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.
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
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.