Different shades of red
November 28, 2007 § 6 Comments
When filming surgery, some special issues must be considered. One of those are the color red.
Because of the blood running through our body, most of our organs and tissue is some shade of red. To distinguish the different anatomical structures from each other it is crucial that the video system used is able to reproduce the colors accurately.
DV and HDV
DV, and recently also HDV, are very popular formats both in the medical world and in the video production community. Both DV and HDV are heavily compressed formats. They run at approx. 25 Mbit/s. Some of the reduced data rate is obtained by lowering the chroma sample rate. For both DV (PAL) and HDV the sampling format is 4:2:0 (more on chroma subsambling here). The recorded color signal is under a quarter less accurate than the luminance signal. This is simply not enough to reproduce the different shades of red satisfactory.
This is the main reason why I shoot on DVCPro50 when I can. Not only is this format less compressed (50 Mbit/s), it also uses a sampling format of 4:2:2. The recorded chroma signal is 50 % as accurate as the luma signal. This results in little to no visual difference from 4:4:4 sampling, as our eyes are more sensitive to luminance than to color.
Using DVCPro50 largely increases the ability to reproduce the colors of our insides accurately. When shooting minor surgery and biopsies I use the Panasonic AG-HVX200 in DVCPro50 mode with the Firestore FS-100 hard disc recorder and the DVRig Pro camera support.
For shooting major surgery I have just built a custom made camera support. Footage from this system is currently recorded on DV.
More about the handheld rig and my new surgery video system later.