Photography Tips: EXPOSURE / Histogram - Filmmaking Tutorial 11


Uploaded by polcan99 on 15.10.2010

Transcript:
Welcome to another filmmaking tutorial. My name is Tom Antos.
Today I’m going to talk about getting the right exposure.
You could use a light meter, which... you know, they are great,
but they don’t always work, if you have a lot of things,
for example, in front of your lens. Things like, for example, a variable ND filter,
which will basically throw off all your calculations. And also, they’re expensive.
Now, a lot of cameras have built-in light meters, so you can use that as well.
But personally, I don’t think it works all that well in a lot of these situations
that I find myself in. So, if you look at this example shot using
the Canon 7D and stock lens that came with it, which is a pretty bad zoom lens
that goes down to f3.5, then, using the built-in light meter,
it givesme a pretty decent exposure. But if I was to shoot the same set-up using...
for example, a Nikon lens on the Canon camera, then, as you can see up here,
if I set the exposure according to the built-in light meter, then the final effect is a lot brighter
than what I got using the Canon lens. That’s actually due to the Canon digital SLRs,
it just throws off the built-in light meter if you’re not using the Canon lenses,
I’m guessing. Anyways... now to try to get that same image using Nikon lens,
I would in fact have to, according to the built-in light meter, underexpose by about...
almost two f-stops, which gives me this final result,
which looks pretty similar to the Nikon lens. So, as you can see, the built-in light meter
doesn’t always work. It doesn’t always give you the right result.
So, what I use instead is the histogram. Histograms are a great way to look at
how much light you have in a certain part of your image.
If you’re using the Red camera, you can view your scene live and have the histogram
update live for you. If you’re using Canon digital SLRs,
if you simply take a still picture of your scene, or, let’s say, a short video clip,
then play back the image and click the info button above the playback button,
then click it once more to cycle to the histogram, then you can see if you’re getting
the correct exposure. Basically, the spikes that you see there,
in kind of a wave form, it just shows you how much information you have
in that particular part of the image. If you have more spikes on the left side,
that means it’s underexposed... or not necessarily underexposed,
but that you have a lot of information in the dark areas.
A lot of pixels are really dark. And then, the more you go to the right side,
the brighter it is. So, let’s say you’re looking at this kind of standard set-up,
you’re looking for well-balanced overall exposure, meaning you don’t want anything
to be too much on the left side, or too much on the right side.
You want the information to start from the darks, then slowly grow and
have most of the information in the midtones, and then kind of drop off in the highlights,
which, if you look at this image, that is what is showing you.
Now, if you look at the red, green and blue, you’ll see, for example, in the red channel...
because just by looking at the set-up with bear eyes, I can see that
most of the colors in the scene are brownish, yellowish, which would mean that there’s going to be a lot of reds,
a lot of warm pixels in this image. And that is confirmed by the histogram.
It’s showing me that it’s properly balanced the colors because most of the information
is in the red channel, some of it in the green channel and blue, which is a color
that you don’t see much of in this set-up, it is mostly in the shadows, on the left side of the histogram.
In this set-up, the same camera angle, the same lens and so on. All we have is
this very soft, equal light, all over, both on the foreground and background objects.
Just looking at it, I know that most of the colors in this scene are brownish, yellowish,
meaning more information is going to be in the Red channel.
On top of that, there is no really any bright highlights, anything like that.
So, there shouldn’t be any spikes going off the scale, especially in the highlights,
on the right side of the histogram. And there is not a lot of shadows.
I mean, there is some shadows in the background and a little bit in the bottom left corner...
that table that you’re seeing, but most of it is pretty well balanced.
So, now let’s take look at the histogram. As you can see right away, it shows you...
sort of... the histogram confirms what you, what I would expect.
You can see all the way on the left side, there is nothing there in the shadows.
Then, slowly as we go to the midtones, it rises. There is a steady amount of information.
Then, there is that big spike there in the center of the histogram, meaning that
that neutral, middle-of-the-road grey, there is a lot of information in there.
