I saw this on the Yahoo 10D group and thought others with Canon DSLR's might find the concept interesting. Has anyone here actually tried compositing two images for this purpose?
Tom P. > QUOTE : > > Digital Darkroom Questions e-mail list > August 11, 2003 > > Enjoy today's questions... > > Tim Grey > Editor, The Digital Image > [EMAIL PROTECTED] > www.timgrey.com > > ########## > > You raised a point on DDQ 8/8/03 that many of us haven't fully grappled with. You say a digital camera sensor has a much wider range of sensitivity to tonal values than film but the exposure latitude is about the same as slide film. Does that mean a single RAW capture can be brought in with one conversion for shadow detail and another for highlight detail and the two "exposures" composited, whereas if only one conversion is done you are stuck with compressing the tonal values into a narrower range? Or does it simply refer to the fact that you can "amplify" the same sensor to higher ISOs, with some noise penalty, of course, but cannot capture the full range of sensitivity in a single exposure -- even a RAW one? > > ========== > > The basic answer is that an imaging sensor in a digital camera doesn't have an inherent limit to the range of tonal values it can capture. The sensor is simply converting photons into an electrical charge, with the strength of the charge representing the tonal value captured. While each photodiode on the imaging sensor can only hold so much charge, the range of possible values is quite high. The biggest limit on the effective tonal range of the image is the file format being used. For example, if you capture in JPEG mode, the image will be 8-bit per channel, which means there are only 256 possible tonal values for each of the three channels. Most digital cameras that offer high-bit capture are actually converting the analog signal to data values using 12-bit values. This provides a total of 4096 tonal values per channel, which provides for significantly more smooth gradations of tone and color. > > Because a RAW capture records the actual values recorded by the sensor, and does so in high-bit, there is much more information (detail) retained in the image. This allows the image to adjusted significantly while still holding good detail. An image that has been exposed reasonably well can generally be darkened by up to one stop and lightened by up to two stops in the RAW conversion process while retaining detail within the image. > > So, yes, you can create composite exposures from RAW captures. In the RAW conversion, simply keep one of the images slightly dark, for example to optimize the sky, and the other image bright, for example to optimize the foreground. The two exposures taken from the same capture can then be blended in Photoshop to produce a final image with detail that could not normally be obtained with a single exposure. > > > > UNQUOTE * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
