iDVD 6 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 TIFF files and JPEG - Quality level 10. I created two new iDVD 6 projects: one with 'Best Quality' and one with 'Best Performance'. Each had a slide show with all 5 TIFF and all 5 JPEG images. I burned the projects to image files and looked at the images with Apple's DVD Player application version 4.0. I made screen grabs of the images with Snapz Pro X version 2.0.2. To make sure the Snapz Pro X screen grab process didn't affect the sharpness, the orginal 640x480 TIF file shown at the left in the comparison below was opened in QuickTime Player 6.5.2 and captured with Snapz Pro X. (Comparing the original TIF file and the screen grab in Photoshop showed no change.) Looking carefully at all the screen grabs, the 320x240 images were (as expected) lower in quality than the 640x480 images. In terms of overall sharpness the 4 largest images were equivalent. I saw no difference between the TIFF files and the JPEG files or between 'Best Quality' and 'Best Performance'. (Since the playing time is very short, I didn't expect to see a difference between 'BP' and' BQ'.) Conclusion: Going to still images larger than 640x480 will gain you no sharpness benefit, but larger images no longer suffer from alaising artifacts afer resizing. Unfortunately, there is still some quality loss as a result of the MPG-2 compression process and the 640x480 (and higher) images were not a 'crisp' as the 640x480 image before MPG-2 compression. The MPG-2 compression process also seems to darken images slightly (see Gray patch test) and this darkening may make the compressed images a little 'muddy'. (See for example the fork at the lower left of each screen grabbed image below.)
Areas from 5120x3840 original images that are sensitive to resampling artifacts.
Diagonal edges		High frequency pattern		High frequency pattern		640x480 source for iDVD 6 test
Click to view large image		Click to view large image		Click to view large image		Click to view large image
Section of original 640x480 TIF image Section of 640x480 image after BQ compression in iDVD 6 Section of 3120x3840 image after BQ compression in iDVD 6 Snapz Pro X screen grab from QuickTime 6.5.2 Player Snapz Pro X screen grab from Apple's DVD Player v 4.0 Snapz Pro X screen grab from Apple's DVD Player v 4.0

Update 2 February 2006: Here is what Apple says about still image size for iDVD 6 slideshows in http://docs.info.apple.com/article.html?path=iDVD/6.0/en/17.html "Preparing images for DVD slideshows":

If you want your images to fit the DVD window exactly, use an image-editing application to crop and resize the images to the following dimensions:

720 x 540 pixels for standard video in NTSC format
854 x 480 pixels for widescreen in NTSC format
768 x 576 pixels for standard video in PAL format
1024 x 576 pixels for widescreen in PAL format

Return to Tutorials index.

23 January 2006, Copyright 2006 by Frederick L. Shippey, Electronic Imaging Consulting