Multimedia Summer Camp Blending pictures and Chromakey

Outline Creating pictures from other pieces Blending pictures Chromakey

Blending pictures Given two pictures, we can create a new pictures by mixing the colors of the pixels to reflect both pictures. When we create collages by copying, any overlap typically means that one picture shows over another. We can blend pictures by multiplying their colors and adding them. This gives us the effect of transparency.

Blending pictures We want to blending the following two pictures

Blending Picture We compute the red, green, and blue for the final pixel by taking 50% of the red, green, and blue of each of the pictures.

Blending pictures

Fade-out Simulation of fade-out feature Let’s say we have two pictures: pict1 and pict2 we can copy pict2 to pict1 multiple times using blend function. At first copy, use 100% color of pict2, and 0% color of pict1 At the second copy, use 95% color of pict2, and 5% color of pict1 At the third copy, use 90% color of pict2, and 10% color of pict1 Repeat this until copy using 0% color of pict2 and 100% color of pict1

Fade-out

Fade-out: Result

Chromakey Chroma key compositing (or chroma keying) is a technique for compositing two images or frames together in which a color (or a small color range) from one image is removed (or made transparent), revealing another image behind it. It is commonly used for weather forecast broadcast, wherein the presenter appears to be standing in front of a large map, but in the studio it is actually a large blue or green background. The meteorologist stands in front of a bluescreen, and then different weather maps are added on those parts in the image where the color is blue.

+ Subtract background (green) from the bride Copy the bride only to the beautiful scene

Chromakey There are more than one way to decide if a pixel’s color “green”. Here we consider a pixel is green if the greenness is greater than both redness and blueness.