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Photography & Print Production Notes
ISO = International Organization for Standardization
In photography it refers to Film speed (or the digital equivalent).
In the "old days" it was referred to as ASA (American Standards Association).
It refers to the light sensitivity of the film and is indicated by the number. The lower number meaning it is less sensitive thus requiring more light to register the image.
A ISO 200 rating is twice as sensitive as an ISO 100 rating etc.
The basic way to make use of it is when you are shooting in lower light you would increase the ISO rating.
This then gives you the opportunity to use a faster shutter speed (or smaller aperture).
Examples would be sports photographers who need to get shots of action in failing light, they would upgrade the ISO so they can shoot at faster shutter speeds.
Or, shooting concerts where flash is not allowed or wanted.
The trade of is that at higher settings the grain would be more visible (in digital it means more "noise").
Iso is used to rate how sensitive film, or in your case, the sensor is to light. Iso works hand in hand with aperture and shutter speed to determine the perfect exposure for a given scene.
Typical iso ranges for digital slrs are 100-3200. Some may go to as low as 50, while others as high as 12800. The higher the iso number, the more sensitive the sensor is to light, thus allowing a faster shutter speed and/or smaller aperture without introducing motion blur into the picture. Say for example, the exposure is ISO 200 @ 1/200 of a second and f/5.6, if you decide to set the iso to 400, the light sensitivity is effectively doubled, thus allowing a 1/400th of a second exposure at f/5.6
The trade off is, the more sensitive the sensor (higher iso settings), the "noisier" your picture gets. Noise in a image, in layman's term, is more commonly described as "grainy". The higher the iso, the "grainer" your shots would be, and thus the loss of detail. With digital point and shoots, iso 400 is the maximum you can get to without pictures without getting grainy; while with dslrs, ISO 1600 (and beyond) is generally still very usable. This is one of the reasons why you bought a dslr; for the excellent high iso performance.
ISO is a measurement of the sensitivity to light of a light sensitive surface, whether film or digital sensor. It is also one leg of the "Exposure Triangle". The other legs are f-stop (aperture) and shutter speed. All three must work in harmony to produce a correct exposure.
A low ISO - 50, 100 - is very insensitive and requires a lot of light. We use it on a sunny day and when we want the best image quality. In film its said to have small, almost invisible, grain; in digital its said to have very little, if any, noise.
A high ISO - 200, 400, 800, 1600 - is more sensitive and requires less light. We use it on an overcast day (200) or for sports/action (400), or for low-light, non-flash photography (800, 1600). In film a higher ISO is said to have more grain; in digital its said to have more noise.
If our goal is to make large prints from our negatives or digital files we will use a low ISO, with our camera on a tripod. If we're using digital then we'd also use our camera's highest resolution.
The "speed of the aperture" is not an accurate term. A lens' aperture is simply the opening of the iris. It's primary characteristic is how wide the opening is. There is no speed associated with it. Although on any particular shot, there will be a certain "speed" (shutterspeed) related to how wide the aperture is, it is a term more directly related to the *shutter* than the aperture or ISO.
ISO, in the photographic sense, is a standard measure of light sensitivity for your imaging medium. There are actually TWO standards to speak of (and before ISO became *the* standard, there were *other* standards, like ASA...but let's not get sidetracked). Folks will always refer to "film speed," which is a reference to the ISO standard for light sensitivity in *film* imaging, which technically not the right definition to refer to anymore. Actually these days, most people refer to *digital imaging* ISO, which is similar, but different than film ISO. The term itself--ISO--It's really a shortened reference to the International Organization for Standardization's, which documents many standards, not just film speed and digital still camera exposure index standards.
ISO earned the name "film speed" because a film emulsion that is more sensitive to light would require less exposure time to capture an image (or alternatively, a smaller aperture). A film that took less time to expose a shot was considered a "faster" film, hence, a higher ISO rating. Faster films were useful to shorten the exposure time necessary to catch low-light shots. But a downside to those film stock was that the grain of the emulsion was rather noticable in development--literally, bigger fatter crystals vs. slower film emulsions. You would get grainy pictures. If you ever shot an old b&W 3200ISO film, you would remember how grainy the images were compared to the same image shot with an ISO100 film.
