On Thu, Feb 26, 2009 at 06:58:28PM -0500, Fernando wrote: # On Thu, Feb 26, 2009 at 5:31 PM, Bob W <[email protected]> wrote:
# I haven't really bother trying it (so far so good with whatever I get # with autoWB), I was really trying to understand what did Adam mean # with "However its only truly useful for the RAW shooter as a good # histogram delivers the best data, not necessarily the best looking # JPEG." For your raw file to hold the most data, you want the brightest areas to be just below full scale (for 12 bits full scale would be 0x0FFF in hex) and your darkest values would be just over 0. eg. the darkest shadow would be at 0x003 and the brightest highlight at 0xFF9. And, if the raw data didn't have 12 bits of range, it would be better for the data to range from 0x0803 to 0x0FF0 (the top half of the range) than from 0x0003 to 0x07F0. If you have two bits of noise in your raw signal, when you process it to the final image, the file that ranges from 0x0803 to 0x0FF0 the noise gets reduced along with the signal, rather than in the file that ranges from 0x0003 to 0x07F0 where the noise would get amplified with the rest of the signal. The exposure that gives you the best raw data, would therefore look overexposed if converted directly to a JPEG. Or, at least, that's the theory of "Expose To The Right". There are a couple of things to be careful of though. One is that the histogram is based on a very compressed and averaged image, so if the highlights are small enough, they may be averaged out with neighboring pixels, and not show up as blown pixels in the histogram. The other is that if you only have a single histogram, and you're shooting a subject with a very saturated color, you could clip that channel, while the histogram would only show the level averaged over all three channels. -- Photographs are like sentences, the best ones have both subjects and verbs. Larry Colen [email protected] http://www.red4est.com/lrc -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
