After the sensor is exposed, the image data will be processed in the camera and then written to the storage card. A buffer inside a digital camera consists of RAM memory which temporarily holds the image information before it is written out to storage card. This speeds up the "time between shots" and allows burst (continuous) shooting mode. The very first digital cameras didn't have any buffer, so after you took the shot you HAD to wait for the image to be written to the storage card before you could take the next shot. Currently, most digital cameras have relatively large buffers which allow them to operate as quickly as a film camera while writing data to the storage card in the background (without interrupting your ability to shoot).
The location of the buffer within the camera system is normally not specified, but affects the number of images that can be shot in burst mode. The buffer memory is located either before or after the image processing.
After Image Processing Buffer
With this method the images are processed and turned into their final output format before they are placed in the buffer. As a consequence, the number of shots which can be taken in a burst can be increased by reducing image file size (e.g. shoot in JPEG, reduce JPEG quality, reduce resolution).
Before Image Processing Buffer
In this method no image processing is carried out and the RAW data from the CCD is placed immediately in the buffer. In parallel to other camera tasks, the RAW images are processed and written to the storage card. In cameras with this type of buffer, the number of frames which can be taken in burst mode cannot be increased by reducing image file size. But the number of frames per second (fps) is independent of the image processing speed (until the buffer is full).
The "smart buffering" mentioned by Phil Askey in his Nikon D70 review, combines elements from the above two buffering methods. Just like in the "Before Image Processing Buffer" the unprocessed image data are stored into the buffer (1) allowing for a higher fps. They are then processed (2) and converted into JPEG, TIFF or RAW. But instead of writing the processed images to the storage card they are stored in the buffer (3). Therefore, the image processing is not bottlenecked by the writing to the storage card, which happens in parallel. Moreover, it constantly frees up buffer space for new images since (3) takes up less space than (2), especially in the case of JPEG. Just like in the "After Image Processing Buffer", the output images are then written from the buffer to the storage card (4). But an important difference is that here the image processing happens in parallel with writing to the storage card. So the image processing of new images can continue while the other images are being written to the storage card. This means that you do not necessarily have to wait for the entire burst of frames to be written to the CF card before there is enough space to take another full burst.
This article is written by Vincent Bockaert,
author of The 123 of digital imaging Interactive Learning Suite
Click here to visit 123di.com