Process and apparatus for blending images
A process and circuit for blending a foreground image (B) with a background image (A), said foreground and background images being arranged in pixels and having color representations (R, G, B). The foreground foreground image (A) has a transparency parameter (T(x,y)) in accordance with a so-called alpha plane representative of the transparency profile to apply to the foreground image. The process involves the steps of: -applying a dithering method on said alpha plane in order to convert said transparency parameter (T) into a one-bit transparency parameter (T′); -use said one-bit transparency parameter (T′) for controlling a multiplexing unit having two inputs respectively receiving the foreground image (A) and the background image (B). In one embodiment, the one-bit transparency parameter T′ into the two extreme values of a range of continuous values, for instance coded on 8 bits. The process then applies a four-pixel interpolation method to the foreground image (A) for the purpose of creating a five level transparency parameter in the blending process, and then uses the five level transparency parameter for controlling a multiplexing circuit for the purpose of achieving blending of the foreground image with the background image.
1. A method of blending a foreground image with a background image, said foreground and background images being arranged in pixels and having color representations defining the color of each pixel, the foreground image having further an N-bit transparency parameter associated with each pixel, the transparency parameters defining an alpha plane representative of a transparency to apply to the foreground image, the method comprising, for each pixel:
applying a dithering operation on the alpha plane to convert the N-bit transparency parameter into a one-bit transparency parameter;
multiplexing between the foreground image and the background image using the one-bit transparency parameter;
converting the one-bit transparency parameter into one of two extreme values of a predetermined range of continuous values;
applying a four-pixel interpolation method to the foreground image to create a five level transparency parameter; and
multiplexing predetermined fractional mixtures of the foreground image and the background image using the five level transparency parameter.
2. The method of claim 1 wherein the predetermined range of continuous values is represented by an 8-bit value, and wherein the one-bit transparency parameter is converted into one of hexadecimal values 00 and FF.
3. The method of claim 1 wherein the dithering operation comprises a Floyd Steinberg dithering operation.
4. The method of claim 1 wherein the dithering operation comprises one of Halftoning and dithered order operations.
5. A circuit operative to blending a foreground image with a background image, the foreground and background images being arranged in pixels and having color representations defining the color of said pixel, the foreground image further having an N-bit transparency parameter associated with each pixel, the transparency parameters defining an alpha plane representative of a transparency to apply to the foreground image, the circuit comprising, for one or more pixels:
a dithering circuit operative to apply a dithering operation on the alpha plane in order to convert the N-bit transparency parameter into a one-bit transparency parameter;
a multiplexer operative to select the color components from the background image or the foreground image, in response to the one-bit transparency parameter value;
a converter operative to convert the one-bit transparency parameter into one of two extreme values of a predetermined range of continuous values;
an interpolator operative to perform a four-pixel interpolation method to the foreground image to create a five level transparency parameter; and
a multiplexer operative to select predetermined fractional mixtures of the foreground image and the background image using the five level transparency parameter.
6. The circuit of claim 5 wherein the predetermined range of continuous values is represented by an 8-bit value, and wherein the converter is operative to convert the one-bit transparency parameter into one of the hexadecimal values 00 and FF.
7. The circuit of claim 5 wherein the dithering circuit is operative to apply a Floyd Steinberg dithering operation on the alpha plane.
8. The circuit of claim 5 wherein the dithering circuit is operative to apply one of a Halftoning and dithered order dithering operation on the alpha plane.
9. A portable communication device, comprising:
a display operative to output a blended foreground image and background image, the foreground and background images being arranged in pixels and having color representations defining the color of said pixel, the foreground image further having an N-bit transparency parameter associated with each pixel, the transparency parameters defining an alpha plane representative of a transparency to apply to the foreground image; and
a blending circuit performing a blending operation for output by the display, the blending circuit comprising, for one or more pixels,
a dithering circuit operative to apply a dithering operation on the alpha plane in order to convert the N-bit transparency parameter into a one-bit transparency parameter;
a multiplexer operative to select the color components from the background image or the foreground image, in response to the one-bit transparency parameter value;
a converter operative to convert the one-bit transparency parameter into one of two extreme values of a predetermined range of continuous values;
an interpolator operative to perform a four-pixel interpolation method to the foreground image to create a five level transparency parameter; and
a multiplexer operative to select predetermined fractional mixtures of the foreground image and the background image using the five level transparency parameter.