Look at the factors and compromises in digital photography workflow to avoid or minimize blown out highlights.
There is no single factor delivering a major reduction in blown out highlights in the the digital workflow of high quality digital photos. As with all consistently good digital workflow it is matter of a number of compromise decisions, depending on the specific circumstances, and the photographer’s artistic intent of how they want to portray the scene.
What are Blown Out Highlights
These occur when the tonal range of the scene from darkest black to the brightest white exceeds the photographic system’s ability to reproduce that range of tones. This can results in a loss of detail in the delicate lighter shades, instead they are displayed as solid white,
File Format
Always shoot in RAW format because the image data is commonly saved in 12 bit format giving 4,096 brightness levels, or 14 bit then there are potentially 16,384 different brightness levels. This gives much more information for later stages of the digital workflow and sophisticated RAW processors such as Adobe Camera Raw, Bibble Pro or DXO Optics, can extract seemingly lost highlight information.
If the image is saved as a jpeg in a digital camera then the potential number of of brightness levels drops dramatically to only 256 in an 8 bit image format. This loss of image information is sufficient for the final output of the digital workflow but severely limits the hope of recovering blown out highlights in digital photos.
Camera Choice
Dynamic range is not where near the top of the digital camera marketer’s list of features used to sell their wares, but it is important to advanced photographers.
The DxOMark dynamic range lab test results in the graphic at the bottom of the page compares a compact digital camera (P7000), an entry level DSLR (D3000) and an advanced DSLR (D7000), all the cameras are from Nikon. The more advanced the camera the greater the dynamic range, measured in Exposure Value stops the camera can handle.
ISO
The DxMark test also reveals that the dynamic range varies with the photographer’s choice of ISO, or light sensitivity, setting on the camera. for all the cameras in the comparison their maximum dynamic range is at their minimum ISO setting. So try to keep the ISO as low as possible to help minimize blown out highlights.
Expose to the Right
This an exposure adjusting technique where photgrapher’ take test shots and adjust the exposure settings using the camera’s histogram as a guide. The camera’s LCD histogram shows the number of pixels with pure white as the right end end of the histogram. The practice is to adjust the exposure to minimize the number of pixels recording pure white.
The screen shot at the bottom of the article shows the histogram for a digital photo with blown out highlights. The light colored trim of the old grandstand reflected too much light for the camera to capture properly and still expose the main part of the scene correctly. The small peak in the graph at the extreme right hand side shows there are likely to be blown pixels in the digital photo.
Consider the Noise
The downside of the Expose to The Right technique is that deliberately underexposing the image makes digital noise in the darker areas more of a problem. This means photographers should use restraint and not overly rely on this technique.
HDR and Tone Mapping
Finally there is the emerging technique of High Dynamic Range imaging and the associated process of Tone Mapping. The full HDR process is not always practical, especially with a moving subject, or the photographer is not using a tripod. It is possible to extend the dynamic range of an image and rescue single shot images with blown highlights. This is more successful if the original image is saved in RAW format. Photomatix is a popular HDR application with a tone mapping facility and the latest DxO Optics Pro RAW processor also incorporates a single shot HDR function.
The blown out highlights in the picture of the old grandstand were rescued using single shot HDR digital workflow in Bibble and Photomatix.
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