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Luminance Report Densitometer

MegaVision's workflow is based on knowing how bright the scene is, how the important reflectances within that scene relate to each other, and how they fit on the target. A three dimensional scene wants to be perceived as three dimensional on the two dimensional rendering surface, be it transmissive or reflective. In order to best achieve the intended rendering, adequate local contrast must be present, in addition to a total contrast that fits the target.

Most workflows are concerned with effecting the total contrast of the file onto the target after capture, using Adobe® Workflow products such as Shadow and Highlight, Levels (input and output), and the HDR file format. Local contrast is often improved with selections on which edits are performed through masks, using blending modes and calculations on individual or master channels. This method can result in images that suffer in rendering if the edits are a little overdone, especially when various selections are handled differently. The final appearance can be artificial - more illustrative than photographic.

MegaVision's method emulates Ansel Adams' evaluation of scene contrast, exposure and development, to manufacture an appropriate number of useable tones for the intended target rendering. Photoshop® is used to fine-tune the image for final use, but the edits tend to be subtle-- tonal adjustments designed to lead the eye across or through the image, or chrominance adjusts designed to fabricate color adjacencies desired by the shooter.

The question becomes how a photographer can make the exposure and subsequent development fit the target. Image sorting in a post processing state can work if the scene contrast fits perfectly in the target's density range. But there's a relationship between the tonality of the target paper and the tonality of the scene, which can be rendered correctly by the tonality of the "digital emulsion" used to capture the scene.

Key to the evaluation of the scene is a report called luminance. Luminance may be defined as: A measure of the brightness or luminous intensity of light. Most digital camera meter reports do not display luminance, preferring instead to involve a histogram that reports ratios of RGB. Ratios of RGB levels are typically not used to evaluate brightness but to imply color, which changes according to the RGB working space. RGB levels are used to evaluate brightness, but only at highlight and shadow, where the endpoints are essentially neutral and the levels report can be understood. What about important reflectances between highlight and shadow? What evaluates RGB levels to see if an object is too light or too dark? Levels are not used for that task; the recommendation to make a light evaluation is to use a calibrated monitor.

With the exception of MegaVision, camera back devices have an RGB levels densitometer that reports only ratios of RGB.

For example: How bright is 122R-48G-213B? Indoors, the brightness may be relative to the condition of the monitor display and the viewing environment, but the data the printer receives isn't what is seen on the monitor. The display on the monitor is the data modified by a display profile, a white point, a display gamma, and possibly an output profile. Outdoors, in a variable viewing environment, brightness level is even more difficult without a calibrated display.

The display of luminance would simplify the dilemma. Photographers have traditionally used a luminance value when utilizing a light meter's report quite effectively.

Light meters don't have display gammas, monitor profiles, or require specialized viewing environments-- they work equally well outdoors or in a studio, which is exactly why a well designed tool is valuable. MegaVision enhances the light meter by allowing pixel accurate measurements of luminance; color coding luminance according to the paper's rendering characteristics.

What Adams used so successfully was a luminance report. As an example, his recommendation for an image that includes a Caucasian skin tone in open shade, was a zone VI and a half. With a MegaVision luminance report, the photographer can view 6.5 if provided with the exposure. It is also possible to view a luminance report in zones (0-10), in ink density (0-100%), or in gray levels of 0-255. When MegaVision displays light metering, the photographer views both luminance and each amount of R, G, and B.

Luminance is calculated by adding the contribution of red, green, and blue to the photometric measure of the brightness-- where red contributes 28%, green contributes 60%, and blue contributes 12% to luminance. The RGB levels reported by Camera RAW, Lightroom®, and Capture One will display the ratio of these colors but the brightness is communicated only by the data modified by the display gamma, white point, and monitor profile-- which may be unavailable when out in the field. The zero to 10 luminance scale that Ansel developed is a practical and useable report when evaluating scene contrast and placing the exposure of important reflectances.

MegaVision's Photoshoot software reports luminance in levels, percentages, and in zones. This flexibility within the software makes possible the best crafting of the photographic vision.

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