Douglas Burns wrote:> > Have been following this thread for a while, and staring to get a bit > confused. With all due respect to David Kay I just don't follow his logic. I > agree with all the other posts that the dynamic range is simply the > difference between the highest and lowest values recordable (hence the term > "range"). This is something I was taught on my first day of college (and the > reason I'm writing this post in simplistic terms with the minimum of > jargon!). The bit rate simply determines the number of discrete steps within > that range that the device can record.
Am I deep in the hot cocky cack or what? At the risk of being banished to the colonies forever... Can we agree that Dynamic Range is the ratio between the lightest and darkest Tonal Values which can be detected and/or reproduced? Any argument here? And can we agree that Bit Depth is the number of Tonal Values in which a Contrast Range is divided? I certainly hope so! Then this leaves the issue of how a CCD responds to light reflected from the subject. Electrons are generated proportionate to the intensity of light. So when twice as many electrons are generated, up to the saturation point of the CCD, we have one f-stop more exposure. And when half as many are generated, we have one f-stop less exposure. Agreed? I'm not counting electrons here, here's an arithmetic example... In an earlier post, I suggested that a two-stop under-exposure with an 8-bit device would provide a range as follows: 64, 32, 16, 8, 4, 2, 1. Now with a 16-bit device, here's what we get with a two-stop under-exposure. 16384, 8192, 4096, 2048, 1024, 512, 256, 128, 64, 32, 16, 8, 4, 2, 1 Now on the basis that light generates electrons proportionately, then it's clear to me that the 16-bit device is a clear winner with 8 f-stops more being resolved! I know the CCD is an analogue device and it's here where voltages are created to represent the various light levels. However, in a capture device, the A/D converter is also of primary importance. It must be be capable of converting every voltage at each pixel from analogue to digital data. I have heard that a manufacturer can save a lot of money by fitting a lower specified A/D converter. I believe I can see the effect of this as less "sparkle" in an image! And you can actually see this when images are compared side by side that are taken under identical conditions! Most images seen in isolation look reasonable until you compare two devices this way. Some photographers don't pay more for this level of quality. And finally, there's the frequency at which the data is read out from the CCD. Faster shooting speeds implies that the read-out of data is over-clocked and therefore of lesser quality than provided by the optimum or slower frequency. The result is more noise. Phew. I rest my case your Honour. Am I to be banished down-under forever? Best regards, David Kay =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