The digital photography equivalent ISO standard is actually an entirely separate set of ISO standards. But it serves the same purpose--a method for assigning and identifying ISO standard speed ratings, ISO standard output sensitivity values, and recommended exposure index values, for digital still cameras. The ISO rating says that a given photosensor array, must be able to produce a particular image quality for a manufacturer to be able to say that it takes images at that ISO rating (technically called a "digital still camera exposure index").
Unlike film, which is capable of working at only one ISO rating, photosensors are capable of operating at various ISO sensitivity ratings because their output signal can be electronically amplified. Is your sensor actually "becoming more sensitive to light?" No. You can't change a sensor's native sensitivity. You're simply turning up it's output signal. So, when you set a digital camera to take pictures at an ISO1600 setting instead of ISO100, you're telling it to amp up the weaker signal so that it will still produce an image of a particular light intensity given a specific amount of incoming light.
But here's the key for you...just like film speed ISO, photosensor ISO loses image quality when you force the photosensors to work at at higher sensitivities and with less light. The root cause isn't emulsion grain (as it is in film ISO's problems), but signal noise. Since you have less light to work with, the camera tries to "turn up the volume" to reach higher ISO sensativities, as if you were trying to hear a very quiet song over your radio. The "image signal" becomes more and more difficult to distinguish from the "static," or noise. You'll see mottled variations in the color of a blue sky, for example, when in real life, the sky is a smooth blue color. That's image noise, and it's significantly more noticable in higher ISO settings.
So, when taking pics, when should you put it in high ISO? The answer is debatable. But if photodocumenting what you see is your objective, the answer is as seldom as you possibly can. Keep the ISO as low as possible to avoid unnecessary noise. This, of course, is only an issue when you're trying for low-light shots without flash. You'll find that in brightly lit scenes, or when using a flash, you can always stick to ISO100 or ISO80 (some cameras go as low as ISO 50). But when the lights dim, and you have an artistic preference for not using flash, that's when you'll have to start pushing the ISO up. What happens is that the shutter speeds start to get so long that you can't keep the subject from blurring in the picture. That's when you know that you're going to have to push the ISO up. If your subject is inanimate (doesn't move), then you can avoid pushing ISO up by putting your camera on a tripod, and use those longer shutterspeeds to get more light in the camera. But if your subject is moving, then you'll have no alternative but 1) push ISO up, or 2) use a flash. If you use a flash, you'll change the artistic impression of the shot. If you push the ISO up, you'll concede image quality. Both are a mixed bag. One thing you could do if you had the option, is switch to a camera/lens that is capable of wider aperture settings, letting in more light. Lenses that can stop down to f2.0 or less are highly sought after for it's ability to catch images in low light without going up to a noisy ISO.
There is one camera company (currently) that is changing the relationship between noise and higher ISO. To get to the higher ISO indexes, instead of just turning up the volume on a regular sensor, Fuji has put the work into developing a more sensitive sensor. Somebody smart is working at that company. They've been blowing away competition with their Super CCD sensor, by getting lower noise in high ISO shots without the need of noise-reduction algorithms (which can reduce noise only by sacrificing image detail), and as far as sensor technology goes, theirs is the best sensor out there to date. Personally, I hope to see other manufacturers follow its lead.
One last note regarding noise, and photography with high-ISO. It can be argued that *some* noise is not only an acceptable part of imaging, but can lend character that can add to an image's artistic qualities rather than detract. Would old world-war II era photographs posess quite as much nostalgia if they didn't have that grainy texture? That sepia tone? That point is of course debatable ad nauseum, when imaging steps away from photodocumentation, and into photography as an art form.
Source(s):
Here's a thorough discussion on film speed, with references to older standards as well.
In traditional (film) photography ISO (or ASA) was the indication of how sensitive a film was to light. It was measured in numbers (you’ve probably seen them on films – 100, 200, 400, 800 etc). The lower the number the lower the sensitivity of the film and the finer the grain in the shots you’re taking.
In Digital Photography ISO measures the sensitivity of the image sensor. The same principles apply as in film photography – the lower the number the less sensitive your camera is to light and the finer the grain. Higher ISO settings are generally used in darker situations to get faster shutter speeds (for example an indoor sports event when you want to freeze the action in lower light) – however the cost is noisier shots. I’ll illustrate this below with two elargements of shots that I just took – the one on the left is taken at 100 ISO and the one of the right at 3200 ISO (click to enlarge to see the full effect).