And I know that’s true simply because looking at this figurine, it basically looks
kind of greyish, with warm colors to it. But it’s not overexposed, for example.
It is a white figure, but if I was overexposing it, then it would be pure washed-out white.
And then again, looking at the Red, Green and Blue, I can see most of the information
is in the Red channel... green a little bit less... and very little information,
only in the shadows, when it comes to the blue. Now, here is that same set-up, the same lights
and everything, but we changed the shutter speed.
So, we actually overexposed the image a bit. Again, you can see that the histogram has
a huge spike now a little bit to the right side off the center.
It just goes off the scale and, in the Red channel especially, you can see there is
no information in the shadows, and everything is out there in the highlights.
And there is these two big spikes in the highlights. That should give you a warning sign that
this image might be slightly overexposed. Now, this isn’t actually horribly overexposed.
As you can see, there is still a lot of detail in the figurine, even though it is
a white figurine... if you overexposed it, really, it should
just be blowen out... completely white, washed-out looking pixels.
But we still have some information there and so, in reality, if you had this image,
you could still take it and in postproduction, you can adjust the curves and you could
make it look how want it. Now, if I were to again look at the same set-up,
the same lights and everything, but underexposed
by... I guess, about an f-stop, then you can see again, just looking at the top histogram,
the Luma histogram, almost all of the information is in the shadows,
and then a little bit in the midtones, and then it completely drops off
and there is nothing in the highlights. So, that would send warning signs to me,
if I looked at this, and I would simply say, well...
I know the figurine is white, so I should have a lot more information in the highlights
and basically this is an image that is underexposed. Now, if we were to underexpose it even further,
then this is how the histogram would look. You can see, now everything
is in the shadows. Again, I’m just talking about the Luma histogram.
A lot of information in the spikes there in the dark areas, and then it drops off,
and nothing in the midtones, nothing in the highlights.
The same thing if you go to the reverse and you completely overexpose it
by... this is about two f-stops... no, two and a half f-stops overexposed.
You can see looking at the histogram, nothing in the shadows, which is weird,
because we know there is a lot of shadows there in the backgorund and there should be
something there on the edge of the table. And there is no information there.
A little bit of information there in the midtones, and then everything is on the right side
of the histogram. And then there is this big spike
and then it again rises up and spikes all the way on the right side of the histogram.
So, next time you are out there filming, set up your scene, camera, lights and everything
and then just take a still picture if you’re using digital SLRs,
or a short video clip. And then play it back and just look at
your histogram to see if you’re getting the right exposure.
If you’re not, make your necessary adjustments and then again,
take a still picture, take a look at the histogram, until you’re satisfied with it.
Also, I’ve been getting a lot of emails in regards to my last film “Dinner Date”.
People are asking me where they can see the finished film.
If you’ve seen some of my previous tutorials, you’ve noticed that I’ve used
a lot of examples from that film. We decided to release this film on a DVD
as a special edition with a lot of behind-the-scenes, with a lot of tutorials, talking about
how we made the whole film on a really low budget. And I wanted to know if you’re interested
in purchasing this DVD, and, if so, what kind of things you would like me to talk about.
So far, what I plan to show is... pretty much everything. Right from the beginning...
from the pre-production stage and planning, even writing the script... planning the shoot,
scouting locations, adding production value by using available locations... things like that...
to buying cheap, second-hand lighting equipment
and camera equipment... and then to the actual set-up of shots...
and then some of the little editing tricks that I used in post-production in that film.
If you guys have any specific requests, things that you would like me to talk about
in this DVD, let me know.
And also, once again, whether you have any questions, suggestions, or you are simply
interested in buying the DVD, email me at the email address that’s provided
in the description of this video.
Thank you. I hope you guys enjoyed this tutorial and before I go,
I’m going to play you a trailer of the film “Dinner Date”.
Alright. Thanks. See next time.
So how did your date with Mike go?
Meh... seriously, there is not much to say.
Mike came over... ate in a couple of minutes... then dropped his pants and was finished
before I even got my top off.
So, how did it go with Anna last night?
Amazing
Oh...
Yeah...