Camera Recomendation Please!!!

[Matt the Teckie]

Hi Mike,

SystemQ's quite right, it's your classic Dynamic Range issue.

There are mainly two types of wide dynamic range camera, the first using conventional CCD sensors and the other using a CMOS sensor.

The problem you have is that the voltage charges on all pixels in a CCD array are read and cleared around 50 time a second (or whatever shutter speed the camera's set to). This means if some pixels are under exposed you'll get a dark region and if over exposed you'll get blooming. CMOS chips, although they don't have nearly the same low light performance opererate in a different way.

Each indervidual pixel has it own memory built into the chip. Therefore, if the camera decides that the developed voltage level isn't high enough yet, it doesn't update the DSP. The end result is that the pixels are feeding information into the camera at different rates depending on the amount of light falling on them.

Wide dynamic ranges are supported by CCD driven cameras but they usually have to take two shots of the same scene to produce a single frame (or pair of fields), one with a fast exposure time and one with a slow exposure time. Unfortuanly this process takes time. In this mode, the camera usually either resends the previous fields while it thinks about the next pair (presents as tracing during motion rendering) or it sends a blank sync pulse during this period (presents at a noticable flicker)

There are four ways you can cure this. First, add more lighting therefore decreasing the dynamic range of the scene. Second, decide which scene is more inportant (bright area or dark area) and set the back-light compentation to be sensitive to the area you want to cover. Third, use a wide dynamic camera (Samsung are ok but Ikegami are excellent if you have the reddies), these are both dual shot CCD cameras though. Fourth, use an ultra wide dynamic range CMOS camera (Baxall HyperD).

Hope this helps