Is it really that important? To get exposure right in the camera, after all, isn't one of the great benefits of digital photography the fact you can fix errors later in image processing software? Well, the answer is yes, and no minor adjustments to exposure can be made without too much effect on image quality, but more significant alterations. To leave you with the problem and to show you what that problem is, I'm going off to do some science. One of the roles of science is to find solutions to challenging problems. When I take a photograph, the shutter opens and light comes flooding into the camera. Now, using water to represent that light. Imagine is collected in the measuring cylinder, while the camera then has to do is decide how to distribute that light across the sensor so it represents the tones in my photograph. Those tones are represented by these test tubes. I'm using five test use. Just to simplify this particular experiment. Test tube on the right hand side of your white to...
nes. Next with the light greys medium, graze dark graze on the black tones over here on the left, the camera uses half of all the light it collected to create the white tones. To represent that, I'm going to fill this right hand, test you with white tones all the way through the top, because light greys are half assed bright as whites, the camera only uses half the amount of light. I'm going to represent that by filling the light grey test tube only half life the same for the medium grace off again. Same for the dark grays off as much again and the same for the blacks half assed much again. So what we can see here is that compared to the white tones, the black tones have very, very little light signal. Now, if I under exposed my photograph by just one stop, what happens is, rather than pouring all of that light into this right hand test tube, the camera simply discards it, and this is what we're left with. But that's okay, because we can fix under exposure in processing, right? Well, let's try it. A computer. What I'd now do is tell the software to take all of the light gray tones and turn them white. Let's replicate what I've just done in the computer using the test tubes. Well, I've got to do is I've got to try and fill up this empty right hand, test you all the way to the top using only the information available in the other test tubes without losing any of that information. So let's give it a go. If I take the light gray tones, you can see where I'm going with this, right? It doesn't take a rocket scientist to work out. It simply can't be done. What actually happens to the photograph when you do this for real is this you see from the history, Graham. There are now large areas of missing data, which all these gaps and this will show on your images. Banding which areas of distinct tonal variation where you can tell where one tone starts on another ends no good. Now you may have heard the term exposed to the right. What does that mean? Well, to answer that question, let's head back to the science lab. Let's go back to the test use on. Don't worry, it's the last time. This is what my correctly exposed image looks like. We've already seen the effects of under exposing why one stop this time, I'm going to expose for the lighter tones by one stop. What happens now is the camera discards the information in the black tones to fix this in photo shop or in the computer. What I do is I go to the Levels Adjustment tool, and we can look at the history am here and see that it's skewed over to the right hand side. Well, I'm going to do now is going to tell the computer to take all of the dark gray tones and make them black. This time, if I replicate what I've just done in the computer with the test tubes, you can see that there's so much light over here in the right hand side that it's simple to replace a little bit missing in the black tones. So in digital photography, the mantra is exposed for the brightest part of the scene, where detail is important