(you can see larger sized images of both shots here for the 100 ISO and here for the 3200 ISO)
Read more: http://digital-photography-school.co...#ixzz2GRKhTZVl
Digital "noise" is a common problem in digital cameras today. A lot of factors can introduce noise to your digital photography,[1] but there are certain steps you can take to avoid it, as noise can obscure detail and removing it from your images can take precious time.
Digital noise usually represents itself as speckled pixels of colour in your images or as a grainy effect, and is generally considered undesirable. Read on to find out how to reduce the chances that your valuable images will be affected by digital noise.
EditSteps
1. 1
Understand what a digital camera sensor is, and how it works. Unlike analog cameras, digital cameras work with a sensor instead of film. Sensors receive light and process it into electric charges via tiny photodiodes, whose outputs are reflected as pixels in your final digital image.[2] These electrical charges tell the sensor what colour each corresponding pixel is meant to be and other information which will create the digital image.
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2. 2
Understand what digital "noise" is and what causes it. When light hits the sensor's photodiodes, a signal of electrons are produced in order to convey the light to the camera sensor. Electronic "noise" is the unwanted fluctuations in this signal.[3] In a digital camera, noise manifests itself as speckles, usually colored and patternless. These are generally caused by unwanted electron flow in and around the sensor adding to the desired electron flow. Noise can be caused by imperfections in the sensor itself such as "hot pixels"[4], randomness in the distribution of the limited numbers of photons available at low light levels,[5] and the sensor or camera overheating[6].
3. 3
Purchase higher-end, newer camera equipment. The most convenient, but expensive, way to combat noise is to buy a newer camera if yours is a few years old, with more expensive cameras being able to deliver better performance. Newer cameras have sensors that are developed to collect more light with less noise than those in older cameras, making them a good choice if you are struggling to control noise in your images and your gear is outdated.
o Choose a camera with a larger sensor. The problem with smaller sensors is that the light sensors are closer together than in a larger sensor, and that means the electrons overheating corrupt them faster due to their closer proximity. A larger sensor means that electrons will have to travel farther before corrupting their neighbouring light sensors. Full frame sensors are perfect for reducing noise in your images. A DSLR or large-sensor compact camera such as one in "Four Thirds" format is much better than a compact camera, even one a few years newer, although a full-frame DSLR is better still, as fast wide-angle and prime lenses for it are more widely available and cheaper.
o Pick a camera with fewer megapixels, or a lower resolution, in a given class. The more pixels there are on a camera's sensor, the closer they are together and the more likely overheating electrons will corrupt the light sensors. Although higher-end cameras generally have larger sensors with a high resolution or megapixel count, there are those which have larger sensors but still retain lower megapixel counts, making them perfect for dealing with digital noise.
o Pick a wide-aperture lens to maximize light intake. Some compact cameras have f/2.0 or f/2.8 lenses; a 50mm f/1.8 lens is inexpensive and excellent for a DSLR.[7] These will allow the same shutter speed at one-half to one-quarter the ISO setting of a common f/3.5 or f/4.5 maximum aperture zoom lens (At the same f/ratio, the bigger camera is still better: it's collecting equally intense light into bigger photosites, for far more photons to process. The absolute size of the aperture for a given angle of view matters more). Lenses are a much more mature technology than cameras, so an interchangeable wide-aperture lens will improve your photography through many camera upgrades. Image stabilization allows faster shutter speeds but tends not to be built into wide aperture lenses, making those better overall as they stop subject motion too; a fast lens and compatible in-body image stabilization is a great combination.
4. 4
Switch your camera's exposure to manual mode and adjust the settings which may introduce noise. When the camera is on automatic, or in program mode, as is the case with most lower-end cameras of the "point-and-click variety", your images are more likely to have noise as the camera changes the exposure by itself, and quite often it will introduce factors that introduce noise to your images. Taking control of your camera and exposure settings will help you eliminate factors which could contribute to digital noise in your photographs. Your camera's instruction manual will contain all instructions on how to adjust the various settings on your camera.
o It's OK to use a semi-automated exposure mode, but be sure to manually set a low ISO if possible. For instance, you could use aperture-priority mode with a wide aperture, which will allow a relatively short shutter speed with any given ISO. You could use your camera's exposure-compensation or bracketing function to try different exposures near the one the camera thinks is right.
o Reduce your ISO. ISO is the setting which controls how light sensitive your camera's sensor is. A lower ISO (for example ISO 200) means your sensor is less sensitive to light, but is also less likely to create digital noise, while a higher ISO (for example ISO 400, or ISO 800) makes your camera sensor more sensitive to available light, but also increases the chance your images will have noise. Check your camera's manual on how to adjust the ISO setting.
