Center-Weighted Option for Auto and Manual Tone Settings
The Auto Settings control was updated in Lightroom 7.1 to process cropped images using only the cropped pixels image data. This provides more accurate calculation of the Basic panel Tone control settings by excluding the image data not visible in the cropped image.
A problem was encountered recently by a user who was processing panorama image sets shot with a Canon 8-15mm F4L fisheye lens. To minimize the number of images required he set the lens to 12mm focal length, which reveals the lens image circle as fully black corners.
When syncing develop setting from one image to the others in the panorama set he noticed the nadir (straight-down shot) image files always looked darker than the surround image files. They are much lower in dynamic range (i.e. pavement or grass) and the image adaptive nature of the Tone controls produces different rendering. This is due to the black corners in the image, which have the same pixels values in every image file even though the scene referred lighting is different.
In trying to find a solution the ‘Idea’ presented here to provide Auto and Manual Tone Settings center-weighted adjustment was borne.
It is also useful with the current Auto Settings and Manual Tone controls to provide better rendering similar to a camera’s center-weighted exposure metering.
1) Provide an option in the Basic Tone panel to manually select a crop area used by both the Auto Settings and manual Tone controls. This crop area should be applied separately from the Crop Overlay tool so the tone rendering remains the same when syncing settings across cropped and uncropped images.
2) The Auto and Manual Tone control settings should be “image adaptively” calculated and applied using only the image data inside the crop area.
3) Provide an indicator inside the Basic panel to alert the user when a center-weighted crop area is selected.
4) (OPTIONAL, but desirable) Provide an elliptical selection tool to allow both circular and elliptical selection of the area used when calculating image adaptive Tone settings. This provides more flexibility in accurately excluding black frame areas in partial and full-circular fisheye lens images and with lenses that have high vignetting.