To determine how much change may be introduced in the color and density values of images as they pass through the iLife applications chain, I spent several hours experimenting.

I started with a DV color bar clip created in Adobe's Premiere 6.5 which I 'ran' through iMovie 4 and then used the iMovie 4 output in iDVD 4 and Toast 6. I did the same thing with the original bar clip and iMovie H, iDVD 5 and Toast 7.

iMovie 4 and iMovie HD didn't change the input values. iDVD 4, Toast 6, iDVD 5 and Toast 7 produced identical output values.

The bottom line: there were slight changes going from DV to MPG-2 that darkened most of the patches, but the changes (although noticeable) were VERY SMALL. Moving the test clip around as digital data doesn't change much.

To see the changes, view the image at the bottom of the page.

If you see big differences between playing a clip through your camera to your TV and playing a DVD of the clip through your DVD player to your TV set, you aren't seening any digital changes. I suspect the differences are due to the digital to analog conversion process that need to happen in your camera and DVD player to display the clip on your TV - the camera and DVD player A to D processes are different.


BTW - ALL OF THE ABOVE APPLIES ONLY TO NTSC. PAL is different and I don't have the time to do THAT experiment.


The encoding methods (chroma (color) and luminance (brightness)) are different between DV and MPG-2. This affect the way the video plays back on a TV set.

http://www.scala.com/media/video-encoding.html says in part:

About converting DV to MPEG
There is some color loss due to the ways that the two formats store color data.

DV is 4.1.1 = luma/b-y color/r-y color.
MPEG is 4.2.0 = luma/color b/r alternating by fields/unused.

When DV is re-encoded as MPEG the two color channels are merged into one, reducing the quality. This may only be slightly noticeable, but should be considered. PAL DV 4.2.0 and doesn't have this problem.

 

Color bar test image from Adobe Premier 6.5

 

Patch reference numbers measured from various test images.


The DV clips were opened with Apple's Quicktime Player v 6.5.2 and still frame captures were made with Ambrosia Software's SnapzPro X v 2.0.2. Patch R, G and B values were read from the screen captured image files with Adobe's Photoshop v 7.0.1.


The DVD clips were opened with Apple's DVD Player v 4.0 and still frame captures were made with Ambrosia Software's SnapzPro X v 2.0.2. Patch R, G and B values were read from the screen captured image files with Adobe's Photoshop v 7.0.1.


Patch Still image from Premiere 6.5 DV Clip from iMovie 4 iDVD 4 Best Performance Toast 6 High Quality Video
    Original DV Clip from Premiere 6.5    
  R G B R G B R G B R G B
1 180 180 180 175 176 175 170 171 170 170 171 170
2 180 180 12 171 176 1 166 171 0 166 171 0
3 13 180 180 1 174 169 0 169 164 0 169 164
4 13 180 12 0 171 0 0 164 0 0 166 0
5 180 16 180 167 6 167 163 2 163 163 2 163
6 180 15 14 168 5 1 164 1 0 164 1 0
7 15 15 180 5 8 172 0 3 167 0 3 167
8 16 16 16 12 13 12 8 7 6 6 7 6
9 180 180 180 175 176 175 172 171 170 170 171 170
10 8 29 66 0 27 64 0 24 61 0 24 61
11 235 235 235 230 231 230 224 225 224 224 225 224
12 44 0 92 44 0 94 40 0 90 38 0 88
13 16 16 16 12 13 12 6 7 6 6 7 6
14 7 7 7 3 4 3 0 0 0 0 0 0
15 16 16 16 12 13 12 6 7 6 6 7 6
16 24 24 24 19 20 19 14 15 14 14 15 14
17 16 16 16 12 13 12 6 7 6 6 7 6
  Patch DV Clip from iMovie HD iDVD 5 Best Performance Toast 7 High Quality Video
         
    R G B R G B R G B
  1 175 176 175 170 171 170 170 171 170
  2 171 176 1 166 171 0 166 171 0
  3 1 174 169 0 169 164 0 169 164
  4 0 171 0 0 166 0 0 166 0
  5 167 6 167 163 2 163 163 2 163
  6 168 5 1 164 1 0 164 1 0
  7 5 8 172 0 3 167 0 3 167
  8 12 13 12 6 7 6 6 7 6
  9 175 176 175 170 171 170 170 171 170
  10 0 27 64 0 24 61 0 24 61
  11 230 231 230 224 225 224 224 225 224
  12 44 0 94 39 0 88 38 0 88
  13 12 13 12 8 7 8 6 7 6
  14 3 4 3 0 0 0 0 0 0
  15 12 13 12 6 7 6 6 7 6
  16 19 20 19 14 15 14 14 15 14
  17 12 13 12 6 7 6 6 7 6




  Top patch in set: iMovie HD DV Stream in Quicktime Player (DV color space)

Bottom patch in set: iMovie HD DV Stream/iDVD 5 in DVD Player (MPG-2 color space)











Click on the image to open a larger version.
     


See also Gray Patch Test at http://homepage.mac.com/prof_pixel/gray_patches/gray_patches.htm

Copyright 2005, Frederick L. Shippey, Electronic Imaging Consulting, 26 November 2005