Histogram in the Lightroom is based on the current image rendition, that is it is based on the adjustments you've made and conversion Lightroom came up with based on those adjustments as well as its internal design decisions.
Raw histogram in FastRawViewer (and RawDigger, too) is "ground truth" - it is the histogram of the raw data in the shot, before any conversions at all, "as is".
Such a raw histogram is useful when evaluating what can be extracted out of the raw data during the raw conversion; that is, for example, how much of real highlight clipping is in the file. It is also important that the raw histogram in FastRawViewer and RawDigger shows true amount of underexposure on the shot (headroom in highlights), and in FastRawViewer it is easy to see how much exposure can be added.
Raw histograms allow to diagnose false channel clipping, like when shooting saturated objects (flowers, for example). It is quite an often complaint that when shooting a red rose under daylight the red channel clipping indication based on the "conventional" histogram (in-camera or in a raw converter; Lightroom being one of raw converters) is premature, thus leaving the detailed blue channel underexposed and noisy. For the similar reason, photographers complain on the noise in the red channel in the sky. This happens mainly because before displaying the warning in the conventional case white balance is applied, multiplying the raw values in red and blue channels by 1.6 to 3. Having raw histogram allows to avoid such false warnings and to select (for raw conversion) among the series of exposure-bracketed shots the one that is correctly exposed.
The amount of clipping to be allowed is somewhat of a personal choice, generally I consider 0.3% in the strongest channel OK, if not in a single important area (to see what is clipped press "o" to display clipping overlay). Normally 0.3% poses no problem at all for Lightroom highlight recovery feature (even if in a contigious area of the shot).
Underexposure limit is user-selectable. Depending on the camera and ISO setting as well as on my intended image use I may set it between 7 EV and 10EV. The default is reasonable 8 EV. The reason to keep the underexposure limit below 8 EV is not just noise, but also flare and glare considerations. Flare and glare result in the loss of linearity in shadows, which makes white balance and colour control problematic. At -8 EV typical flare in a well-controlled studio shot causes non-linearity of more that 2/3 EV.
I hope I addressed some of your questions. Please feel free to ask futher. Your questions help us understand what needs to be covered in workflow mini-manuals and tips.
Dear David,
Dear David,
Histogram in the Lightroom is based on the current image rendition, that is it is based on the adjustments you've made and conversion Lightroom came up with based on those adjustments as well as its internal design decisions.
Raw histogram in FastRawViewer (and RawDigger, too) is "ground truth" - it is the histogram of the raw data in the shot, before any conversions at all, "as is".
Such a raw histogram is useful when evaluating what can be extracted out of the raw data during the raw conversion; that is, for example, how much of real highlight clipping is in the file. It is also important that the raw histogram in FastRawViewer and RawDigger shows true amount of underexposure on the shot (headroom in highlights), and in FastRawViewer it is easy to see how much exposure can be added.
Raw histograms allow to diagnose false channel clipping, like when shooting saturated objects (flowers, for example). It is quite an often complaint that when shooting a red rose under daylight the red channel clipping indication based on the "conventional" histogram (in-camera or in a raw converter; Lightroom being one of raw converters) is premature, thus leaving the detailed blue channel underexposed and noisy. For the similar reason, photographers complain on the noise in the red channel in the sky. This happens mainly because before displaying the warning in the conventional case white balance is applied, multiplying the raw values in red and blue channels by 1.6 to 3. Having raw histogram allows to avoid such false warnings and to select (for raw conversion) among the series of exposure-bracketed shots the one that is correctly exposed.
The amount of clipping to be allowed is somewhat of a personal choice, generally I consider 0.3% in the strongest channel OK, if not in a single important area (to see what is clipped press "o" to display clipping overlay). Normally 0.3% poses no problem at all for Lightroom highlight recovery feature (even if in a contigious area of the shot).
Underexposure limit is user-selectable. Depending on the camera and ISO setting as well as on my intended image use I may set it between 7 EV and 10EV. The default is reasonable 8 EV. The reason to keep the underexposure limit below 8 EV is not just noise, but also flare and glare considerations. Flare and glare result in the loss of linearity in shadows, which makes white balance and colour control problematic. At -8 EV typical flare in a well-controlled studio shot causes non-linearity of more that 2/3 EV.
I hope I addressed some of your questions. Please feel free to ask futher. Your questions help us understand what needs to be covered in workflow mini-manuals and tips.