WHAT REALLY IS ISO?

ISO is an English equivalent acronym for the International Organization for Standardization.

Back in the days of film, its sensitivity to light was stated as ISO / ASA, with the value of 100 as "standard" for daylight (daytime) use. The higher the ISO value, the more sensitive the corresponding film is to light, which would allow for the use of a smaller lens aperture, or faster shutter speeds.

When film got "replaced" with the camera's digital imaging sensors of today, the ISO film standard was retained, as a basis for determining the equivalent of the light sensitivity settings of the imaging sensor.

Digital Camera ISO is basically an amplification system for the light signal recorded by the camera’s imaging sensor, giving the equivalent (and often perceived) effect of increased sensor sensitivity.

Adjusting to a higher ISO value would, therefore, allow an image to be taken even under low lighting conditions, without the use of flash or other additional light sources. It can also mean that you can use faster shutter speeds to freeze action that would otherwise have been impossible under the prevailing low lighting conditions.

However, the downside of amplification with high ISO settings is a corresponding increase in digital image noise, shown as grainy, random speckles of colored, unrelated pixels that decrease the image quality of the resulting pictures. 


In order to preserve image quality, the ISO value should only be increased when absolutely necessary. This means that high ISO settings are not always used in the lowest lighting conditions – in fact, when using flash or a tripod, it would be usual to use the lowest ISO settings, such as ISO 80 or 100, to maximize image quality.

VERTICAL STREAKS IN THE PICTURE AREA: CCD BLOOMING

The characteristic VERTICAL (often violet) light streak that you see when pointing the camera at very bright sources of light is called 'blooming.'

Blooming occurs when the electrical charge in a pixel exceeds the saturation level (due to very bright light) and the charge starts to fill adjacent pixels in the camera's digital imaging sensor. Typically CCD sensors are designed to allow for easy VERTICAL shifting of the charge but potential barriers are created to reduce flow into horizontal pixels. Hence the excess charge will preferentially flow into the nearest VERTICAL neighbors, resulting to blooming. 

Recording the image (as a still picture) is a different matter, for it occurs only at a very short period of time, usually at a fraction of a second, and does not get a continuous light reading (unlike when recording video). Therefore, there is no saturation of the pixel charge. This is the reason why the vertical violet streak (blooming) DOES NOT APPEAR in the recorded image of your pictures, but does, indeed, appear when taking video clips.

Blooming is an inherent characteristic of Charge Coupled Device (CCD) sensors, which is the type used in the GE X5 / X500, and is something that GE X5 / X500 users would have to live with.  Cameras, such as most of the dSLRs, make use of CMOS sensors, which are, by their nature, immune to blooming.