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When you watch TV, why doesn’t the picture always fit the screen, and what’s up with those black bars? In this lesson students learn about aspect ratios in TV and film, and how the process of “letterboxing” affects the final image. They’ll also use proportions to find out what happens when you change the ratio on a TV.

If the picture doesn’t fill the screen, should we use the remote to zoom in, and what is lost when we do? Let’s find out.

### Students will

• Understand that media are filmed using different aspect ratios, e.g. 4:3 (“standard”) and 16:9 (“widescreen”)
• Explain that an aspect ratio of 4:3 means that for every four units of width, there are three units of height
• Use aspect ratios to calculate the dimensions of different screens
• Understand why a movie broadcast in 4:3 will not fill a 16:9 screen, and vice-versa
• For both "letterbox" and "zoom" images, calculate the dimensions of the resulting image, including how much empty space there will be (broadcast) or how much of the original image will be cropped (zoom)
• Discuss advantages & disadvantages of letterboxing

### Before you begin

Students should be able to explain the geometric meaning of a ratio of lengths such as 4:3, and use them to reason proportionally. Students should be able to calculate the percent change in area of a rectangle.