Hi Bob, Film, like the human eye, is very sensitive to subtle differences in tones at the darker end of the scale. It is very insensitive to the differences at the brighter end. Digital, on the other hand is linear, equally sensitive to all light levels. However, when shooting RAW you have only 12 bits per channel to describe all tones. The first bit has only the values 0 and 1 to describe the darkest tones. The sixth bit has the values 32 thru 63 to describe the middle tones. The 12th bit has the values 2048 thru 4095 to describe the brightest tones. Fully 1/2 of the data is in the last, highest, "stop". Where film is very good at recording dark tones, digital is very poor. That's why with digital you try to keep the exposure as close to the high end of the histogram as possible without actually blowing out the highlights. This keeps the shadows as high as possible in the range, up where there are as many values as possible to describe them. Down at the low end there is more noise than tonal information. RAW converters are also very adept at recovering highlight data as long as least 1 color channel has some info for it to work with. Sometimes as much as 2 stops worth, not so the low end, too noisey.
Don > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of > Bob Sullivan > Sent: Tuesday, July 04, 2006 10:23 AM > To: Pentax-Discuss Mail List > Subject: Re: exposure evaluation ... digital and film > > > Godfrey, > You've got to explain this. > Digital sensors can't give any detail in overexposed highlights. > You can recover details in underexposed areas with post processing. > So don't you want to avoid blown highlights at all costs? > Regards, Bob S. > > On 7/4/06, Godfrey DiGiorgi <[EMAIL PROTECTED]> wrote: > > Sensors respond to light differently compared to film. Chapters one > > and two of Bruce Fraser's "Real World Camera Raw with Photoshop CS2" > > explains why there is a difference. As a result, exposure evaluation > > requires a different mindset and different settings. JPEG and slide > > film, although they are different, generally end up taking about the > > same exposure. > > > > However, underexposing in RAW by 0.3-0.5 EV is exactly the wrong way > > to go. In general, with the *ist DS, I find my average exposure for > > RAW capture requires +0.3-0.7 EV additional exposure compared to JPEG > > or slide film. > > > > Godfrey > > > > > > On Jul 4, 2006, at 7:09 AM, Jens Bladt wrote: > > > > > I didn't know there was a different mindset for digital - except > > > for trying > > > harder to avoid overexposure/blown out highlights. I usually regard > > > JPEGs as > > > slides, RAW as negs. > > > I have BTW noticed that I'm not the only one who normally underexposes > > > deliberately by 0.3-0.5 F-stop. (I shoot RAW 99% of the time). > > > > > > -- > > PDML Pentax-Discuss Mail List > > [email protected] > > http://pdml.net/mailman/listinfo/pdml_pdml.net > > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
