Ulead 1.0 - Manual (Page 125)

SpruceUp User’s Guide 6—17
Square Pixel Issues
What is a "Square Pixel"?
The term "Square Pixel" actually refers to the distance from a pixel to its neighbors
horizontally and vertically. With a square pixel, the distance is the same in both directions.
This distance is a function of the sampling rates, both horizontal and vertical, and the aspect
ratio it will be displayed in. Given the right aspect ratio, virtually any combination of
horizontal and vertical sampling could produce square pixels.
Computer graphics programs are optimized to work with square pixels – when you draw a
square it uses the same number of pixels to make all four of its sides and looks like a
square on the display.
Unfortunately, video is different.
Video Pixels
Standard video uses a 4:3 aspect ratio. No matter the size of the display, the height is
always 75% of the width. This is true for both NTSC where there are 525 lines in each frame
(480 active with DVDs), and PAL, which has 625 lines per frame (576 active). Both
standards also have 720 pixels per line when converted to MPEG.
An imaginary standard that used the same 720 pixels per line with 540 lines would fit the
4:3 aspect ratio perfectly using square pixels. For NTSC with 480 lines, the lines must be
spaced a bit farther apart to fill the same area, resulting in rectangular pixels. For PAL with
576 lines, they must be squeezed together a bit to fit.
SpruceUp uses square pixels in the Work Area when authoring, and forces the pixels to fit a
640 by 480 (4:3 ratio) window in simulation. For this reason, when authoring, the Work
Area is not 4:3, but the simulate mode is.
What Does This Really Mean?
If you create a square button in the authoring mode and then simulate the title, it will no
longer be square. On NTSC systems it appears a bit narrow, and on PAL systems it is a bit
short. The differences are not large, and are typically not noticeable, but they need to be
taken into account when creating your menus.