If you need a higher ISO for a correct exposure with a fast-enough shutter speed to avoid blur from a lack of camera support or moving subject, use it. Adding a few speckles of high-ISO noise is better than smearing the picture with blur or wiping out its shadow detail with underexposure.
o Use a faster shutter speed, or rather, avoid long exposures. Long shutter speeds (for example, exposures of 5 seconds, or 30 seconds or longer) create more noise as they make the camera's sensor overheat faster. Faster shutter speeds give less chance for the sensor to overheat. So consider adding more light to your image to reduce the exposure time, and reduce the chance of noise: turn on some lamps, or use a flash. If you can't add more light, or it would spoil the picture (like one of lights outdoors at night), a slightly slower shutter speed and a lower ISO will provide the best results, as described below.
o Increase your signal-to-noise ratio with a low ISO and generous exposure.[8] If you let a lot of light into your camera, preferably quickly, it will overpower the noise and give you an acceptable image. Use a low ISO setting, which amplifies the sensor's signals relatively little, and exposure to go with it (Some kinds of noise can accumulate over time, and even accrue more rapidly as the sensor warms through use, but a longer exposure is still generally better than a higher ISO). The lowest setting is usually best, but you'll usually have to look for noise to notice it up to ISO 400 with a compact camera or old DSLR, and up to ISO 1600 with a modern (2011) DSLR.
5. 5
Turn the camera's noise reduction setting on, if it has one. This feature is usually found in higher-end cameras. In-camera noise reduction is usually helpful in combating noise in your images, especially those of a longer exposure or in low light conditions. However be aware, it does smooth the fine detail in your images, making them softer to the eye, which can be problematic, so only use this setting if you feel that noise will a serious problem while shooting. PC software can often smooth noise in post production, while preserving detail better than that supplied in the camera's internal computer, and you can revert to your original image if you decide you didn't want so much smoothing, or even any at all.
o You can use "dark frame subtraction" – making a preliminary or subsequent "exposure" of the same length as the actual exposure but with the lens capped to detect noise to delete from the final image to compensate for "hot pixel" and other camera imperfection noise.[9] Some cameras can do it automatically, not bothering to open the shutter for the dark exposure, but you can perform it yourself, even with a compact camera.[10] This technique does not smooth your image, so is a suitable option for those who are worried about other noise reduction methods.
6. 6
Make your image as bright as possible. It may seem obvious, but the less shadow there is in your image, the less chance noise will have together there. Noise generally appears in darker areas of your images (where there's less light to overpower it), so whether you introduce a new light source, such as a lamp or flash, move to a better-lit area, change your exposure settings to allow more light or photograph lighter subjects, reducing the amount of shadow in your image will reduce the amount of noise.
o Night pictures can be tricky because the highlights are actually the light sources. Like the sun during the day, they're much brighter than the surrounding areas which receive and reflect back to the camera only a little of their light. A camera's light meter averaging their brightness with their surroundings as if they were ordinary highlights will underexpose them for one big, noisy over-dark shadow. Try increasing the exposure significantly over what it suggests.
o Very bright lights can cause streaking or "bloom" with the CCD sensors usually found in cheaper cameras. Try to avoid having them close-by in the image.
7. 7
Avoid using digital zoom, such as those frequently found on lower-end cameras or "point-and-click" varieties. Digital zoom is technically not zooming at all; it is in fact cropping and enlarging from a small area of the sensor. It should especially be avoided when that small area is clouded by noise.
8. 8
Keep your camera stored in a cool place before you use it. The cause of most noise is a thermal reaction. The warmer your camera is, the more likely the sensor will overheat in a shorter period of time. Making sure your camera is cool, especially when in hot conditions, can greatly improve your camera's performance and reduce the likelihood of digital noise. Excessive heat such as that in uninsulated areas of a car in the sun, will be harmful for cameras regardless.
9. 9
Take further steps to combat noise in post production, such as the aforementioned "dark frame subtraction" or noise reduction software. Sometimes, no matter what actions you take to reduce noise, it may still occur in your photos. In these cases you should take the time to learn and implement noise reduction in post processing.
