2
−1
can be determined by shifting the digital value of(V−128) by one bit to the lower order. Similarly, (V−128)×2
−n
can be computed easily for each coefficient (−n) by shifting the digital value of (V−128) by n bits to the lower order.
Each of the above-described coefficients is expanded to the sum of 2
−n
as described below.
1.371≈2
0
+2
−2
+2
−4
+2
−5
+2
−6
+2
−7
+2
−9
+2
−10
+2
−11
+2
−12
+2
−13
+2
−16
+ . . .
0.337≈2
−2
+2
−4
+2
−6
+2
−7
+2
−10
+2
−14
+2
−16
+2
−17
+2
−19
+2
−24
+2
−25
+ . . .
0.698≈2
−1
+2
−3
+2
−4
+2
−7
+2
−9
+2
−11
+2
−12
+2
−19
+2
−25
+2
−26
+2
−30
+ . . .
1.733≈2
0
+2
−1
+2
−3
+2
−4
+2
−5
+2
−7
+2
−8
+2
−9
+2
−11
+2
−14
+2
−16
+2
−17
+ . . .
Regarding the above-described coefficients, only approximated coefficients can be used as long as the number of expansion terms is finite. Here, if this coefficient is expanded to multiple terms, a more accurate value can be used, but the scale of the circuit becomes large. On the other hand, if the number of expansion terms is decreased too much in order to reduce the scale of the circuit, the computation error becomes larger. As described above, the number of expansion terms of the coefficient must be determined by taking both the scale of the circuit and the computation error into consideration.
Next, the scale of the computation circuit is considered after the number of expansion terms is determined. In the case where, for example, the coefficient 1.371 is expanded to seven terms and approximated in equation (1) described above, if each of these terms is added in sequence, six adders are required, and the scale of the circuit increases. Also, if, for example, the data is of 8 bits, the 2
0
term of the highest order requires 8 bits for only the integer part, and the 2
−8
term of the lowest order requires 8 bits for only the decimal part. During the computation process, 16 bits are required for the total of the integer part and the decimal part, and this causes the scale of the circuit to increase.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a YUV-RGB digital conversion circuit capable of reducing the scale of a circuit by decreasing a number of adders for adding the terms such that a coefficient including a decimal to be multiplied by a digital color-difference signal is approximately expanded to a finite number of 2
−n
terms in each conversion section for converting a digital YUV signal to a digital RGB signal, and an image display apparatus and an electronic apparatus using the YUV-RGB digital conversion circuit.
Another object of the present invention is to provide a YUV-RGB digital conversion circuit capable of reducing the scale of a circuit by truncating unnecessary bits in a computation process in which each term of 2
−n
is added together, and an image display apparatus and an electronic apparatus using the same.
Still another object of the present invention is to provide a YUV-RGB digital conversion circuit capable of outputting an RGB signal such that the display is not inverted even if there is an input value other than a theoretical specified value, and an image display apparatus and an electronic apparatus using the same.
The invention is characterized in that, a YUV-RGB digital conversion circuit for converting a digital luminance signal Y and digital color-difference signals U and V into digital color signals R, G, and B includes a YV-R conversion section for converting a digital luminance signal Y and a digital color-difference signal V into a color signal R,
a YUV-G conversion section for converting a digital luminance signal Y and digital color-difference signals U and V into a color signal G, and
a YU-B conversion section for converting a digital luminance signal Y and a digital color-difference signal U into a color signal B,
each conversion section includes a plurality of bit-shift circuits, provided in each stage, for outputting an input signal×2
−k
(k is a natural number such that k≦n) by bit-shifting an input signal by one or a plurality of bit-shifting in order to add the terms such that a coefficient including a decimal multiplied by a digital color-difference signal is approximately expanded to a finite number of terms of 2
−n
(n is a natural number); and
a plurality of adders, provided in each stage, for performing addition of the terms of two sets of an input signal×2
−k
, whose value of the multiplier k
Konishi Masaniri
Yajima Kenichiro
Brier Jeffery
Oliff & Berridg,e PLC
Seiko Epson Corporation
Yang Ryan
LandOfFree
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