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Let's take a look at some of the practical issues concerning digital files, right at Capture, right on the camera shutter is pressed. Now Keep in mind that as a digital file takes it's journey from capture, to edit, to output, some data is lost at each step along the way. So it follows to having the absolute best digital file to start, is important to ensure that the best file result possible is received. Because of the need for the best possible initial file, it's important for the photographer to shoot in Raw, not JPEG. There are 3 ways that Raw is clearly superior to JPEG files: bit depth, compression, and original data protection.
So let's take a look at some of the limitations that JPEGs have. Now Bit Depth means, how many steps are available from light to dark for each colored channel in a digital capture. Our camera capture in 3 channels, RGB or red, green and blue. Now a JPEG file, has a maximum of 8 bits of total data per channel. That means there are 256 steps available from light to dark. Now in a 16 bit file, which was what a raw file can work in, there are theoretically, 65,536 steps from light to dark.
Now the best current DSLRs can capture maybe 14 bits, which is maybe 16,000 plus steps. But all these numbers are wonderful, but how does it affect your file? Bit depth becomes an issue, when you start editing an image. As I mentioned, every time you perform an adjustment, data is moved, combined or lost. Having a full 256 steps in an SRGB Jpeg will produce a great print from your Photolab, but after the editing process, you no longer have those 256 steps.
But, take a look here at the histogram in the lower right. It's a nice full graph. We've got data from black almost up to the pure white. There's no holes in it. That means we're going to get a nice print. However, if you take a look at a histogram of an 8 bit file that has had a lot of editing done to it. You'll see there are breaks and holes that start appearing in the graph. The output result of these breaks is banding and color gradations. And each time you edit a JPEG and resave it, you continue to lose data.
After a couple of rounds of editing a JPEG file, you've lost detail and color fidelity. And started to introduce compression artifacts. You can see here that the shadow detail, has been lost and that there are color shifts in the clouds. Now, when you start with over 4000 steps in a 12 bit file, or more with a 14 or 16 bit file, you can do some serious editing and lose a lot of those steps. Let's say you've got a 12 bit file and have done so much editing that you've lost 75 % of the original data in this case, you still have 1,000 steps from light to dark.
And when you convert this file to that SRGB JPEG, it will take the best 256 steps available from those 1,000 that you were left with. So, you're back having a full 256 step file in a nice, full histogram without any holes in it. And this means you're going to get a really good print and not have to worry about these artifacts or loss of detail, the next part is compression. JPEG files by definition are compressed files. They do this by averaging the data in nearby pixels to cut down on file size.
You've probably seen badly compressed JPEG files, where you start to see big squares. Each time you open, edit and save a JPEG file, the file is recompressed and more detail and color data is lost. Now if you work with a raw file, that means you'll always have the full amount of ream of data. Lets take a closer look and see what happens to this jpeg's that keeps getting resaved. You've probably seen this before, particularly with images viewed on a web. As that JPEG file continues to be resaved and at lower quality settings you'll start to see these compression blocks become noticeable.
Not a pretty site if you're after a quality viewing of your images. Raw files are uncompressed data files. That means that there are red, green, and blue numbers for each and every pixel in your image. When you edit a raw file in Adobe Camera Raw, Lightroom, or another Raw editor, you're not actually changing any data in that raw file. What you're doing is assigning a set of adjustments that will be made to the raw data when it is opened in your editing software. The original raw file is untouched, means it's always there, it's always safe and you can always go back to it.
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