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In photography it refers to Film speed (or the digital equivalent).
In the "old days" it was referred to as ASA (American Standards Association).
It refers to the light sensitivity of the film and is indicated by the number. The lower number meaning it is less sensitive thus requiring more light to register the image.
A ISO 200 rating is twice as sensitive as an ISO 100 rating etc.
The basic way to make use of it is when you are shooting in lower light you would increase the ISO rating.
This then gives you the opportunity to use a faster shutter speed (or smaller aperture).
Examples would be sports photographers who need to get shots of action in failing light, they would upgrade the ISO so they can shoot at faster shutter speeds.
Or, shooting concerts where flash is not allowed or wanted.
The trade of is that at higher settings the grain would be more visible (in digital it means more "noise").
Iso is used to rate how sensitive film, or in your case, the sensor is to light. Iso works hand in hand with aperture and shutter speed to determine the perfect exposure for a given scene.
Typical iso ranges for digital slrs are 100-3200. Some may go to as low as 50, while others as high as 12800. The higher the iso number, the more sensitive the sensor is to light, thus allowing a faster shutter speed and/or smaller aperture without introducing motion blur into the picture. Say for example, the exposure is ISO 200 @ 1/200 of a second and f/5.6, if you decide to set the iso to 400, the light sensitivity is effectively doubled, thus allowing a 1/400th of a second exposure at f/5.6
The trade off is, the more sensitive the sensor (higher iso settings), the "noisier" your picture gets. Noise in a image, in layman's term, is more commonly described as "grainy". The higher the iso, the "grainer" your shots would be, and thus the loss of detail. With digital point and shoots, iso 400 is the maximum you can get to without pictures without getting grainy; while with dslrs, ISO 1600 (and beyond) is generally still very usable. This is one of the reasons why you bought a dslr; for the excellent high iso performance.
ISO is a measurement of the sensitivity to light of a light sensitive surface, whether film or digital sensor. It is also one leg of the "Exposure Triangle". The other legs are f-stop (aperture) and shutter speed. All three must work in harmony to produce a correct exposure.
A low ISO - 50, 100 - is very insensitive and requires a lot of light. We use it on a sunny day and when we want the best image quality. In film its said to have small, almost invisible, grain; in digital its said to have very little, if any, noise.
A high ISO - 200, 400, 800, 1600 - is more sensitive and requires less light. We use it on an overcast day (200) or for sports/action (400), or for low-light, non-flash photography (800, 1600). In film a higher ISO is said to have more grain; in digital its said to have more noise.
If our goal is to make large prints from our negatives or digital files we will use a low ISO, with our camera on a tripod. If we're using digital then we'd also use our camera's highest resolution.
The "speed of the aperture" is not an accurate term. A lens' aperture is simply the opening of the iris. It's primary characteristic is how wide the opening is. There is no speed associated with it. Although on any particular shot, there will be a certain "speed" (shutterspeed) related to how wide the aperture is, it is a term more directly related to the *shutter* than the aperture or ISO.
ISO, in the photographic sense, is a standard measure of light sensitivity for your imaging medium. There are actually TWO standards to speak of (and before ISO became *the* standard, there were *other* standards, like ASA...but let's not get sidetracked). Folks will always refer to "film speed," which is a reference to the ISO standard for light sensitivity in *film* imaging, which technically not the right definition to refer to anymore. Actually these days, most people refer to *digital imaging* ISO, which is similar, but different than film ISO. The term itself--ISO--It's really a shortened reference to the International Organization for Standardization's, which documents many standards, not just film speed and digital still camera exposure index standards.
ISO earned the name "film speed" because a film emulsion that is more sensitive to light would require less exposure time to capture an image (or alternatively, a smaller aperture). A film that took less time to expose a shot was considered a "faster" film, hence, a higher ISO rating. Faster films were useful to shorten the exposure time necessary to catch low-light shots. But a downside to those film stock was that the grain of the emulsion was rather noticable in development--literally, bigger fatter crystals vs. slower film emulsions. You would get grainy pictures. If you ever shot an old b&W 3200ISO film, you would remember how grainy the images were compared to the same image shot with an ISO100 film.
