Exposure
Purpose: Use to approximate adjustment of image tone in terms of exposure.
Please note that this doesn't actually adjust the exposure, that can only be done when the image is
exposed in the camera. Two ways to apply this tool:
- compensation: The slider adjustment is
expressed in EV, where each whole number is a stop. The tool's range is -5/+5 stops. The reset
button returns the setting to 0.0.
- target patch:This method allows one to designate a patch of the image and scale the
rest of the image with that patch as a 'gray' reference. The selection is done on the main
image pane by moving the mouse cursor to the image location to be used, holding down the Shift key,
and clicking the left mouse button. A cross will appear on the image pane to mark the location,
and the location's xy coordinates will be displayed in the tool pane. Patch selection must be
accomplished prior to selecting this mode. The gray level used to perform the operation is
specified in the ev0 box as a number between 0.0 and 1.0; 0.18 is the default, which corresponds to
the predominant notion of 'middle gray' as 18%. The patch size is
specified as a radius from the center of the center pixel; the default is 1.5, which designates a
3x3 patch.
Note that the specification of the gray level is tied to the image data range. The 0.18 default
is for the internal floating point image's data range of 0.0 to 1.0. 14-bit raw
data, with a range of 0 to 16383 maps to 0.0 - 0.25 in floating point, so for 14-bit raw files
you either need to change ev0 to 0.045 (0.25 x 0.18), or scale the image with the blackwhitepoint tool using the data mode prior to applying patch exposure compensation.

Properties: See tool.exposure.* in Configuration Properties