How exposure affects noise levels - Photoshop Tutorial

- [Instructor] Digital noise is often a fact of life in photographs taken with higher ISO settings under night or low light conditions. Before we get into how to reduce noise on images that you've already shot, let's take a look at ways that you can minimize noise by ensuring that your images are well exposed. Since noise tends to be more noticeable with higher ISO settings, one way to reduce the need for a high ISO is to use a tripod for night or low light shooting. This will allow you to use a lower ISO. The compromise of using a low ISO at night, however, is that you'll have to rely on much longer shutter speeds. So, for example, in this shot here of my snowy back yard at 2:30 in the morning, my first shot was ISO 1000 with an exposure time of 30 seconds. And this was on a tripod. Next, I lowered the ISO to 200, but that meant that I had to compensate by increasing my exposure time, or my shutter speed, to about two minutes. And as I go back and forth between these two shots, you can see that the overall exposure, or the brightness of the scene, is essentially the same in both versions. The main difference is the exposure time. Now, in order to really see what noise is doing in an image, you have to zoom up close, and it also helps to pay attention to the darker underexposed areas since that's where the noise will be more visible, and in some case more objectionable, especially if you want to lighten those areas. So, to check this out on this scene, I made a version that was way too bright but it allowed me to see what was happening in those darker shadow areas, and if we compare the two shots, you can see that the ISO 200 shot on the right hand side has much lower noise level than the ISO 1000 shot. Now, as long you're not photographing subjects where stopping motion is important, then using a tripod and longer shutter speeds may be a viable approach to minimize noise in your photographs. But, if a tripod is not an option, or you just don't have one with you, then you'll have to venture up into the land of higher ISO settings. In this case, paying close attention to the exposure can help to minimize the noise. To explore this, we'll take a look at these three shots of an outdoor lounge at a nightclub. Let's dive into Adobe Camera Raw so we can see these in more detail. So these three shots were all taken with the same ISO 1000 and also the same lens aperture. The big difference was the exposure timer, shutter speed, and you can see that listed here underneath the histogram. So for the first one, it was 1/5 of a second, then 1/3 of a second, and finally 1.3 seconds and since these were all handheld shots, you can see on this last one it's kind of blurry. What I want to do is I want to lighten up all of them to about the same level so we can really see what's happening with the noise. So I'll come to the Exposure slider and just really brighten that up a lot, and I'll come to the second one and do the same thing. Again, this is just an adjustment so we can see into the shadows. It's not something that I feel is a good adjustment. And finally, let's come down to the last one which doesn't need much brightening, something like that looks pretty good. So, here's a cool Camera Raw trick. If you select all of these by clicking on the first one, and then Shift-clicking on the last one, you can then zoom them all to the same level. So I'll come to the Zoom menu and choose 100, and if I get the Space bar to get the grabber hand, I can also adjust them to where they are at the same level. So, let's look at these in order. So this is the one with the shortest exposure time, 1/5 of a second. You can see that there's quite a lot of obvious noise there. Then we come to the one that was a third of a second. The noise is definitely better, especially on this carved entry portal there. And then finally, if we go to the one that was 1.3 seconds, you're going to see much better noise levels. It's a much smoother, more creamy level of noise here on the yellow wall and in the curtains. Knowing how exposure affects noise levels will not minimize the base noise level that's created by a certain ISO setting, but having a well-exposed shot will yield better noise levels overall and can prevent the shadow areas from becoming too noisy, especially if you need to lighten up the image as we saw in this example. Even if shooting on a tripod is not an option, see if you can stabilize the camera by bracing it against something so that you can use either a lower ISO setting or a longer shutter speed for increased exposure.