Creating text & still images for DV & DVD by Matt Ottewill

When creating images in an image editing application, such as Photoshop, some simple rules should be followed to ensure they are legible ..

Pixel aspect ratio (screen size)

Square & non-square pixels

This is an absolute pain but you need to know that ...

• Computers use square pixels
• Standard definition (SD)video uses non-square rectangular pixels
• High definition (HD) video use square pixels

Therefore ... if you are creating still image artwork (such as title captions), in an image editing application like Photoshop, for an SD project you must take this difference into account.

If you are working in HD you don't need to worry about any of the following advice. Just use the same pixel aspect ratio for your stills as your video.

Still images for SD video

Complete the following 5 steps ...

1) In Photoshop create a frame size (canvas size) that's the square equivalent of the video frame size you're using. Thus if you're using DV-PAL (non square size of 720 x 576) video clips, your still image should have a (square) pixel size of 768 x 576.

2) Create your image.

3) Save the image file.

4) Rescale the image from the square size to the non square equivalent (it will look distorted).

5) Save the image as a copy under a different name and import it into Final Cut Pro (or whatever editing software you are using). It will look distorted on your computer screen but correct on a TV.

Video still images for computer screens (QuickTime, AVIs etc)

If you are creating video which will be viewed on a computer screen then you can happily create your still images at the square equivalent video aspect ratio of the source video clips and you do not need to rescale them.

Image resolution

As a general rule you should stick to 72ppi (pixels per inch) resolution for your images.

Apple's DVD Studio Pro

However, Apple's DVD Studio Pro lets you import Photoshop files at higher resolutions. So if you think your menus and captions need it, use 300ppi. NOTE: Images imported in any other format (eg PICT) must be at 72ppi.

Title safe area

Non flat screen TVs distort the image towards the edge of the screen. To ensure all your titles are legible you should keep them within the so called "title safe area" of the screen.

The title safe area is a rectangle with its edges 10% in from the left, top, right and bottom edges of the frame.

If you are producing a still image in Photoshop for PAL video (768 x 576 pixels) position vertical guides 77 pixels from the left and right edges, and horizontal guides 56 pixels from the top and bottom edges and create all your text elements within the rectangle they create.

When you rescale the image prior to importing into your DV or DVD authoring program your text will be legible and undistorted.

Broadcast colours

TVs cannot reproduce the range of colours which computer screens can. If you juxtapose saturated colours they will bleed into each other making your image look indistinct.

In Photoshop you can do the following ...

• Apply the NTCS colour safe filter to all layers (Filters>Video>NTSC).

• In Levels, adjust black output to 15 & white to 235 for all layers.

Ensure you apply a colour safe filter as the last step before saving your image, otherwise subsequent alterations may introduce non-colour safe colours back into the image.

Eliminating flicker

Interlacing (to do with the way that TV pictures are composed of lines) may cause thin and serifed text and thin horizontal lines to flicker. To avoid flicker try the following ...

• Do not use horizontal lines (or picture elements) thinner than 3 pixels. This applies to image elements and text.

• Avoid text/fonts with delicate serifs.

• If you must use delicate text try ...
  ... copy the darkest channel to make an alpha channel (created to add transparency) and apply a motion blur with a direction of -90 at a distance of 1 or 2 pixels ... or
  ... apply a drop shadow to the text

Flattening Photoshop files

DVD Studio Pro, Final Cut Pro and other video programs cannot work with layer styles, effects layers and adjustment layers so you will need to render or flatten or merge these elements into pixel layers.