Just like the pixel-buckets, there can be no fractional values on the ADC: any levels that are partially filled will be rounded down to the closest ADC level. As an example, an 8-bit ADC has fewer levels, so the overlay might look something like this: To see the effects of this second type of gradation, let’s overlay the ADC levels on top of our electron well-depth levels from the previous post on our pixel. The ADC bit-depth for many common DSLRs can be found at, or from the manufacturer's specifications for dedicated astrophotography cameras. This is usually 8, 10, 12, 14, or 16 bits, and the number of levels or possible values that can be read off by the ADC is 2 raised to the number of bits (256, 1024, 4096, 16384, and 65536 levels respectively). The ADC has its own levels that corresponds to the bit-depth of the ADC. While the bucket itself is graduated in the electrons it can hold, there is another step of gradation that occurs when the pixel is read off by the ADC. This emptying also readies our pixel buckets to gather photons for the next image. These gathered electrons create a voltage difference, and it is this voltage that is measured to give us the brightness or intensity value on each pixel. The collected photons are converted to electrons as mentioned earlier. The captured light and the corresponding electrons are an analog signal, and this needs to be changed to a digital signal so that we can work our pre- and post-processing magic on our images. This process is carried out by your camera’s on-board Analog to Digital Converter (or ADC). I’ve now mentioned many times about the pixels being “read out," or recorded, or measured. So come on down once again to the realm of the tiny buckets! The ADU and You Adequately covering this topic can be technical like part 3, but I've got plenty of diagrams to help out as well. It is now time to investigate the way we measure what we've captured and how it gets turned into an image that we can actually work with. Up until this point all of our captured rain/photons have been kept nicely inside our buckets. You can find part 1 here, part 2 here, and part 3 here. If you are unfamiliar with things such as well-depth and others, I recommend taking a quick look back at the previous installments. Per usual, what will be covered below builds upon and applies to concepts already covered. Welcome back to this blog series! We've already covered tons of fascinating topics in the previous sections.
0 Comments
Leave a Reply. |