The Camera Image Buffer in Digital Photography

When you press the shutter button and take an image, the photo doesn't just magically end up on the memory card. Whether it's a fixed lens model, a mirrorless ILC, or a DSLR, the digital camera has to go through a series of steps before the image is stored on the memory card. One of the key components of storing an image on a digital camera is the image buffer.

The camera's image buffer storage area is important for determining the operational performance of any camera, especially when you're making use of a continuous shot mode.

Capturing Photo Data

When you're recording a photograph with a digital camera, the image sensor is exposed to light, and the sensor measures the light that strikes each pixel on the sensor. An image sensor has millions of pixels (photoreceptor areas)—a 20-megapixel camera contains 20 million photoreceptors on the image sensor.

The image sensor determines the color and intensity of the light that strikes each pixel. An image processor inside the camera converts the light into digital data, which is a set of numbers that the computer can use to create an image on a display screen.

This data is then processed in the camera and written to the storage card. The data in the image file is just like any other computer file that you'd see, such as a word processing file or a spreadsheet.

Moving the Data Fast

To help speed up this process, DSLRs and other digital cameras contain a camera buffer (consisting of random access memory, or RAM), which temporarily holds the data information before the camera's hardware writes it to the memory card. A large camera image buffer allows for more photos to be stored in this temporary area while waiting to be written to the memory card.

Different cameras and different memory cards have different write speeds, which means they can clear the camera buffer at different speeds. So, having a larger storage area in the camera buffer allows for storing more photos in this temporary area, which produces a better performance when making use of continuous shot mode (also called burst mode). 

This mode refers to the camera's ability to take several shots immediately after one another. The number of shots that can be taken simultaneously depends on the size of the camera's buffer.

While inexpensive cameras contain small buffer areas, most modern DSLRs contain large buffers that allow you to keep shooting while data is processed in the background. Original DSLRs didn't contain buffers at all, and you had to wait for each shot to be processed before you could shoot again!

Location of the Image Buffer

The camera buffer can be located either before or after image processing. 

• Before Image Processing Buffer. The RAW data from the sensor is placed directly into the buffer. The data is then processed and written to the storage card in a container format like NEF, CR2, or ARW in conjunction with other tasks. In cameras with this sort of buffer, continuous shooting cannot be increased by reducing the file size.
• After Image Processing Buffer. The images are processed and turned into their final format before being placed in the buffer. Because of this, the number of shots taken in continuous shooting mode can be increased by reducing the image file size.

Some DSLRs use "Smart" buffering. This method combines elements of both before and after buffers. The unprocessed files are stored in the camera buffer to allow for a higher "frames per second" (fps) rate. They are then processed into their final format and sent back to the buffer. The files later can be written to the storage cards at the same time as images are being processed, thus preventing a bottleneck.