What's the difference between RAW and JPG image formats?

RAW format

First, we need to clear something up: there's no single RAW file format. There are probably hundreds of different formats that all might end up being called RAW.

In short, RAW format captures the raw, unprocessed data from your digital camera. And by raw and unprocessed, I mean the data captured by the photo sensors in your particular model of camera - and as it turns out, those might not even be in what we consider as a standard "pixel" form yet.

As each camera's technology is different, so too is the data that it might save into a RAW formatted file. Different camera use different sensors which capture light and color in different ways. The RAW format records that data in as close to its original form as possible. But that means that what appears to be a single "raw" formatted file could still be unique to any of the hundreds of different camera makes and models that there might be.

RAW format is not typically compressed, but even when it is, it typically is a larger format due to the fact that is simply contains much more data about the image.

JPEG format

JPEG, or often just jpg (still pronounced "jay-peg"), is a standard file format that contains an encoded and compressed image.

JPEG itself stands for the Joint Photographic Experts Group, which created the specification for this standard format.

JPEG is what's called a "lossy" format. It uses the characteristics of the human eye, as well as the characteristics of photographs to actually remove some clarity from the image in order to achieve its compression.

Because conversion to .jpg format actually reduces the quality or "fidelity" of the image, it's not appropriate for all situations, but it is particularly adept at providing a very high degree of compression on photographs before the effect becomes noticeable by most people.

JPEG format has become a defacto standard for digital images and photographs, and can be produced by almost all digital cameras, manipulated by almost all digital imaging software, and can be read and displayed on nearly all computers.

RAW versus JPEG

If JPEG is so ubiquitous and (apparently) "good enough" that most people would never notice, why would we ever want to save in anything else?

Two reasons come to mind:

• To at least save and archive photographs in the highest fidelity and in a form as close to its original as possible. Somewhat like saving your old photograph's negatives.

• To be able to manipulate aspects of the photograph that can only best be manipulated in raw form. Somewhat like adjusting the image when making a print from that negative.

That last point deserves a little more discussion, as it's perhaps the most important to those who care.

For example, a RAW image format might save information that captures the camera's exposure setting at the time that the photo was taken. Additional RAW data within the image than might allow you to (within limits) actually manipulate the effective exposure as it's processed - perhaps correcting for an under- or over-exposed photograph. While the same effect can be simulated somewhat by playing with brightness and contrast on a processed photo such as a .jpg, the quality of the result is typically significantly better if the operation can be performed on the raw image.

Which should you use?

If you're a casual photographer, JPEG's probably just fine. The pictures that you take can be immediately shared with anyone and viewed anywhere without any additional work on your part.

On the other hand, if you're a photo buff planning to tweak your photos in programs like Lightroom or Photoshop, or if you just want to archive the highest possible quality image, then raw might be the appropriate choice. Do realize however that unless your camera can save in both RAW and JPEG at the same time (some do), that you'll need to process your RAW files into JPEGs in order to share them with others. That, in turn, will require software that understands the RAW format used by your camera.

What do I do?

I've dabbled in photography for years - longer than computing, actually. So I'm definitely the kind of person who wants to be able to not only save those images in the highest quality possible, but I play with 'em before I post 'em. I'll adjust color and exposure and crop and whatnot - much like I did back in my darkroom days.

So I have my camera save all my photographs in RAW format.

It's so much less messy than that old darkroom.