hello I'm Robin Whalley welcome to Lenscraft in this video I'm going to be
explaining the curves adjustment because it's one of the most confusing but the
most powerful and easy to use adjustments once you understand a few
things in a previous video I looked at the levels adjustments but if you
haven't already seen this I really recommend you watch it I'll put the
details in the video information below one of the things that we looked at in
the previous video was this image and it tries to explain image tones because
this is very important when it comes to understanding how the curves work what
it shows here is two different representations that you might find in
different software basically down at this end of the strip
we've got pure black and over at this end we go to pure white how those tones
are represented in software tends to be using one of two approaches the first
one is the tonal values here from zero running up to 255 with one to eight
being a mid-tone gray the other scheme tends to use percentages which runs from
zero percent up to a hundred percent and effectively is the amount of brightness
that you have in the image so a zero percent brightness it would be black
where is at 100% brightness you'd have white and at 50 percent brightness again
you've got mid-tone gray now this is all very important for understanding levels
but he also improves our understanding of the curse tool so let's go and have a
look at the curves adjustment now I've already added a curves
adjustment over here to my image and I'll just display the properties window
and that shows you the curve that you're probably used to seeing now a lot of
people simply go about adding points on to the curve and adjusting it like so
and there is some understanding of how it works but not a great deal in this
video I want to explain to you exactly what's happening on the curves tool how
to read it and how to understand how it really works so the first thing you need
to understand is that there's two axes for this the horizontal axis is all
about what we call the input values so these are the tones that you see in the
image now and over on the left side we've got pure black and over on the
right side we've actually got pure white and you
can see that represented by the balance here running from black through to white
just as we had on the gradient previously that I showed now cuz I say
these are the input values so the tones that you see in this image if I click on
this point adjuster here as I move my cursor over a point in the image you can
see that the tonal value is being shown on this curved line here so if I move to
a darker point you can see it's further to the left if I move to a bright white
point it's over on the right of the curve now the curve at the moment is a
straight line and the reason for that is this other access this y-axis here that
we've got runs vertically again that shows from black through to white and
what it represents is the changed value of a tone in the image once you've
adjusted it let me show you how that's going to work so I'm going to click on
the central point in the curve and you'll see down here that that has an
input value of 1 to 8 remember what I said that's mid-tone gray we also have
an output value that's identical 1 to 8 if we read this we can see that the
central point between 0 and 255 is one to eight the output value is also
one to eight so what this is saying is at the moment the curves having no
effect so a mid-tone gray value of one to eight it's being translated into an
output value of one to eight as well so there's no change if I move that up by
one square you'll notice that my input values one to eight but my output value
is no one five four so the mid-tone grays in this image are
now being turned into something that's lighter and as a result the overall
image looks lighter you can see that if I turn the curves effect on and off now
one thing I should mention is that you've probably seen lots of little
squares on my curve background here and you're probably looking at a curves
adjustment that has only four squares if you hold down your old key or your
option key and then click on the grid you can toggle it between having four
squares and having ten squares I prefer the ten squares because I think it gives
me a better understanding of how far I've moved something so let's go back to
reading this grid a little bit further we've already said the input value of
1/2 80s where I've added point we've gone to one five four with it for the
output value makes everything lighter and the reason it makes everything
lighter is because if you look along the curve now every point is above the
original diagonal line so every tone in the image becomes brighter in some way
now as we get nearer to the black point the increase in value from where the
line was previously and the new line is smaller so the curve adjustment that
we've added has less effect on the darker tones and the further away we get
from the center point the less the effect is until we get to black where
we're having no effect at all the same is true at the other end where we go to
white now we can also take this level adjustment that you see here and we can
move it to the left and that will actually move the tones the brightest
homes in the image took white and the game as before if you
hold down your Alt key or your option key as you move this you can see the
areas of the image that start to clip so we can introduce some very limited
clipping if we want to now notice up here the point that's being added at the
moment this shows an input value of 2 for 2 so something that wasn't quite
pure white before now becomes in the output value 255 pure white and you can
do the same with black now if I move that into the towards the center hold
down my Alt key I can see where the clipping starts in the shadows again
what I've got here is an input value of 6 or something that wasn't quite pure
black now as an output value of 0 or pure black you can't move it the other
way and actually grab that point and move it up and when you do that you take
the black out of the image so a value of 0 or something that should be black
actually becomes 26 something that isn't black at all it's just dark gray now
let's look what happens if you move something below the line so here we've
got point of 77 as the input and that now has a new value of 100 we can drag
that back down to our original output value now I'm finding it difficult to
actually make the to match so one thing you can do if you want to work precisely
is say 77 + 77 so you can actually enter the values in the input and output
fields now look what that's done to the curve them whilst it house move the
curve the original curve but down to its starting point it's actually moved the
curve as well down here to darker values so if you want to stop that from
happening you've got to add another curve point and move that back up again
just to maintain the straight part of the line here it's also added a lot of
contrast into the image and when you add contrast into the image by working on
the RG channel his ends up saturating the image
so look out a saturation as increased here as a result of adjusting the curve
now all those adjustments are too strong but the idea here is that you understand
what the curves tool is doing and how to read it and it's all about these input
and output values again and understanding that this horizontal axis
represents the input value whilst this vertical axis represents the output
value once you understand that you understand how to use the curves tool
now let's have a quick look in a couple of other applications also have curves
this time I've got the image open in affinity photo and we can see over here
in the studio panels on the right we have a curves adjustment and I can add a
new curves adjustment just by clicking the option here the tools on this are
slightly different from the Photoshop version I showed you earlier but the
underlying principle of how this works is exactly the same you can pick the
channel that you want to adjust in this case the master Channel or you can pick
the individual red-green-blue channels or an alpha Channel when we pick the
master Channel all we're doing is we're adjusting all three of the channels the
color channels red green and blue to the same level and that is what maintains
the colors in the image if I adjusted one of the channels in
isolation it would change the color balance of the image again we have a
horizontal axis and we can put a point on that and move it up now what we can't
see is the input and output values for the image but the overall adjustment
remains the same you've got this input value mid told moving up to a lighter
value here and again we can pick the curve at either end and we can move that
in to adjust the brightest homes so these the principles of the curves tool
and the adjustment remains the same even though this is a simpler version
and a Photoshop one let's take a look in another adjustment
tool here we are this time in capture one and I've taken the curve from the
site panel and just pulled it out so you can see what we're doing now this is a
simpler curve than the others but it still has all this power so again I can
adjust the RGB Channel which is the red green and blue channels or I can pick
the luminosity Channel the red Channel green Channel or blue Channel again I
have an input and an output value and they also have a picker tool which
allows me to pick and add a point based on any point in the image you don't have
to use the picker tool though you can actually just use and click the point on
the curve that you want to adjust so again I can up my mid told input value
of one to eight and I can move that up to lighten the curve and here we can see
the input value for the point that I've got selected down here and the output
which is on the vertical scale so again the curve is working just the same even
though it's slightly different in capture one and it's the same across all
the different tools that you use the curve works in the same way so once you
understand how to use it in one you can apply that knowledge to the other
editing tools allowing you to quickly understand and improve your images I
hope you found this useful I will be publishing future videos covering other
common tools if you've got any suggestions about good tools to cover
please let me know in the comments below it would be really helpful I'm Robin
Whalley you've been watching lenscraft I'll see you soon for another video