The digital photography equivalent ISO standard is actually an entirely separate set of ISO standards. But it serves the same purpose--a method for assigning and identifying ISO standard speed ratings, ISO standard output sensitivity values, and recommended exposure index values, for digital still cameras. The ISO rating says that a given photosensor array, must be able to produce a particular image quality for a manufacturer to be able to say that it takes images at that ISO rating (technically called a "digital still camera exposure index").
Unlike film, which is capable of working at only one ISO rating, photosensors are capable of operating at various ISO sensitivity ratings because their output signal can be electronically amplified. Is your sensor actually "becoming more sensitive to light?" No. You can't change a sensor's native sensitivity. You're simply turning up it's output signal. So, when you set a digital camera to take pictures at an ISO1600 setting instead of ISO100, you're telling it to amp up the weaker signal so that it will still produce an image of a particular light intensity given a specific amount of incoming light.
But here's the key for you...just like film speed ISO, photosensor ISO loses image quality when you force the photosensors to work at at higher sensitivities and with less light. The root cause isn't emulsion grain (as it is in film ISO's problems), but signal noise. Since you have less light to work with, the camera tries to "turn up the volume" to reach higher ISO sensativities, as if you were trying to hear a very quiet song over your radio. The "image signal" becomes more and more difficult to distinguish from the "static," or noise. You'll see mottled variations in the color of a blue sky, for example, when in real life, the sky is a smooth blue color. That's image noise, and it's significantly more noticable in higher ISO settings.
So, when taking pics, when should you put it in high ISO? The answer is debatable. But if photodocumenting what you see is your objective, the answer is as seldom as you possibly can. Keep the ISO as low as possible to avoid unnecessary noise. This, of course, is only an issue when you're trying for low-light shots without flash. You'll find that in brightly lit scenes, or when using a flash, you can always stick to ISO100 or ISO80 (some cameras go as low as ISO 50). But when the lights dim, and you have an artistic preference for not using flash, that's when you'll have to start pushing the ISO up. What happens is that the shutter speeds start to get so long that you can't keep the subject from blurring in the picture. That's when you know that you're going to have to push the ISO up. If your subject is inanimate (doesn't move), then you can avoid pushing ISO up by putting your camera on a tripod, and use those longer shutterspeeds to get more light in the camera. But if your subject is moving, then you'll have no alternative but 1) push ISO up, or 2) use a flash. If you use a flash, you'll change the artistic impression of the shot. If you push the ISO up, you'll concede image quality. Both are a mixed bag. One thing you could do if you had the option, is switch to a camera/lens that is capable of wider aperture settings, letting in more light. Lenses that can stop down to f2.0 or less are highly sought after for it's ability to catch images in low light without going up to a noisy ISO.
There is one camera company (currently) that is changing the relationship between noise and higher ISO. To get to the higher ISO indexes, instead of just turning up the volume on a regular sensor, Fuji has put the work into developing a more sensitive sensor. Somebody smart is working at that company. They've been blowing away competition with their Super CCD sensor, by getting lower noise in high ISO shots without the need of noise-reduction algorithms (which can reduce noise only by sacrificing image detail), and as far as sensor technology goes, theirs is the best sensor out there to date. Personally, I hope to see other manufacturers follow its lead.
One last note regarding noise, and photography with high-ISO. It can be argued that *some* noise is not only an acceptable part of imaging, but can lend character that can add to an image's artistic qualities rather than detract. Would old world-war II era photographs posess quite as much nostalgia if they didn't have that grainy texture? That sepia tone? That point is of course debatable ad nauseum, when imaging steps away from photodocumentation, and into photography as an art form.
Source(s):
Here's a thorough discussion on film speed, with references to older standards as well.
In traditional (film) photography ISO (or ASA) was the indication of how sensitive a film was to light. It was measured in numbers (you’ve probably seen them on films – 100, 200, 400, 800 etc). The lower the number the lower the sensitivity of the film and the finer the grain in the shots you’re taking.
In Digital Photography ISO measures the sensitivity of the image sensor. The same principles apply as in film photography – the lower the number the less sensitive your camera is to light and the finer the grain. Higher ISO settings are generally used in darker situations to get faster shutter speeds (for example an indoor sports event when you want to freeze the action in lower light) – however the cost is noisier shots. I’ll illustrate this below with two elargements of shots that I just took – the one on the left is taken at 100 ISO and the one of the right at 3200 ISO (click to enlarge to see the full effect).
