DV Digital-Analog Transfer Curve

 
I measured the digital->analog transfer function for the Sony DCR-TRV900 and TR7000 cameras. I generated an 11 step grey bar chart in Photoshop with pixel intensities running from 0% to 100% grey scale. 100% means RGB pixel values of 255,255,255. The actual image I used is shown here (click to enlarge). I transferred this image to the cameras via firewire.

I don't have a waveform monitor, so I used a Tektronics TDS210 digital oscilloscope (60 MHz bandwidth, 1 GHz sample rate). I used a 75 ohm load at the input, with an actual measured value of 74.82 ohms. Below are the waveforms taken from the TRV900 and TR7000 cameras while playing back the image above (click to enlarge). The captured data from the oscilloscope was transferred digitally to a computer, and captions added

 

The two cameras have matching output waveforms, to within the noise level of the output circuit + oscilloscope sampling noise. Note that black (intensity =0%) pixels are below IRE 0 (not legal NTSC) and white (intensity = 100%) pixels are above IRE 100 (also not legal).
When recording live from its own lens, the TRV900 does not record any pixel values below 10% white regardless how dark the scene is, but it does go up to 99% white pixels in light areas, suggesting that analog video out can exceed IRE 100. The measured correspondence between pixel intensity and analog output level in IRE units is shown in the table below.
 
 

Pixel, % White
IRE Level
0
-7.5
10
4.0
20
16
30
28
40
39
50
52
60
63
70
75
80
86
90
98.5
100
109

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