Apple MA261Z/A User Manual - Page 768

Selecting Fonts and Creating Line Art for Video When creating line art or selecting a font to use for a broadcast video image, you should avoid creating horizontal single-pixel lines, or using fonts that are too thin. Because video is interlaced, horizontal lines that have a height of a single pixel will flicker as the field in which they appear alternates on and off. This causes a distracting shimmering in your graphics, with the shimmering becoming more pronounced the closer thin areas in your image are to horizontal. For more information, see "Installing and Choosing Fonts" on page 856. Flickering horizontal lines can be mitigated by adding a bit of blur or anti-aliasing to your image, causing the lines to subtly spread out over more than one line. However, the best thing to do is to avoid single-pixel lines altogether when creating graphics for broadcast. Scaling Images and Video Clips to Match a Sequence Whenever you edit a still image clip into a sequence, Final Cut Express HD compares and automatically adjusts the following properties of image and sequence: Â Horizontal and vertical dimensions: If the still image dimensions are larger than the sequence dimensions, the still image is scaled to fit in both dimensions (without distorting the image). This means that you always see the entire still image within the frame of the sequence. If the graphic has smaller dimensions than the sequence, the graphic is not scaled. This is because scaling images beyond 100 percent reduces the quality (pixels would be magnified, which would create blocky artifacts in the image). Final Cut Express HD avoids automatically scaling clips beyond 100 percent. Â Pixel aspect ratio: If the still image pixel aspect ratio is different from the sequence pixel aspect ratio, Final Cut Express HD adjusts the still image clip's Aspect Ratio parameter (located in the Distort parameter of the clip's motion parameters). This compensates for mismatched pixel aspect ratios between the still image and the sequence. The result is that the clip does not appear distorted simply because it has a different pixel aspect ratio. Without this automatic compensation, you would have to manually calculate how much to compensate for mismatched pixel aspect ratios. For more information, see "Controls in the Motion Tab" on page 692. If you want to zoom in and out on an image, such as a scanned map or photograph, you should use an image with higher resolution than the sequence. The more high resolution it is, the less likely you will need to scale more than 100 percent to show details. Scaling video and still images more than 100 percent creates artifacts: Individual pixels become noticeable, causing a "stair-stepping" artifact on high-contrast diagonal lines. Note: You can add the illusion of camera motion to still images, as is often done in documentaries, by subtly keyframing the Scale setting (for zooming) as well as movement of the image within the frame (center, anchor, and rotation parameters). See "Example: Adding Camera Motion to Still Images" on page 770 for details. 768 Part IX Effects