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Dear Sir:

The most common practice with cameras, in our experience, is to render the midpoint (the raw data number resulting from exposing according to a simple metering, like spot or centre-average) as 117 (assuming they use sRGB and Adobe with simple gamma 2.2, here is the supporting calculation: 0.18^(1/2.2)*255 = 116.9).

FastRawViewer determines dynamic range down from clipping point, clipping point being determined either by the explicit number in the file metadata ("camera provided highlight limit" in FastRawViewer Preferences -> "Image display" -> Exposure tab, this may be a bit conservative), or by recognizing the histogram shapes characterisical to clipping - please have a look at

The EV0 point is based on our knowledge of calibration of in-camera meters, for each individual camera model. The standard suggests close to 3 EV headroom (the "distance" between the midpoint and clipping). Thus the generic calibration for rais about 12.7%, not 18% as many beleive. Camera designers often deviate from this generic recomendation ensuring even more headroom to protect the highlights (thus the myth of cameramakers "overstating ISO speed"). The less "noisy" is the system, the more headroom in highlights could be afforded; except mostly for "extended" ISO: for extended loISO the calibration is offset to leave less room in highlights compared to regular ISO speed settings, for extended high ISO the opposite may take place; there are other exceptions, too. Adobe are referring to this calibration game while explaing the need for Baseline Exposure. Please have a look at and pp. 93, 88, 139 of FastRawViewer Manual.

You can see the value of Baseline Exposure in the "BLE" field in EXIF panel of FastRawViewer.

For your convenience, FastRawViewer Manual comes with the installation (main Menu - Help - "PDF Manual") and is fully searchable. You can also download it separately in higher resolution from - direct link is