Noise and Colors

[buywisdom]

I am relatively new to photography. I upgraded from a Panasonic P&S to a Rebel Xti this summer. I have been reading about the color spaces and pixel sizes and I have a few unanswered questions:
1)Assuming that larger pixels equals less noise does this mean if I take the same pic wit the same settings at 10mp and 8mp on my Xti I will have less noise on the 8mp? Is this equivalent to reducing the quality later? Is this a stupid question, am I missing something?
2)The color gamut for Adobe RGB is larger than that of sRGB but they have the same 8bit per channel plus on alpha channel. Thus ~16M colors limitation is the same for both spaces? Right? Are there ways of capturing more colors and/or light variations without this bracketing HDR business. It this a color space or camera or both limitation. Are their alternatives or ways of capturing say 12bit or 16 bit per channel. I don't mean going to 16bit per channel when editing I mean capturing it. I realize that a conventional monitor is limited to 16M colors so I am not sure how you could view it all without some loss.
3)I was wondering about the optical limitation of the human eyes. How many colors can we see? How many alpha channels? Maybe this quesiton is beyond the scope of this forum but if you have any idea I would love to know.

 

[Grimace]

1. Nope, it is the fixed size of the pixels compared to the fixed size of the sensor. 10MP on a point and shoot (very small sensor) will be much more sensitive (ie. noise) than an XTi - and likewise a 10MP full frame (slightly bigger sensor) camera will have even better noise performance.

 

[zdobson]

You can get 16bit photos by shooting in RAW and converting them to either tiff of psd files. However, monitors are only 8bit, so you won't really be able to see a difference on your monitor. Also, unless you're making really large prints, you probably won't see the difference there, either. Tiffs are about 5 times the size of jpgs, so I wouldn't save too many photos that way. If you really are concerned about the quality of the photos, always shoot RAW.

As for noise, the thing that makes the biggest difference is shooting at the lowest ISO possible, regardless of what megapixels the camera has. I've heard that Photoshop plug-ins like Noise Ninja can do a good job, but I haven't tried it personally. Most noise reduction methods other than shooting at low ISO has the risk of making the entire photo less sharp.

 

[robbieduncan]

2) Shoot in RAW: it doesn't use 8bpc (bits per channel). It uses 16. Although not really: the XTi actually only uses 12. Newer Canon bodies like the 40D use 14. Of course the software on your computer then turns this into 8bpc images for display but you have more data to choose from allowing highlight/shadow recovery.

3) We (and cameras) don't see alpha channels: they are only there in images for compositing. We see the final output of a composited real world scene.