VLIV, The Very Large Image Viewer for Windows

In my spare time, I have coded VLIV as an exercise in programming Windows.
The idea was to create a minimal viewer for very large TIFF (tiled).

It uses a very simple idea : only visible tiles are loaded in memory, as soon as a tile is no more visible, it is discarded.

This works very well, because in no more than the visible tiles have to be loaded, so that panning is fast, and zooming also.

VLIV has no advanced features you could think of, such as a caching, or loading tiles in advance, mostly because on local files, performance is already very good.

TIFF has built in support for tiles, but VLIV also creates Virtual Tiles for some formats that have no native tile support (such as PPM or BMP). It manages only parts of the images instead of loading completely the image, even if the format does not support natively tiling.

It also uses a special capability of the JPEG format to allow instant unzooming.

Here is a screendump of VLIV in action on a 86400x43200 pixels image:



VLIV is Shareware, and the price is 10$ (or Euros). I give instructions on VLIV site to build the shown image.

How many people have 4 gigabytes of memory ?

While most computers can display images taken from a digital camera, a special care is required to allow display of gigapixel images. Let’s see why.

Usually, a pixel takes 3 bytes of memory, one for each Red, Green and Blue component. Standard image viewers are loading the image completely in memory to display it, even if visible area of your image is only 1280x1024 pixels because of your physical screen size.

Best digital camera have a 12 Megapixel sensor, let’s say 4000x3000 pixels. This makes 36 000 000 bytes required for storing in memory the image. This is possible on any machine available now.

Let’s now take a gigapixel image at 40000x30000 pixels. This makes 100 times more memory, peaking at 3 600 000 000 bytes, that is 3.6 gigabytes.

Unless you have actually 4 Gigabytes of memory and your OS allows a chunk of this size to be allocated, then there is no way you can display the image on your machine, standard software will either crash or not allow image loading or will take forever to load.

Unless you use some clever way of organizing the image data and you have a dedicated viewer that knows how to handle this specific organization.

Next post will discuss this organization, usually called pyramidal tiling.