In this episode we'll look at how the RGB histogram can help you solve exposure problems.
AdoramaTV presents 'Exploring Photography' with Mark Wallace.
Hi everybody, welcome to this episode of 'Exploring Photography' right here on
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Well, I'm out here on this beautiful balcony just outside of my rental apartment in Paris, France
and these roses just bloomed a couple of days ago and I thought I would
take some pictures to send back to family and when I took a picture
well guess what? This rose showed up as a big red blob, so what's going on?
Well the answer has to do with something called color channels. Now, as we all know way
back in elementary school we have what's called primary colors: red blue and
yellow, and you mix those in paint to get all the other colors.
Well in light we have primary colors but it's red, blue and green: RBG.
And you've probably seen it all over the place has sRGB, RGB color spaces, things
like that. That stands for red, blue and green and when we take a picture
those colors are recorded in what are called color channels so the red, blue
and green color channels. So what was happening is when I took this photo one
of those color channels had some problems so let's walk through that.
So what I've done here is, I have my camera set to fully in aperture priority mode and I'm
gonna go in here and shoot exactly as my camera is telling me to shoot so I've
got my rose here and this is giving me a shutter speed of about a twenty-fourth of
a second and we can look at that and see that it is just that red blob that I was
talking about. Now when I go into the back of the camera and I'll show you my
histogram here. Well, it looks like everything is just fine but the problem is my
normal histogram is lying to me. What I need to do is see all of my different
color channels on a histogram to see what the problem is so what I'm going to do here
is I'm gonna go into my camera's menu
and then I'm going to go into where the histogram is and make sure I
have this set to RGB histogram and once I do that, changing it from the standard
histogram to the RGB histogram, and I look at that same picture... Wow, now I can
see that my red channel is clipped. It's way to the right side of that
histogram and its overexposed. That's why this is a red blob because all the
details are just over exposed. So what I need to do is use exposure compensation
to bring that red channel back into proper exposure.
Now that looks to me... I'm just going to guess this by experience, that that's about a
stop and a half overexposed. So now I'm going to go into manual mode. I'm going to override
what my camera says to do and what I'll do here is that once again, I'm going to
look at my meter and then I'm going to underexpose by about a stop and a half
and make sure I'm all in focus here and now we'll take that picture again. Now I'm in
a 60th of a second and now look at that. Now our red rose shows up as a red
rose and when we look at our histogram on the back of the camera and you can
see that that red channel has shifted to where the highlights are which is where
it should be and that's what you need to do if you're getting those red blobs in
your flower pictures or other environmental shots if the red channel
is out of whack, well you just need to underexpose a little bit and the only way
that you're going to know they need to under expose or technically you're
exposing correctly is if you have your RGB histogram turned on. You can't always
trust that standard Luminosity histogram and once you do that there's
some other things that you might want to do and so to explore that a little bit
further we're going to hop into Lightroom.
Now that we're in Lightroom let me show
you a couple of things. The first one here is that horrible picture that we took using
the built-in meter of our camera and we can see clearly on the histogram in
Lightroom that it
agrees with the camera and that the red channel is way out of whack
Now the second photo that I took, this is the one that i shot at a 60th of a
second you can see now that these reds, this red channel, they're coming right to the
highlight area just to the right of the mid tones. Now after I got done filming I shot
one more exposure at a 90th of a second and then placed my red channel
right here in the mid tones and I think that's the image that I like best and
that's a really good thing to do is if you're shooting something like this
where you've got one of your color channels it's out of whack, shoot
several exposures see you have something to work with.
Now the other thing I wanted to show you and I think this is the most valuable
tool for working with color and that is the color checker passport made by X-Rite.
Now what I did was I took my color checker passport and I just quickly took
a picture of that next to the rose and then what I can do is bring that photo
into Lightroom and use it as a tool for working with my color. Now, we don't have enough time
to go into all the things that the color checker passport can do but i want to show
you a couple of them that are really powerful really quickly. If I zip over to the
develop module and I've zoomed in here on my color checker, notice that we have
two rows of squares on this top panel here. These are for setting white balance,
and notice that the top row has a little person and the second row has a
little mountain and sun.
Well, the top row is for working with portraits and the second row is for
working with scenic photos and what you can do is you can get your white balance
picker and you can choose the square with the notch out of it and that is
going to give you a neutral white balance. If you want to warm up the scene
slightly you click on one of the squares with the plus. If you want to cool it off you
click on the squares with the minus. Now these work a little bit differently. The
portrait squares will warm up the scene so it's pleasing to skin tones and the
scenic photo squares will warm up or cool off the scene where it's pleasing to
greens and reds and flowers and things like that, so that's why there's two
different colors.
So we have set, really quickly, a neutral white balance that's highly
accurate and the other thing that I really like to work with is the ability
to use these top colors here to work with the colors inside of my photo and
notice we have red and orange and yellow and green and aqua etcetera, and they
match exactly with the colors over here on our HSL sliders, which means we can go
in if you want to work with let's say luminance to take the luminance of this
red flower down a little bit. I'll click on my little dot here and that gives me a tool
where I can click on the red square in my color checker and notice I'm only
affecting the red in this image so I can bring that down just slightly, and I want
to change the saturation and click on saturation and I've got my little square
again. I can boost or take my saturation down just using my little square. The other thing
that's nice is if you're adjusting a lot of things in your hue saturation and
luminance sliders you can see what they're doing to the overall image just
by looking at your color chart here. It's really nice we don't have a lot of time
to go into that, actually don't have any time to go into that, cause I want to
show you one more feature that i think is the most powerful feature of this
tool and that's its ability to let you create color profiles. Now, if we go to the
very bottom of our develop module down to camera calibration, notice there's this
thing that says profile. And by default it will say embedded or Adobe standard or it
might match what you shot on your camera, vivid or scenic or something like that.
Now, watch what happens if I change this from embedded to Adobe standard. My colors
change slightly. There's a shift in the reds and the blues. Now, this might not show up
because of the compression that YouTube puts on the videos, so switching
between these on my computer screen I can see a big shift in the colors but
that might not show up in the video so I highly recommend you take a photo of
something that's really colorful that has reds and greens and blues and
yellows, and do this yourself. Click between your different color profiles to
see how the colors are shifting and you might be surprised. What we want is
highly accurate color
and so the x-rite color checker passport allows us to create our very own profile
All you have to do is go up to 'File', 'Export with Preset', 'Colorchecker Passport'.
It's going to ask you for a name and I'm going to say red rose and save. It's going to
evaluate this bottom portion of our passport to make sure our colors are
absolutely accurate. Now you have to close and restart Lightroom once this is
finished, it takes a couple of minutes and so with the power of video editing
we're going to jump right to the finished product.
OK, now that has finished and we can go down again to the bottom of our
camera calibration. Over here it says Adobe Standard. Now, look, a red rose shows up. If I click
that, now I have my calibrated color profile that's specific to my camera and
lens. It's highly accurate, and then we can go in and do all the things that we need to
do to make sure that this is absolutely the perfect color and then we can
use some other X-Rite tools to profile our printer in our screen and what we
see is going to be exactly what we print. That is a topic for a future episode.
Well, that's how color channels affect your exposure, so if you're getting red
blobs or other issues in your photographs, turn on your RGB histogram
so you have a full understanding of what your camera's capturing by color channel. You
might be surprised what you learn.
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also check out the Adorama Learning Center. There are tons of articles and
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of stuff, so check that out it's absolutely free as well. Thanks again for
joining me and I will see you again next time.
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