I’m not, @thebecker gave me homework from the @thebschool to think about what I’m great at and try and share that with someone that’s just good at it. And since I don’t know who just good at it, I thought I would start here. So I said to myself, self what are you great at? So I began to think and think and think….and I came up with this. I received my bachelors of Electrical Engineering from Arizona State University (GO DEVILS!!!) with a specialization in advanced optics and image processing. I worked in the field for 10 years for some of the largest defense contractors in this country. Working on some of the most advanced weapons systems the world has ever seen or may never see. All for one simple reason….to give our neighbors, their kids, their grand kids, nephews, nieces, friends, moms, dads and whoever else that had to be in harms way, for reasons right or wrong, the chance at coming home to their loved ones; by providing them with only the best we as a country have to offer. That being said I have learned my fair share of the physical limitations of an optical system in and out. So although I don’t feel great as @thebecker asked for, I do feel I have something to offer my fellow photogs, and this post will be just beginning.

RAW or JPEG

There seems to be a lot of confusion among some new digital camera owners about exactly what the difference is between RAW and JPEG files. Lets shed some light on the subject, pun intended:)

First some basics

The digital sensor in the majority of digital cameras is what is known as a BAYER PATTERN sensor. This relates to the arrangement of red, green and blue sensitive areas. A typical sensor looks like this:

Each pixel in the sensor responds to either red, green or blue light. There are 2 green sensitive pixels for each red and blue pixel. Why are there twice as many green you might ask, because the human eye is more sensitive to green, so the green channel is the most important. For the same reason night vision goggles almost exclusively represent data to the user as green intensities, not because the military like’s green:) The sensor measures the intensity of the corresponding color light falling on it. The green pixels measure the green and so on. The readout from the sensor is in units of intensity for each individual pixel, where color can be red, green or blue and for a Canon 1Ds Mark III or Canon 5D Mark II 14 bit sensor these values range from 0 to 16384 (2^14).

A conventional digital image has pixels which can be red, green, blue of any one of millions of other colors, so to generate such an image from the data output by the sensor, a significant amount of signal processing is required. This processing is called Bayer interpolation because it must interpolate what the color of each pixel should be. The color and intensity of each pixel is calculated based on the relative strengths of the red, green and blue channel data from all the neighboring pixels.

RAW data

RAW data is the output from each of the original red, green and blue sensitive pixels of the image sensor, after being read out of the array by the array electronics and passing through an analog to digital converter. The readout electronics collect and amplify the sensor data and it’s at this point that “ISO” (relative sensor speed) is set. If readout is done with little amplification, that corresponds to a low ISO (say ISO 100), while if the data is read out with a lot of amplification, that corresponds to a high ISO setting (say ISO 6400). All electronics generate some level of noise simply based on physics. Therefore, the sensor is more susceptible to collecting this readout noise while the sensor is more sensitive (i.e. high ISO). So the “grain” in those high ISO images is a result of your cameras electronics being noisy.

So, you really have two choices with what to do with your RAW images; save them on the memory card or allow the cameras internal image processor to convert them to JPEG (Joint Photographic Experts Group).

If the data is stored as a JPEG file, it goes through the Bayer interpolation, and is then modified by in camera set parameters such as white balance, saturation, sharpness, contrast etc. and compressed and quantized according to the JPEG standard and stored on your memory card. For obvious reasons JPEG is a good option for most, smaller file size means fast data transfer to the memory card and of course more images on that card. The disadvantage is that there is a quality loss, the amount of loss depending on how much compression is used.

Since it’s on a PC you can now pick whatever white balance, contrast, saturation, sharpness etc. you want. So here’s the first advantage of saving RAW data. You can change many of the shooting parameters AFTER exposure. You can’t change the exposure (obviously) and you can’t change the ISO, but you can change many other parameters.

A second advantage of shooting a RAW file is that you can also perform the conversion to an 8-bit or 16-bit TIFF file. TIFF files are larger than JPEG files, but they retain the full quality of the image. They can be compressed or uncompressed, but the compression scheme is lossless, meaning that although the file gets a little smaller, no information is lost. This is a tricky concept for some people, but here’s a simple example of lossless compression. Take this string of digits:

12345555555556789

Is there a way to store this that doesn’t lose any digits, but takes less space? The answer is yes. One way would be as follows

12345[9]6789

Here the string 555555555 has been replaced by 5[9] – meaning a string of 9 5s. You’ve stored the same exact data, but the “compressed” version takes up less space. This is similar (but not identical) to the way lossless TIFF compression is done.

I said above that the data could be stored as an 8 or 16-bit TIFF file. RAW data from most high end digital camera contains 14 bit data, which means that there can be 16384 different intensity levels for each pixel. In an 8-bit file (such as a JPEG), each pixel can have one of 256 different intensity levels. The answer is that it allows you to perform a greater range of manipulation to the image without degrading the quality. You can adjust curves and levels to a greater extent, then convert back to 8-bit data for printing. If you want to access all 14 bits of the original RAW file, you can convert to a 16-bit TIFF file. Why not a 14-bit TIFF file? Because there’s no such thing! Actually what you do is put the 14-bit data in a 16 bit container, sort of like pouring a can of soda into a 2 liter bottle, you get to keep all the liquid but you have some free space. Putting the 14 bit data in a 8 bit file is like pouring that can of soda into a shot glass. It won’t all fit so you have to throw some away.

So do I shoot RAW or JPEG?

You shoot RAW for flexibility, flexibility, flexibility. If you’re not sure about exposure or white balance, or if you want to maintain the maximum possible allowable post exposure processing, then you’ll want to shoot RAW files. You shoot JPEG if good enough is good enough. Both are acceptable, there is no right answer; just do what works best for you and your needs.

Of course there are plenty of mathematics to verify this, but it’s boring to most, and I don’t want to bore anyone. If you would like more info please feel free to contact me at @BradtPhoto on twitter. And stay tuned for more technical discussions that can help you make sense of your equipment and why we do what we do.