Exploring Video Formats

Because of the variety of video-editing systems on the market, each has its own proprietary format for preserving timeline edits and special-effects information so the user can save and continue to edit their footage at a later date. For example, Adobe Premiere uses a .ppj file extension, NewTek s Video Toaster uses .rtv files, Video Delux uses .mtv , and Adobe After Effects uses .aep , to name a few. There are some universal formats such as Targa ( .tga ), MPEG ( .mpg ), and AVI. Most editing programs will support those formats. Some will use their own codecs (compression- decompression schemes) ”for example, Apple s QuickTime or Microsoft s AVI. Some, but not all, formats will incorporate codecs to compress and decompress the video images and sound. This process reduces storage requirements and data rates, enabling you to save the project for distribution via the Web, CDs, or DVDs. Almost all video-editing systems will enable you to export to various formats.

All video editing will use interlaced or (on occasion) noninterlaced formats. Interlaced files record video imagery in even and odd horizontal fields of data that each display half of the image frame (see Figure 27.1). The purpose of separating this data into even and odd fields is simple: it s a bandwidth issue. Video images are sliced up into fields for the same reason that Web designers slice up a single image for preparation of a website ” because smaller amounts of data will transfer faster and more efficiently than larger ones. Also, just like Web graphics, the resolution is 72 ppi (pixels per inch). Be aware that unless traditional film was scanned in at user-defined settings, it is conventional for any files imported from any digital and/or video camera to be at a resolution of 72 ppi with the width and height changing accordingly .

Figure 27.1: (left) A noninterlaced image, and (right) an example of interlaced technology

The larger alternative is noninterlaced, which is composed of one complete image per frame and takes up a greater amount of bandwidth. This improves the visual quality of each frame. However, not all video-editing programs will recognize and edit noninterlaced file formats. Recently, Avid, Apple s Final Cut Pro, and Video Toaster 3 software and systems are a few that will edit this format. All software packages will edit the standard interlaced frames .

Understanding Pixels

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The more pixels that are added to a file, the higher the resolution of the image. In other words, 150 pixels per inch is twice the resolution and file size of the same image that is 72 pixels per inch. So what does this have to do with video aspect ratios? Most of us have been working with square pixels, but now Adobe has given us the ability to format our images for rectangular video formats. Let s discover how this works.

Figure 27.2 is 5 ² ² —5 ² ² with a resolution of 72 ppi that is completely square and is measured by five square objects of equal dimensions. For this example, consider the small square objects your pixels. Keep in mind that the file size is 379 KB.

Figure 27.2: Image at square pixel dimensions

Now choose Image ’ Pixel Aspect Ratio and view the variety of square and rectangular pixel aspect ratios (see Figure 27.3). Choose D1/DV PAL Widescreen 1.066 for an extreme view of the original. Look what happened (see Figure 27.4)! The once square file is now stretched ”but the file size is still 379 KB! The reason is simple: You have not added any more or taken away any less pixel information in this file. You simply took the existing square formatted pixels and stretched them to be rectangular; thus the file size remains the same but formatted to video dimensions of your preference.

Figure 27.3: The Pixel Aspect Ratio submenu

Figure 27.4: The image at rectangular pixel dimensions

So what does this mean to the digital video artist? Understand that anything that is scanned into your computer will take on the square pixel format. That means any flatbed, film, or drum scanner will produce square pixels. However, digital video cameras that produce digital footage natively will produce rectangular pixels. Now Photoshop CS can accommodate the video format without adding more pixel information.

Understanding Video Aspect Ratio

Making films or video is an art. The ideal situation would be to choose a format ratio that is best for setting the mood of film. However, sometimes formats are chosen out of the sole necessity to cut costs.

Films can be shot in frame aspect ratios of 4:3 (4 width by 3 height) or widescreen (anamorphic) video formats of 16:9 (16 width by 9 height) to gain a more cinematic feel (see Figure 27.5). Some of the newer formats include HDTV (high-definition television) for both NTSC (American formats) and PAL (European video format standard).

Figure 27.5: The smaller box has a 4:3 aspect ratio; the larger one is 16:9.

Table 27.1 shows the dimensions of several video aspect ratios as well as some of the presets Photoshop allows when you create a new file. And don t forget that the resolution of the video formats are screen resolution at 72 ppi. This means that the dimensions of your file will change in width and height as needed while the resolution will remain at 72 ppi. In essence, you are working with the normal resolution of your monitor of 72 pixels per inch.

Table 27.1: Dimensions of Selected Video Formats

FORMAT	SQUARE PIXEL PHOTOSHOP	RECTANGULAR PIXEL
NTSC 4:3 analog	640 —480	N/A
NTSC 4:3 digital	720 —534	720 —480
NTSC 16:9 anamorphic	864 —540	720 —480
PAL 4:3	768 —576	720 —576
PAL D1 DV Widescreen (with Guides)	720 —576
PAL D1 DV Widescreen (with Guides)	768 —576
HDTV (with Guides)	1280 —720
HDTV (with Guides)	1920 —1080