Note: a Java enabled browser is required to view the sample.

The image below is an 8.5 x 11 page scanned at 200 dpi (black & white). It was saved as a compressed TIFF file (original size 467k, compressed size 125k). The Java viewer in this sample loads the compressed image from the server, then decompresses and scales only the visible portion.  Clicking on the buttons at the bottom of the applet window scales (zooms in and out) the image appropriately. Note that the image is not re-downloaded for each click -- scaling takes place on the client.

A Java enabled browser is required to display the image

The applications for scalable image viewers are countless, from real-estate to medical to legal -- particularly when linked up to an online database of images.

The algorithm used here is called "scale-to-gray". When a black and white image is scaled down, pixels must be thrown away in order to render a smaller image. Scale-to-gray takes a sub-grid of pixels and generates a single gray pixel whose intensity (degree of blackness) is determined by the ratio of black pixels to white pixels. Using this method a type-written sheet of paper can easily be read below 30% original size at 200 dpi.

* Technical note: When we looked at commercially available image viewers to do something similar to what this demo does, we found that they took at least 100k (and sometimes up to 200k) to do it. This little demo is 18k -- The TIFF/JPEG image loader & viewer thread is only about 5k! That's a lot of download time saved.

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Last modified: April 2, 2008