Sun, May 15th 2011, 9:44PM:


... that I've been posting pictures almost regularly until beginning of March and then, whoops, a two months break! I've taken quite some pictures since then: I've shot almost every meal/dinner I've prepared in the past weeks; I'm getting better at it, but I'm not yet convinced to put any of these pictures on my blog!

I've also spent some thoughts and done some experiments regarding shooting "dramatic looking" skies and clouds. I guess people usually do this by adding a red or an orange filter to their lens. I didn't get myself to buying one of these filters, since I'm not fully sure they won't impact and fool my 30D's exposure measurements. Instead I've decided to work on a shooting technique getting you a nice "red channel" that might (or might not) look quite similar to the results achieved by a true red filter and a proper exposure.

For many years I've been using the channel mixer for getting a monochrome image mainly containing the initial image's red channel. I used that monochrome image as a new "value channel" for the initial image, resulting in a nicely darkened sky while keeping clouds very bright. While doing so I always noticed that, unfortunately, the sky became rather noisy. It took me some time to realise that this is because daylight has a rather cold colour temperature, i.e. there's not much red light in there. During the RAW converter's white balancing, the red channel is, thus, most often multiplied by 2 or more (UfRAW users can directly see the "red multiplier" in the white balance tab), boosting the contained noise.

That's where my 30D's playback histogram get's annoying: The histogram shows the image _after_ white balance has been applied, i.e. after the red channel as been scaled. This definitely is funny, since in playback mode an image's red channel might seem fully blown out, while (when looking at the RAW file's histogram) it still might be underexposed 1 stop or more.

So, how to get a properly exposed (raw) red channel for nice b/w images? Using UfRAW I've simply entered a "red multiplier" of 1, so no scaling would be applied to that channel. According to the software, a "red multiplier" of 1 corresponds to a colour temperature of something around 3200K. That's the value I've now set my 30D's manual colour temperature ("K" mode) to... et voila! The playback preview looks awfull (greenish and bluish), but when loading the image in UfRAW, the (raw) red channel histogram almost exactly matches the red channel histogram shown by my 30D!

Probably I'm the only guy crazy enough to play around with such settings... but I just thought of dropping this down here: Maybe somebody might just find this useful!


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