Digital File Formats

A couple of us were chatting in the pool recently while waiting for a youth group to get ready and the topic of UW photos can up and I mention the file format RAW.
I felt I may have lost some in translation.

Here’s a simplistic description of how your digital camera works. You press the shutter release and light from the image you’re photographing shines on a digital sensor (instead of film). That sensor consists of a grid of pixels that capture the image and store it on whatever digital media (e.g., memory card) you put into your camera.

Every manufacturer’s sensor has its own digital format. That’s the sensor’s RAW format. If you’re shooting RAW, all that means is that the sensor stores the image in its own proprietary format on memory.

What’s the alternative? You could configure your camera to store the image in a standard format like JPEG. Not all cameras let you shoot RAW. Lower end cameras don’t give you the option; they’ll store the image in JPEG. The sensor shoots whatever RAW format it uses, but the camera converts the image to JPEG before storing and only gives you options about image size and compression (more about this later).

What’s the big deal? Well, two things. First, since the sensor is storing its proprietary RAW format, it’s fast. Second, ALL the image information from the sensor is stored in memory. You haven’t lost any information. By the way, that also means the image is BIG. For example, a 12 megapixel RAW format runs about 11 megabytes. That’s big!

RAW is also proprietary, meaning you need software from the manufacturer to read and manipulate it. many manufactures provide a free software package you can download to your PC to read their RAW format and convert it to JPEG or TIFF. Some software packages include RAW readers for major manufacturers (MAC’s iPhoto and Aperture software packages read RAW).

Once you’ve edited your picture, you’ll probably want to share it. That’s when you convert it to a standard format. JPEG is the most popular because it’s not only standard, it also compresses the image to make it less painful to post on a web page or e-mail. Any software package can open JPEG.

JPEG compresses your file by comparing successive pixels of your image and deciding whether a series is close enough to just store the information once and copy. More compression means greater differences are ignored; you get a smaller file but you lose image quality. You can also compress the file by reducing the pixel count (less megapixels). When you’re saving your image, your software will give you a dialogue box that gives you both options (image size and quality).

Want to preserve ALL your image quality but still have a standard format? The most popular is TIFF but TIFF is BIG. A 12 megapixel image that runs about 11mb RAW runs about 30mb TIFF!

So, to summarize. All digital camera sensors shoot RAW. Lower end cameras convert RAW to JPEG and give you options about image size and compression so you can trade image quality for storing more images on a given memory card. Higher end cameras give you the option of storing RAW for faster storage and highest quality images, but you need to make sure you have software on your computer that will read and process RAW.