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Prevent blown-out, white-hot spots in your photos – A75

August 08 2012 - Photo Technical

Welcome aboard photo enthusiasts.  I’m always reading various articles on photography, and recently I was reading about the incredible 12.5 stop dynamic range in 16-bit RAW format of the Phase One IQ180. This is amazing! The very best dynamic range from a professional 35mm digital SLR is around 6 stops in 12-bit RAW.  What would it be for a point and shoot? In any case, you understand my excitement.  Well, possibly you don’t.

The previous two articles dealt with the absolute importance of having the correct exposure in taking any and all photographs through properly using your camera meter and the histogram. The objective of those articles was to explore a question posed to me I wonder (next month) if you might address hot spots in photos. I noticed that our little point and shoots do this a lot, especially with yachts. Since so much of the picture is white (hulls, crew uniform shirts, etc) that we struggle with keeping an appealing tone throughout. If we have to use a fill flash like we did over the weekend with the cloudy skies and rain, then it’s even worse. This is all on the auto setting. How can we control this in a manual setting? We continue to explore the problem and what we can do about it starting with looking at dynamic range.

What does dynamic range mean? It’s all the tones between and including pure black and white. At a single pupil dilation the human eye can discern about 17 stops, and if allowed to adjust it is capable to appreciate 30 stops.  Each stops is twice or double the illumination of the previous level. In layman’s speak this means the eye has the incredible capacity to see things in great detail in the darkest shadows to the brightest highlights.

Now that we are aware that the top 35mm SLR’s are capable of 6 stops in 12-bit RAW you can easily realize the camera is far less capable compared to the human eye in its ability to see. Talking about hot spots our point and shoot cameras will take the many levels our eyes (17 at a single pupil dilation) and compress them to at best 6 levels, and this can result, for instance in bright white settings, clipping or burned out highlights.

Let’s review this high key (having lots of white and brightness) photo below….

At the bottom of the photo within the red box is the histogram representing the photo (note- this is only an approximate illustration I made to further this discussion). The part marked A represent darker areas in the photo – the hair, shaded areas, the sky. Part B is for the face and C for white areas not clipped. All the places marked D are hot spots or areas  that are clipped as indicated by the straight (black) line on the far right edge of the histogram. Clipping on the right is for all white areas that have lost detail that is not recoverable, with exceptions not applicable except possibly with the most expensive equipment, that is not with pocket cameras.

It will be hard to see, but looking closely at the pupil there is a small circular spectral highlight. This tells me a flash was used, as it should be to fill in the dark shadows around the eyes. The shadows are still too deep giving a raccoon eye look, but knowing the limited capability of the pocket flash this was likely unavoidable. It does tell me that in this photo the flash had no part in creating hot spots, which can be best spotted from reflective surfaces, including perspiration.  All the hot spots were the result of strong sunlight that the limited dynamic range of the camera could not handle.

At the start of this column you might have noticed that attached to the number of stops was added “16 bit RAW.” I have written about RAW (but only to 12bit), JPG (8 bit), TIFF files.  Let me simply tell you at this writing that 16 bit RAW is the most powerful combination of information of a photo that has been taken. Using the camera’s proprietary raw conversion software allows for some stretching of the dynamic range.

Say what? Are you having an information overload?  This is the bottom line…this is the third column on this topic. The first covering meter reading and 2nd covering the histogram reading are essential in maximizing the dynamic range of the photo you take, which will help minimize problems with hot spots. If you want to reduce those even more, better expensive equipment will help.  You can pick up that Phase One IQ180 for $43,000.00.  While you’re shopping I’ll take permission to go ashore.