color correction- raw vs. filter vs. manual white balance

[HowardE]

Raw is as close to shooting film (with digital) as you can get. What you shoot is what is written. [WIKI]Camera_raw[/WIKI]

Aperture and Shutter speeds are actual apertures and shutters, and not a process.

Underwater (and topside), a filter will decrease the available ambient light. As stated before, slower shutter speeds can compensate for this without sacrificing depth of field with lower (larger) aperture settings. Topside, when I shoot landscapes, I typically shoot at F32 or there about, with a circular polarizer filter. I often (even in bright daylight) have to shoot at .5 - 1 second shutter speed for proper exposure - therefore I use a tripod. - Underwater, there are issues with setting up a tripod, and taking a landscape portrait this way.

When you use a digital camera, the shutter opens (just like a film camera) as wide as the aperture setting, and the image hits a CMOS sensor instead of a piece of film. The RAW image is written... If the camera writes a JPEG, it first interprets the color space, and compresses and writes the file.

 

[Charlie99]

Gee, my notion is still that a filter can be used in some cases to increase the signal to noise ratio of whatever the weakest color is ,

That's a valid notion, but generally the advantage of reducing red noise is less than that of keeping faster shutter / smaller aperture.

You can have quite a bit of noise in the red but still have a pretty good looking picture. Our eyes are more sensitive to noise in the overall luminosity or in the green channel. That's why most sensors have twice as many green sensors as the other color.

Probably before red noise becomes a problem, "banding" effects will be a problem. That's what happens when, because you have very few steps in red, when you increase the gain, you get visible steps in color rather than an apparently continuous change. Most likely to be seen in a big section of nominally blue water that changes color a bit as the angle to the sun changes.

I've gotten some pretty bad banding in photos looking upward at the sun through blue water. The area away from the sun is underexposed, making the low levels on red even lower. That's a case where a filter would help. I haven't tried it, but I suspect that in bad cases of banding like that, then adding some noise back into the red channel (after doing levels/gain adjust) would actually improve the photo by elminating the banding.

 

[stillhope]

I was just trying to add some perspective to answer the question: "If your camera has RAW, you are wasting money and light with a filter... Since you can adjust the red channel (and colour temperature) later in software, why would you reduce the light even further?"

My point was that by using a filter (and opening the aperture or slowing shutter) you can actually increase the amount of red if that is what you need to improve your s/n. Up here in the Pacific Northwest, I use a filter because my histograms show a huge green signal, a small blue one, and a very tiny red one -- the normally low red levels underwater are exacerbated by the phytoplankton acting as a green filter. If I boost the blue, super-boost the red and reduce the green in post processing the result is not nearly as good as if I used a filter.

I'm not saying that a filter is right for every occasion, but there are times when I find it to be the right tool for the job.

 

[CLA]

Thanks for all the advice Howarde, John, Alcina, Charlie, Jim. I think I'll play around with RAW first and try a filter if I continue to get bad pics. Jim, reduced copies of the pics I posted are in my photo gallery and the EXIF data is indicated there. If you need the originals I can email them to you. Thanks again