(you can see larger sized images of both shots here for the 100 ISO and here for the 3200 ISO)
Read more: http://digital-photography-school.co...#ixzz2GRKhTZVl
Digital "noise" is a common problem in digital cameras today. A lot of factors can introduce noise to your digital photography,[1] but there are certain steps you can take to avoid it, as noise can obscure detail and removing it from your images can take precious time.
Digital noise usually represents itself as speckled pixels of colour in your images or as a grainy effect, and is generally considered undesirable. Read on to find out how to reduce the chances that your valuable images will be affected by digital noise.
EditSteps
1. 1
Understand what a digital camera sensor is, and how it works. Unlike analog cameras, digital cameras work with a sensor instead of film. Sensors receive light and process it into electric charges via tiny photodiodes, whose outputs are reflected as pixels in your final digital image.[2] These electrical charges tell the sensor what colour each corresponding pixel is meant to be and other information which will create the digital image.
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www.acoustiblok.in
2. 2
Understand what digital "noise" is and what causes it. When light hits the sensor's photodiodes, a signal of electrons are produced in order to convey the light to the camera sensor. Electronic "noise" is the unwanted fluctuations in this signal.[3] In a digital camera, noise manifests itself as speckles, usually colored and patternless. These are generally caused by unwanted electron flow in and around the sensor adding to the desired electron flow. Noise can be caused by imperfections in the sensor itself such as "hot pixels"[4], randomness in the distribution of the limited numbers of photons available at low light levels,[5] and the sensor or camera overheating[6].
3. 3
Purchase higher-end, newer camera equipment. The most convenient, but expensive, way to combat noise is to buy a newer camera if yours is a few years old, with more expensive cameras being able to deliver better performance. Newer cameras have sensors that are developed to collect more light with less noise than those in older cameras, making them a good choice if you are struggling to control noise in your images and your gear is outdated.
o Choose a camera with a larger sensor. The problem with smaller sensors is that the light sensors are closer together than in a larger sensor, and that means the electrons overheating corrupt them faster due to their closer proximity. A larger sensor means that electrons will have to travel farther before corrupting their neighbouring light sensors. Full frame sensors are perfect for reducing noise in your images. A DSLR or large-sensor compact camera such as one in "Four Thirds" format is much better than a compact camera, even one a few years newer, although a full-frame DSLR is better still, as fast wide-angle and prime lenses for it are more widely available and cheaper.
o Pick a camera with fewer megapixels, or a lower resolution, in a given class. The more pixels there are on a camera's sensor, the closer they are together and the more likely overheating electrons will corrupt the light sensors. Although higher-end cameras generally have larger sensors with a high resolution or megapixel count, there are those which have larger sensors but still retain lower megapixel counts, making them perfect for dealing with digital noise.
o Pick a wide-aperture lens to maximize light intake. Some compact cameras have f/2.0 or f/2.8 lenses; a 50mm f/1.8 lens is inexpensive and excellent for a DSLR.[7] These will allow the same shutter speed at one-half to one-quarter the ISO setting of a common f/3.5 or f/4.5 maximum aperture zoom lens (At the same f/ratio, the bigger camera is still better: it's collecting equally intense light into bigger photosites, for far more photons to process. The absolute size of the aperture for a given angle of view matters more). Lenses are a much more mature technology than cameras, so an interchangeable wide-aperture lens will improve your photography through many camera upgrades. Image stabilization allows faster shutter speeds but tends not to be built into wide aperture lenses, making those better overall as they stop subject motion too; a fast lens and compatible in-body image stabilization is a great combination.
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Switch your camera's exposure to manual mode and adjust the settings which may introduce noise. When the camera is on automatic, or in program mode, as is the case with most lower-end cameras of the "point-and-click variety", your images are more likely to have noise as the camera changes the exposure by itself, and quite often it will introduce factors that introduce noise to your images. Taking control of your camera and exposure settings will help you eliminate factors which could contribute to digital noise in your photographs. Your camera's instruction manual will contain all instructions on how to adjust the various settings on your camera.
o It's OK to use a semi-automated exposure mode, but be sure to manually set a low ISO if possible. For instance, you could use aperture-priority mode with a wide aperture, which will allow a relatively short shutter speed with any given ISO. You could use your camera's exposure-compensation or bracketing function to try different exposures near the one the camera thinks is right.
o Reduce your ISO. ISO is the setting which controls how light sensitive your camera's sensor is. A lower ISO (for example ISO 200) means your sensor is less sensitive to light, but is also less likely to create digital noise, while a higher ISO (for example ISO 400, or ISO 800) makes your camera sensor more sensitive to available light, but also increases the chance your images will have noise. Check your camera's manual on how to adjust the ISO setting.
