Rolling shutter

The rolling shutter effect is a position error in images that can occur by a technical phenomenon in the row or column-wise photographic recording of moving images. The term comes from English and means translates as " rolling shutter ".

Explanation

It initially appears to be understood that the exposure of all the points of the photosensitive member ( or film ) sensor of a camera starts at exactly the same time. There are cameras in which the type of construction does not apply to the whole area; there has to be more like a ' line simultaneous exposure starts " imagine the line by line or column by column travels either via the element for which it requires a short while only, but non-negligible time.

As long as the subject is motionless, all pixels are also used in such cameras exposed to their correct position, regardless of when the corresponding points were exposed. However, when shooting a moving subject, or taken with a moving camera, with successively exposed lines, objects are mapped to their current location - and since the image line by line, the object has already moved so far from one to the next line, that in composition all the lines is an object for display, which is not shown as a whole at one time, row by row but at different times. A straight line of the subject can be imaged crooked or distorted while panning or a moving subject (corresponding to the successive individual rows).

Technically, there is for the rolling shutter effect for two reasons:

• For digital cameras, it typically occurs in image sensors in CMOS sensor technology, since they allow only a row- or column-wise signal processing in the rule.

• All cameras whose exposure technique is based on a focal plane shutter, show the effect. He enters this becomes particularly evident when the subject is illuminated with a stroboscope.

High-resolution camcorders and video-style digital cameras are increasingly equipped with CMOS image sensors, replacing the formerly used CCD sensors. Due to the CMOS image sensor, it can come to occurrence of the rolling shutter effect in these devices. As with the photograph of this effect occurs by diagonal distortion when shooting fast-moving subjects in appearance, also lead stronger vibrations of the recording device, such as occur for example when shooting from a vehicle to a strong distortion of the entire image, allowing the recording may be unusable.

Avoidance

Can be avoided the rolling shutter effect with the so-called global shutter CMOS sensors, which are not in rows and columns of the image, but completely absorb. CCD sensors virtue of their other operation no rolling shutter effect.

Illustrative examples of

Simulation

In the pictures below, a camera pan to the left is ( the subject moves to the right ) while recording a vertical green line from bottom to top with three consecutive lines shown schematically:

At a higher number of rows corresponding to the steps and cracks are small, so that in the limit, a continuous oblique line would be produced.

Flatbed Scanner

The following two pictures were taken one by one with the same flatbed scanner with line sensor. The first frame, the paper template was unmoved, and the second image the template at a steady rate was moved perpendicular to the direction of the scan unit, so that the rolling shutter effect is visible.