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iDVD Still Image Size Test

I started with a high resolution scan I had shot on 4x5 film several years ago for sharpness testing. It had been scanned on a high-end professional scanner. The file was 5120x3840. I downsized that file in Photoshop (bicubic interpolation) to: 2560x1920, 1280x960, 640x480 and 320x240. I saved these files as JPEG - Quality level 10.

I created a new iDVD project with a slide show and brought in all 5 jpg images. In preview, the 320x240 image was (as expected) lower in quality than the 640x480 image. The 640x480 image looked as expected. The 3 larger images ALL showed alaising artifacts in areas of the image designed to show such problems. I suspect the iDVD preview function (like iMovie) simply resamples the images by throwing away the extra pixels. In terms of overall sharpness the 4 largest images were equivalent.

I burned the DVD on a DVD-RW and looked at the images. The results parallel the preview function with aliasing artifacts in the 3 largest images. I suspect this means that for speed in encoding, iDVD does not recalculate the image downsizing - just throws away the extra pixels.

.Conclusion: going to still images larger than 640x480 does NOT contribute to extra sharpness in iDVD and can lead to alaising artifacts.

Areas from 5120x3840 original images that are sensitive to resampling artifacts. Look at these areas in DVD capture images below.
Diagonal edges	High-frequency pattern	High-frequency pattern
DVD captures — click on the images to view full-size images.
640x480 source for iDVD	DVD capture (320x240 original)	DVD capture (640x480 original)
DVD capture (1280x960 original)	DVD capture (2560x1920 original)	DVD capture (5120x3840 original)

Shooting-Digital.com is the companion site for a new book Shooting Digital: Pro Tips for Taking Great Pictures with Your Digital Camera written by Mikkel Aaland. I was the Technical Editor of the book. Shooting-Digital.com is also an educational site devoted to all aspects of digital imaging. Topics include shooting, acquiring, using and sharing digital images. Check it out!