Sunday, October 23, 2005

A Cure for Aspect Ratio Madness

Some time ago I wrote about Aspect Ratio Madness, the problem that every device for displaying pictures and video has a different aspect ratio. In that entry I promised to suggest a cure, so here it is. We now live in the digital age and as you know metadata is the cure for all problems digital. For digital images there is already a standard for the metadata that goes with the picture.

The idea is very simple. My proposal is that we include metadata with the image about how to crop it and the display device, knowing its aspect ratio, uses that metadata to display the image. The new metadata is a minimum bounding box for display of the image.

The minimum bounding box is the part of the image that must be displayed when it is presented. The maximum bounding box is the picture itself. So when we come to edit a picture we crop the picture to the maximum that can be rescued from the image and we also crop the an interior section of the image that is the part that we really want to see. This inner crop is saved in the metadata.

When we go to display the image, either by printing it on a printer, or showing it on a computer slide show or when rendering a slide show movie, the display device decides how much of the picture to show, always including all of the minimum bounding box and then filling the display out as needed with rest of the image to fill the frame. If there is no image to show the display device uses its default, which is black bars for screen and blank (white) for printing.

The display device also knows whether it can rotate the image for display. When an image has a minimum bounding box that is taller that it is wide, a printer can rotate the image by 90 degrees, while a computer display or movie render cannot rotate the picture.

This works for still images because there is metadata that goes with each image. For video, there is metadata for the whole movie, however there is no metadata for each frame or shot. If we add the metadata for each shot in a movie, we can create video that can be shown on any display, 16x9, 4x3, or whatever and still look correct.

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