File format

We use only losseless compression for all our images. We decided to distribute all our images in a PNG graphic format because it offers the most benefits from all other formats:

It is lossless and offers best possible quality
It use good compression ratio
It is royalty-free format! (More and more important these days)
All current applications supports it
It offers 32 bit version with Alpha channel
All current browsers can display it directly

Sizes and pixel aspect

We use the most universal size that is a best suited for DVD menus and video and it can be easy manipulated in any image editing application
720 x 540 (1:1 pixel aspect)

We use this size because:

It is suitable for both NTSC and PAL
Square pixels keep things simple during editing on PC (The 0.9091 aspect for NTSC and 1.0926 for PAL makes things only unnecessary complicated)
During editing on PC the circle on screen will be a circle on DVD or video which is not true for non-square sized pixels
You can easily resize it to 720x480 NTSC or 720x576 PAL in any application without introducing artefacts

Why not use higher size? Don't let the pixel size fool you - this is not the same as if you compare it with a picture from digital camera of the same pixels size. A digital film or video cannot reproduce small details because one pixel is in reality a cluster of many pixels so the resolution of digital camera is relatively low (that's why you need many megapixels). Our images are created as pure digital files with double precision and so they have comparable resolution and quality to images of four times the pixel amount. Higher pixel images could in fact bring more troubles than benefits for DVD or video - the down-scaling algorithm in your image or video editing application can easily produce unwanted errors such as moire patterns or blurring.

No Compression artefacts

We strictly and proudly go for zero compression artefacts. During designing process we always use lossless compression and we never use any source images that may exhibit them. Compression artefacts are nasty things because a further mpeg2 compression for DVD or encoding or rendering it to a DV 25 tends to amplify them.