Blue skies turn gray.

Question

I wonder if anyone can check this behavior in CS3.
I noticed that simply applying the Magic Bullet Looks effect, without ever opening the Looks Builder and making any adjustments, that my blue skies turn gray. Viewing on a calibrated, external NTSC monitor, the original DV footage shows a very clear delineation between blue sky and white clouds. After adding the effect, I get a sort of gray mush, with no delineation between clouds and sky. My once beautiful day looks overcast and about to rain.
Upon further investigation, I found some more possibly useful data.
For starters, all MB effects cause this to happen - Looks, Colorista, Frames, Deartifactor, Misfire, etc. I then checked several other effects native to Premiere Pro 2.0, such as Levels, and found them to be causing the same issue when applied, even before any changes had been made with the effect. Not all effects do this, however. The Fast Color Corrector, for example, does not change the video in any way until I make a change to the effect parameters. Same with the other effects in the Color Correction folder.
I then tried other clips with sky in them, some from the current project, some from other projects (meaning they were shot on a different day, on a different tape, so camera issues could potentially be eliminated). Some of the other sky clips exhibited the same issue, others did not.
Eventually I took a look at my clips through Premiere's built-in scopes. I found that the clips showing a problem had IRE levels in the sky portion of the image ranging from a low of 80 to a high of 120. Applying the effects in question immediately compressed that range, making the lows about 90 and the highs about 100.
I haven't the technical knowledge to even guess at a cause, let alone a solution, so if anyone has any thoughts, please share. I'd really like to keep my blue skies!

Answer 1

I guess this starts to get to the heart of the matter.
>"Digital video is created using an 8-bit (or sometimes 10-bit) quantization of the incoming analog image. With 8-bit digital video, the 7.5 to 100 IRE analog range is divided into 256 steps between total black (0) and total white (255). In RGB values, 0 to 255 is the full range, but according to the 601 specifications, the range for YCrCb digital video was reduced so that black = 16 and white = 235. This was done to accommodate "real world" video signals that tend to exceed both ends of the scale and to accommodate the set-up level of NTSC.
>Unfortunately, not all NLEs work this way. Some take video in and digitize it based on the 0-255 range, while others use the 16-235 range. Since no video can exist below digital zero, any analog video, which is lower than 7.5 IRE or higher than 100 IRE, will be clipped in a system that scales according to the 0-255 range, since there is no headroom on such an NLE. Some NLEs that work in this RGB mode will correct for the headroom issue as part of the conversion done with the incoming and outgoing video signals."
Seems like Premiere is keeping the DV as YUV until the effect is applied, where it goes to RGB. Bummer. My skies really looked a nice shade of blue.