Can we really avoid noise in our digital photos? Yup this what had popped in my mind just now. Was browsing all photos of Miss Malaysia Universe 2008 and as expected some photos comes with an ugly noise. While this is so disturbing i google the net to see if we can really avoid noise in our photos. So below is what i found.
If you want to avoid noise the first thing to do is use a camera equipped with a sensor having a high native sensitivity (typically, a DSLR with a large sensor and large photo sites), and use a low ISO setting. This keeps amplification at a minimum.
You can also use noise reduction, if your camera supports it. With this feature the camera first makes the intended exposure, followed by another exposure of the same length, but with the shutter closed. The second image contains only the noise that occurs at the current temperature with the current sensor. The data of the second image is then subtracted from the first image, resulting in an image with strongly reduced noise (noise is not zero; because of the random nature of noise, the second image is not 100% identical with the noise of the first image). This noise reduction technique is called “dark frame subtraction”, and many cameras offer it for longer exposures.
You can also use software to suppress noise that still ends up in the image. But suppressing noise instead of avoiding it in the first place, and at the same time not losing image detail is a tricky task. You need sophisticated software and know how to use it well.
Other than this, there is not much the photographer can do.
For sensor makers, there are a few things more that can be done. Thermal noise can be avoided by cooling down the sensor. However, this is not practicable for photo cameras, but only for sensors attached to telescopes etc. But camera makers can at least avoid heating up the sensor too much.
Sensor makers can also increase native sensitivity, on one hand by making photo sites large, and on the other hand by increasing quantum efficiency, i.e. increasing the fraction of photons actually causing a charge increase. But quantum efficiency is already high, around 70%. So even if quantum efficiency is increased to 100% (which is unlikely), sensitivity can at most increase by 1/3. And photo sites tend to shrink instead of grow, because of the never-ending demand for higher pixel numbers.
Sensor makers can also improve their signal processing chain, making sure that noise introduced there is as small as possible. Moving towards CMOS sensors instead of CCD sensors is one way, because with CMOS sensors the processing electronics is closer to the individual photo sites.
My internet connection totally down. my Phone has no dial tone. when i call my house number, to my surprise the lady told me ” Nombor yang anda dail tiada dalam perkhidmatan” .
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…Nah…nah nah…goood goood evening and welcome back! For the past 2 months, I received lots of Emails and Sms asking me if i do photos editing service.
