When shooting strong source of ligh with a compact camera with a CCD sensor it will often have 'blooming': white (or purple) vertical stripes. They are recorded in video, but not in still images.
Does anybody know a clever way of getting rid of blooming in post?
EDIT:
A little further investigation reveales that the vertical line isn't a blooming effect, but actually a readout effect. Blooming is still an issue with oversaturated pixels, and you can see it as small vertical burnt out lines around very bright parts of the subject, even in the final shot. The full height vertical lines on preview and movie mode are due to the manner in which the image is read out, and the lack of any shuttering when in these modes. Movie and preview simply let the light shine on the sensor, even during readout. They depend upon the ability of the sensor to read out the entire image in a short enough time that the impinging light does not noticably affect the wanted image even though the pixels are being shunted along the columns during readout.
For those that don't know, a CCD is called a charge coupled device because of the manner in which it shunts buckets of charge along a line of buckets. A CCD sensor uses this mechanism to read the sensor by having one line of buckets that shunts a row of pixels off the sensor to be converted to digital values, and then that line is filled with the next row of pixels in one step by shunting every column by one pixel - dumpling the charge from the next row into the line readout line of buckets. The readout line runs very fast, but clearly the time to shunt the entire set of columns is much slower. All the time this is happening the image on the sensor is slowly being moved up the sensor towards the readout line. During this time, any new light impinging on the sensor will continue to be converted to charge, and will add to the charge in the bucket under the sensor - even if that bucket is really from a sensor element elsewhere in the column. So long as the light intensity isn't too great and the readout speed is fast enough you get away with it. But clearly if there is a very bright point in the scene you will get a problem. And that spot causes a trail along all of the pixels in the column. Another limit is that the faster the buckets are read out, the more noise there is in the readout process - because the analog to digital converter does not have enough time to resolve as much. So it is all a balancing act.
Does anybody know a clever way of getting rid of blooming in post?
EDIT:
A little further investigation reveales that the vertical line isn't a blooming effect, but actually a readout effect. Blooming is still an issue with oversaturated pixels, and you can see it as small vertical burnt out lines around very bright parts of the subject, even in the final shot. The full height vertical lines on preview and movie mode are due to the manner in which the image is read out, and the lack of any shuttering when in these modes. Movie and preview simply let the light shine on the sensor, even during readout. They depend upon the ability of the sensor to read out the entire image in a short enough time that the impinging light does not noticably affect the wanted image even though the pixels are being shunted along the columns during readout.
For those that don't know, a CCD is called a charge coupled device because of the manner in which it shunts buckets of charge along a line of buckets. A CCD sensor uses this mechanism to read the sensor by having one line of buckets that shunts a row of pixels off the sensor to be converted to digital values, and then that line is filled with the next row of pixels in one step by shunting every column by one pixel - dumpling the charge from the next row into the line readout line of buckets. The readout line runs very fast, but clearly the time to shunt the entire set of columns is much slower. All the time this is happening the image on the sensor is slowly being moved up the sensor towards the readout line. During this time, any new light impinging on the sensor will continue to be converted to charge, and will add to the charge in the bucket under the sensor - even if that bucket is really from a sensor element elsewhere in the column. So long as the light intensity isn't too great and the readout speed is fast enough you get away with it. But clearly if there is a very bright point in the scene you will get a problem. And that spot causes a trail along all of the pixels in the column. Another limit is that the faster the buckets are read out, the more noise there is in the readout process - because the analog to digital converter does not have enough time to resolve as much. So it is all a balancing act.