If you need a higher ISO for a correct exposure with a fast-enough shutter speed to avoid blur from a lack of camera support or moving subject, use it. Adding a few speckles of high-ISO noise is better than smearing the picture with blur or wiping out its shadow detail with underexposure.
o Use a faster shutter speed, or rather, avoid long exposures. Long shutter speeds (for example, exposures of 5 seconds, or 30 seconds or longer) create more noise as they make the camera's sensor overheat faster. Faster shutter speeds give less chance for the sensor to overheat. So consider adding more light to your image to reduce the exposure time, and reduce the chance of noise: turn on some lamps, or use a flash. If you can't add more light, or it would spoil the picture (like one of lights outdoors at night), a slightly slower shutter speed and a lower ISO will provide the best results, as described below.
o Increase your signal-to-noise ratio with a low ISO and generous exposure.[8] If you let a lot of light into your camera, preferably quickly, it will overpower the noise and give you an acceptable image. Use a low ISO setting, which amplifies the sensor's signals relatively little, and exposure to go with it (Some kinds of noise can accumulate over time, and even accrue more rapidly as the sensor warms through use, but a longer exposure is still generally better than a higher ISO). The lowest setting is usually best, but you'll usually have to look for noise to notice it up to ISO 400 with a compact camera or old DSLR, and up to ISO 1600 with a modern (2011) DSLR.
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Turn the camera's noise reduction setting on, if it has one. This feature is usually found in higher-end cameras. In-camera noise reduction is usually helpful in combating noise in your images, especially those of a longer exposure or in low light conditions. However be aware, it does smooth the fine detail in your images, making them softer to the eye, which can be problematic, so only use this setting if you feel that noise will a serious problem while shooting. PC software can often smooth noise in post production, while preserving detail better than that supplied in the camera's internal computer, and you can revert to your original image if you decide you didn't want so much smoothing, or even any at all.
o You can use "dark frame subtraction" – making a preliminary or subsequent "exposure" of the same length as the actual exposure but with the lens capped to detect noise to delete from the final image to compensate for "hot pixel" and other camera imperfection noise.[9] Some cameras can do it automatically, not bothering to open the shutter for the dark exposure, but you can perform it yourself, even with a compact camera.[10] This technique does not smooth your image, so is a suitable option for those who are worried about other noise reduction methods.
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Make your image as bright as possible. It may seem obvious, but the less shadow there is in your image, the less chance noise will have together there. Noise generally appears in darker areas of your images (where there's less light to overpower it), so whether you introduce a new light source, such as a lamp or flash, move to a better-lit area, change your exposure settings to allow more light or photograph lighter subjects, reducing the amount of shadow in your image will reduce the amount of noise.
o Night pictures can be tricky because the highlights are actually the light sources. Like the sun during the day, they're much brighter than the surrounding areas which receive and reflect back to the camera only a little of their light. A camera's light meter averaging their brightness with their surroundings as if they were ordinary highlights will underexpose them for one big, noisy over-dark shadow. Try increasing the exposure significantly over what it suggests.
o Very bright lights can cause streaking or "bloom" with the CCD sensors usually found in cheaper cameras. Try to avoid having them close-by in the image.
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Avoid using digital zoom, such as those frequently found on lower-end cameras or "point-and-click" varieties. Digital zoom is technically not zooming at all; it is in fact cropping and enlarging from a small area of the sensor. It should especially be avoided when that small area is clouded by noise.
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Keep your camera stored in a cool place before you use it. The cause of most noise is a thermal reaction. The warmer your camera is, the more likely the sensor will overheat in a shorter period of time. Making sure your camera is cool, especially when in hot conditions, can greatly improve your camera's performance and reduce the likelihood of digital noise. Excessive heat such as that in uninsulated areas of a car in the sun, will be harmful for cameras regardless.
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Take further steps to combat noise in post production, such as the aforementioned "dark frame subtraction" or noise reduction software. Sometimes, no matter what actions you take to reduce noise, it may still occur in your photos. In these cases you should take the time to learn and implement noise reduction in post processing.
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