Our goal should be to avoid clipping in the highlights while maintaining acceptable noise levels. The principal tool for judging exposure levels is the histogram, which shows the precise luminance levels of the red, green, and blue pixels after setting the ISO and white balance. Monitors, while indispensible, are less than ideal for gauging brightness.
The histogram allows us to see how brightness is distributed throughout the image and how near the shadows and highlights are to clipping. However, the histogram alone is incapable of indicating correct exposure: it can’t warn us of areas in the image that are about to, or that have already clipped, which is where the false color tools and traffic lights come in.
The RED Komodo has two false color modes: false color exposure and false color video. The false color exposure mode alerts us to clipping in the highlights (indicated in red) and clipping in the shadows (purple) in addition to indicating 18% gray (green). There is often a great deal of exposure latitude here before an excessive amount of purple or red occurs. The false color video mode furnishes us with more granular information regarding brightness levels in different areas of the image but should be used at ISO 800 and above for the most accurate results. Its colors are based on IRE values, not the RAW data and is useful for evaluating lighting and for adjusting a suggested look prior to sending footage off to post-production. There are nine levels, with green representing 18% gray, pink corresponding with typical Caucasian skintones, teal signifying textured shadows and straw, yellow and orange approaching ever closer to white, while the remaining colors indicate the tonal extremities.
The red, green and blue dots, commonly referred to as the traffic lights, inform us of when a particular color channel is clipping. When around 2% of the pixels for an individual color channel have become clipped, the corresponding traffic light will be triggered. Sitting between the highlight and shadow traffic lights are the goal posts. The fullest extent of each goal post represents a quarter of all the image pixels for a particular color channel. Ordinarily, the shadow goal posts can be raised by as much as 50% and still yield acceptable noise levels: but even a miniscule amount in the highlight goal posts can spell disaster, especially in HDR.
Which is why we shouldn’t make a fetish of exposing to the right (ETTR) – the practice of recording as much light as possible without clipping, causing the histogram to be bunched up to the right – to begin with, because the histogram does not represent the raw pixel data, the risk of losing important highlight information forever is real, particularly at lower ISOs. Furthermore, rapidly changing subject matter and lighting conditions increase the odds of clipping highlights. A more prudent approach is to record only as much light as necessary, not as much as possible, while still maintaining noise at an acceptable level. Slight underexposure is no sweat, while highlight clipping means detail is lost forever (it must be acknowledged though, that clipping of reflections and specular highlights is sometimes unavoidable). We’ll reserve the discussion of ISO for another day!