Tag: Ralph Nordstrom

HDR Exposure

This is the third in a series of articles on high dynamic range, more commonly known as HDR.  The previous article illustrated how HDR situations occur; namely, when the dynamic range of the subject exceeds the dynamic range the sensor (or film) is capable of capturing.

But with digital photography there is a technique for dealing with it.  In the field, it begins with taking multiple shots at different exposures so that the combined dynamic range exceeds that of the subject.

Continue reading “High Dynamic Range #3 (HDR)”

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In the first posting we discussed how colors are translated into three numbers in a digital camera, one for each of the three primary colors – Red, Green and Blue (RBG for short).  After all, digital cameras are computers complete with processors, memory and software.  We described the 8 bit color mode in which the numbers range from 0 to 255 and are used to measure and store the brightness of each color.  Zero is darkest dark possible and 255 is the brightest bright possible.  When all three colors are combined in equal proportions you end up with gray.  If all three colors are zeros (0,0,0) you have pure black; if they are all 255s (255,255,255) you have pure white.

Camera Sensor Dynamic Range

The next step in this journey of understanding it to realize how the pixels in the camera sensor work.  Recall that each pixel is really three pixels – one for each of the primary colors.  While the following is an oversimplification, suffice it to say that the sensor has a built in dynamic range that can be measured in stops.  That is to say, the range from the darkest darks to the brightest brights that the sensor is capable of capturing can be measured in stops.  This is also true of all films.  For example, the dynamic range may be as little as five stops (generally most color positive films) and as much as ten stops or more (generally the most advanced digital cameras). For the remainder of this discussion we can assume our camera has a dynamic range of 7 stops.  It can be illustrated in this way….

 

Continue reading “High Dynamic Range #2 (HDR)”

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This is the first in a series of articles that address the fascinating topic of High Dynamic Range or HDR.  HDR not only refers to situations you face when photographing in the field but also the digital darkroom techniques for processing HDR images.  This first article will lay the groundwork necessary for understanding HDR.

How often do you look at your photographs and are dissatisfied because the images appear washed out, or at least parts of then.  Maybe you took an outdoor family shot at a gathering or picnic.  The people may look great but the sky is washed out.  Or perhaps you were on vacation and something similar happened – part of the image was washed out.  The opposite could also happen.  The image could be too dark.

Normally modern digital cameras have very sophisticated built in light meters that give you excellent exposures.  But often the conditions of the scene you are shooting are simply beyond the capability of camera to capture, regardless of whether you’re shooting digital or film.

If you’re collecting pictures for the family album these defects may not be a problem at all.  It’s the memories that the photograph conjure that are important, not the technical merit of the image.  These are photographic records of important events in our lives.

But if you’re intention is to create a work of art, a washed out image is one sure way to frustrate your efforts.  If you’re shooting RAW you have some ability to recover washed out highlights or black shadows.  However, once you’ve completely lost your highlights and/or shadows there’s nothing you can do to recover them.

Continue reading “High Dynamic Range #1 (HDR)”

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