What is the digital counterpart to graininess in traditional photography and what is its cause?

Question

Extra points.

Answer 1

Noise. But contrary to what people here are saying, more pixels does not equal less noise. In fact, higher pixel density on the sensor can lead to more noise. Large, low-pixel-count sensors are often virtually noise-free. Point-and-shoot style digicams are noisier than DSLRs for this reason; while they have a comparable number of pixels, their sensors are much smaller.

Noise is caused by lots of things, but a few factors are heat (which is why commercial digital cameras used to have elaborate cooling systems), and gain (as in amplifying a signal in low-light situations).

Answer 2

Graininess in traditional photography is caused by size of the chemical particles on the film or paper. Slow speed / lower ASA film / paper use fine particles and very closely knit structure. High speed / higher ASA film /paper is made of bigger particles and scattered structure. The graininess is visible on film / paper when under exposed or under developed image or enlarged image from the actual exposed image.

In digital photography many factors caused graininess of any image, which is called as pixelation.

The physical size of CCD and the active number of pixels on that CCD will decide the vertical - horizontal dimensions of an image at resolution of 72 Dots Per Inch.

When such an image is increased in dimensional size then the pixelation is noticeable.

Example is 3 m. p. 1/4" CCD has a Width - 72.25, Hight 54.19 cm at 72 dpi resolution image.

If such image is displayed on computer screen at same dimensions, it will not cause any pixelation. but enlarged than original will cause pixelation.

Same image at 300 dpi resolution for printing on paper will have W17.34 and H13 cm. size. If increased to W25, H 20 will cause pixelation.

One more factor for graininess is low light or dark area of an Image will show noise at enlarge sizes.

Answer 3

actually all the answers given are wrong. the "grain" of low light digital cameras is an artifact of the CCD sensor array. At very low light levels, the dark current of adjacent CCD pixel elements differs slightly. this is an unavoidable defect in the ccd manufacture process. so when you compensate for low light by increasing the electrical amplification (gain up or ISO selection) the darker area of the picture shows a pattern that is reminiscent of film grain. it is not random noise. in fact for a video camera, successive frames will have the same pattern, so that it eventually looks like you are shooting through a window screen. more pixels does not eliminate patterns, but may allow you to blur out in photoshop without sacrificing too much picture sharpness.

Answer 4

Pixels, a low number of pixels causes the photo to be grainy. Look for cameras with 6 or 8 mega pixels. The more pixels you have the finer the grain.

Answer 5

It is caused noise.

Digital cameras convert light, an analog signal, in to digital signals through it's image sensor and analog to digital converter. Light coming through the lens strikes the image sensor , which is comprised of (usually) millions of tiny photoreceptors. Each photoreceptor reads the incoming color and intensity of the light and converts it to a digital binary signal.

Noise is the result of tiny variations or imperfections in this analog to digital conversion process. Each photoreceptor itself will have slight variations each time you take a photo. Also there will be slight variation from one photoreceptor to it's neighboring photoreceptor which will result in slight color variations. Normally these very slight variations are hardly noticeable, but noise can be increased (or lessened) depending on some certain variables:

1) ISO - Digital cameras have an ISO setting which basically increases the amplification of the camera's image sensor to read and convert light data. Increasing the ISO setting allows a photographer to shoot under lower light conditions. This is very similar to ASA for film - the higher the number, the more sensitive to light. Increasing the amplification of the image sensor increases noise. Think of it as turning up your radio volume to hear a weak signal - you can hear the signal but you also introduce a lot of "hissing" noise.

2) Heat can cause noise. Heat-generated electrons can make their way to the photoreceptor and affect the digital output. Long exposures on your camera creates sensor heat and increases noise.

3) The overall size of the sensor itself can be a factor of noise. Each photoreceptor creates electrical noise which can contaminate it's neighboring photoreceptor. The larger the sensor, the further away each individual photoreceptor can be from it's neighbor. Also larger sensors can accomodate larger individual photoreceptors. Larger photoreceptors have lower signal to noise ratios and thus less noise. Digital SLR cameras have generally larger photo sensors than consumer compact cameras and usually have exhibit less noise. Contrary to what some said above, packing more and smaller photoreceptors on a digital sensor (i.e. increasing megapixels without increasing the overall size of the digital sensor) actually increases noise.

That's about all I can think of regarding noise variables....

Cameras also have in-camera noise reduction, which is an algorithm built in to the camera's processing to detect and remove the noise created from the sensor. Extra noise reduction kicks in under high ISO settings or long exposures. There are also several software programs which can effectively reduce noise in an image. Both in-camera noise reduction and software-based noise reduction attempt to decrease noise that is already generated from the sensor. Some companies are better than other at accomplishing this.

Hope that helps.

Answer 6

It's called noise.
It's usually only objectionable at higher ISO. I am not an engineer, so I am not going to attempt a scientific explanation :-)

Answer 7

Pixels. The more pixels in the picture the finer it is.