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This weekly course covers the most common questions videographers encounter when shooting and editing with DSLR cameras, from choosing a frame size and frame rate to understanding moiré. Authors Rich Harrington and Robbie Carman will also help you understand the impacts of compression and the difference between cropped (or micro 4/3rds) and full-sized sensors in cameras, and much more. This continual FAQ guide is a handy way to find the answers to the questions that plague you the most.
Richard: A word that will come up a lot, especially for people that are starting to get serious about shooting DSLR video, is moire. And you're like oh, I want to avoid this. I hear it really damages the image. And I think that you know this is a real-world problem, but it's a lot like rolling shutter. You can shoot for a long time without ever seeing it. Robbie: Yeah, it certainly something to be concerned about but not something to be obsessed about or paralyzed over you know. The thing about moire is that it happens when we have tight overlapping pattern, right something like pinstripes in a shirt, maybe a screen door, tight brick patterns, carpet patterns, that kind of stuff.
And what it looks like is basically some vibrating of the actual image, right? And this happens again, just like rolling shutter, mainly because of how the sensors are working on these cameras, right? Richard: But it's not just CMOS sensors, I mean I remember back in the day when I was a Floor Director for a television news station, and I did the morning show. We would have guests on all the time, and it would be like, I'm sorry sir, could we hand you this nice off-white shirt instead of that tight pinstripe that you have. Robbie: Absolutely, this is I mean, that's like video production 101, right? You want to wear solid color versus tight patterns and something like that.
Richard: I'm sorry that tie is not legal for television. Robbie: Right. But it's exacerbated little bit by the CMOS sensors that are in use in these DSRL cameras. And the reason that is is because you can think about these sensors, right, they're pretty big, they're really big in fact because they were meant to take photos, right? You have these 20 megapixels sensors, but what we're doing when we're shooting videos we're going down to smaller portion of the sensor. So to do that-- Richard: Right, when we're taking 20 megapixels sensor and making it only capture about 2 megapixels. Robbie: Right, and to do that there's a whole bunch of fancy math involved.
But you know we don't have to bore people with. But there is issues like line skipping, meaning that not every, you know row of pixels is going to actually record in a part of the image, right? So, when you get in the things like line skipping and the math that's involved and sort of the interpolation that happens, because we're doing fancy math, guess what, there are errors, right? Richard: Yeah. Robbie: And some of those errors manifest themselves as moire patterns. Richard: Well, this happens even in still photos when you down-sample a high-res still to a lower-res image. Sometimes you'll see weirdness, or if you've ever had an image opened say in Photoshop, and you're looking at it at 25% magnification, it's like well that looks really weird, and then you go to 100%, you no longer see it. Robbie: Right.
Richard: Sometimes that down-sampling, especially when it's being done in the real time, leads to as you described image errors, and we see this with photos even. But it becomes worse in moving footage because you have--especially which is slight movement. So if I were wearing say an obnoxious tie, and I was just rocking back and forth-- Robbie: Which I've seen you in, by the way. Richard: Yeah, I have a few. If I rocked back and forth on camera you would see all this vibration happening. Robbie: Absolutely, it's movement, it's the angle towards the pattern, and you know the things of that nature, and that's why you know a lot of times that if you're going to be specially doing a narrative, something like let's say you're shooting a shot through a screen door, right? You know, you can still take that shot, right? But you need to be very careful about the angle and shots that you're shooting on to that screen doors to avoid the moire patterns.
Richard: All right. So now that we understand what it is, let's come back in a second and talk about how to fix it or avoid it altogether.
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