From: "maltetewes" <maltetewes@yahoo.fr>

Date: May 2, 2009 4:12:55 AM MDT

To: Astro_IIDC@yahoogroups.com

Subject: fire-i : saturation of red channel

Hi all,

I'm using an inexpensive unibrain fire-i colour camera (640x480 8bit) with the latest Astro IIDC 4.04.00, and have troubles with the dynamic range / saturation. First off all, let me say that I don't believe that these issues are related to this or that recent update of Astro IIDC, as I would have noticed this and I observe them for some time now.

As it's probably more a general question, I thought let's post this here.

The easiest-to-describe symptom is that using the "Red Channel Monochrome" mode, I can't get the saturation to happen on the right ("white") edge of the histogram. Saturation occurs somewhere at two thirds (181/255) of the dynamic range, independently of my adjustments of Brightness, Black Point, and Exposure.

Is there any extra setting/preference that I am missing ? It does not depend on the "Enable CCD Over Drive register optimization" checkbox.

Using the Green or Blue Channel Monochrome mode, the behaviour is different : a low position of the "Brightness" slider makes the image saturate below 255 if exposition time is too high, but all I have to do is to move this brightness slider towards higher values and the saturation peak in the histogramm can be brought "beyond" 255. If I then reduce the exposure time to avoid saturation, I get more or less the full dynamic range on the screen, as it should.

If I switch to "Monochrome" mode, same problem : red still saturates at the same value (producing a sharp peak in the histogramm), whatever the setting of Brightness, Black Point, or Exposure time is. I just can't get 255-pixels on the sreen, even if I completely overexpose all I get is a grey at 231.

But in "Color" mode, the "Red Gain" slider alows me to perfectly adjust the saturation level, so that it occurs beyond 255. I can get well exposed images with full dynamic range, and a maximum value of 253 in the video preview. So I'm guessing my camera is ok.

Is there perhaps any way to tweak these gain sliders, or the way the colors are mixed, in the monochome-like modes, or does someone has similar experiences ?

Cheers,

Malte