Rachel Remembers, David Valentine 2010 from The Girl Who Broke the Time Barrier series.
Making images appear to fly is easy. But to make the effect convincing you need to be aware of a few rules about moving in and out of GIF, JPEG or PNG images. Keep in mind that Prezi simulates dimensionality by dynamically resizing your image file to fit the screen no matter how deep (small) you shrink it into the canvas. Prezi will in effect expand it to fill out to your point of view. You need to strike a balance between small length/width and large pixel depth; or "dpi - dots per inch".
If you put identical length/width images say, 4"x6" on an 8.5"x11" canvas that is itself 300dpi, one 4"x6" image however is only 72 dpi while the other 4"x6" image is the same pixel depth as the 8.5"x11" canvas, 300 dpi. When you place the two images side by side the 72 dpi image appears the size of a postage stamp in comparison. Why?
The 72 dpi image is almost 4x smaller than its twin. And since the canvas is 300 dpi the 4"x6" 300 dpi image looks normal. So what does all this mean for zooming in Prezi?
When you are zooming out on an image with relatively low pixel depth its integrity will distort. (See Example 1 below.)
Example 1: Notice the stair-stepped edges of this low dpi image.
The image begins to lose its sharpness and gets fuzzy with stair steps around the edges. .A 300 dpi image can withstand expanded detail without noticeable distortion at even double the size. But that also means its a fatter image that can take longer to upload. The trick is to keep the image small in length/width dimensions. say no more than 5"x7", but higher in pixel depth, say 150 to 200 dpi. Overall your images should be no bigger than 1.5 megabytes to preserve image integrity and smooth playback for zooming. Still with me?
The other thing Prezi does is present all images right side up by default. You can take advantage of this fact by using the Wheel Icon to position your image off center for zooming or spinning into the scene. The Wheel Icon's outer notched circle (Example 2) turns the image clockwise or counterclockwise in increments roughly equivalent to the notches on the circumference of the wheel.
Example 2: The Wheel Icon controls image orientation and size
Sizing the image is controlled by the "+" or "-" symbols; and image placement around the canvas is accomplished with the hand symbol at the center of the Wheel Icon
Let's say you want to create the effect of the "Rachel" image spinning out of the depths to fill the screen right side up. Instead of shrinking the image with the Wheel Icon, use it to turn the image 180 degrees. Use the Canvas Controls ( Example 3 below) to zoom in to the maximum depth of the canvas. The image will automatically shrink. Use the Wheel Icon once again to place the upside down image off left of center.
Example 3: (at the right side of the canvas)
Use the "Paths" option of the circle bubble menu (screen top left in Example 3) and select the "Rachel" image as the next image in the sequence locking in its position on the canvas. Move your mouse to the bottom right of the screen and the "Forward/Reverse" SHOW controls appear. Click "Reverse" to back up to the previous image location in the presentation. Click the "Forward" button to run the show. The current image flips up and off to the right. while the "Rachel" image zoom/spins up from the left.to come to a gradual halt, full size in the center of the screen. I used the same technique to spin into view the my You Tube video on 19th century Sublime American landscape paintings.
The major difference between Prezi and Power Point is Prezi uses non linear motion to enhance relationships between text, images and videos, while Power Point does the same in a linear hierarchical manner. Both have their place. I happen to think Prezi is more fun.
David Valentine
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