this video is for anyone who's ever been confused by the curves tool in affinity photo
you know that thing with the strange graph and the diagonal line through it
the curves adjustment is one of those tools that just doesn't make any sense at first glance
and most videos you watch don't explain how it works either they just tell you to
move the curve up to make the image lighter or down to make it darker so in this video
i'm going to explain exactly what's happening when you make a curved adjustment in affinity photo
because once you understand how it really works you can use the curves to make precise changes to
colour and light in your photos i'll be showing you a bunch of things that are often overlooked
when making a curved adjustment we'll start by adding a new curves adjustment layer to this image
you can do this by clicking the adjustment icon at the bottom of the layer studio panel
then in the list of adjustment layers click the curves option this is the curves dialog
where you can see the diagonal adjustment line and the image histogram behind it the histogram
is to help us when we're adjusting the image but i need to show you something that's often overlooked
if you compare it to the affinity photo histogram panel at the top you'll see that it's the same
now watch what happens if i make an adjustment only the histogram in the histogram panel actually
changes the adjustment doesn't do anything to the histogram in the curves dialog that's because the
histogram in the curve dialog reflects the image layers below it in the layers panel the histogram
at the top of the screen is for the entire image including the changes i made to the curve
let's reset the curves layer now by clicking the reset button at the top another feature
that's often overlooked is this picker button to add a new point to the curves line click on the
button to activate it and then click on a tone in the image that you want to adjust then whilst
continuing to hold down the mouse button drag up with the mouse this adds a point to the curve
determined by the brightness of the pixels where i clicked on the image it's a great way to select a
tone on the curve to adjust if you don't know where it sits on the curve's adjustment line
the other way to add a point to the curved line is to click it with your mouse now watch the x and y
boxes at the bottom of the dialog when i click and drag one of the points on the curves line their
values change when you understand what these are it will help you understand the curve's adjustment
the grid you see in the curves dialog is really a graph with an x and y axes the x-axis along
the bottom of the grid represents a range of brightness on the left side we have a value of
zero representing black then on the right we have a maximum value of one representing white between
these two extremes we have values representing different shades of grey the darker values are
on the left and as we move to the right the tones become progressively lighter if we pick a point
in the middle of the graph it represents the midtone gray with a value of 0.5 this brightness
range along the bottom of the grid represents the brightness of the pixels we're adjusting in
the image in other words the ones below the curves layer in the layers panel and which are shown in
this histogram now watch what happens when i move the midpoint up to lighten the image the x value
remains around 0.5 depending on how steady my hand is but the y value has increased to around 0.6
the y-value represents the brightness level in the image this is what the histogram in the histogram
panel at the top shows us and just like with the x-axis the y-axis runs from zero at the bottom
representing black to one at the top representing white i'm sure you noticed when i made the change
to the midpoint it didn't only affect the midtones in the image that's because the curved line
moved to a higher value on the y-axis along its entire length the only exceptions are the points
at either end if you look at a dark gray tone with a value of 0.25 on the x-axis it's increased
to around 0.32 making those pixels lighter the same is true at every point along the curves line
except for the two end points this is why it made every pixel in the image lighter now look at the
original histogram in the curves dialog and it doesn't extend either to the black or white end
this means the darkest pixel in the image is dark gray at around 0.1 and the lightest
is light gray with a value of about 0.95 it's also why this image appears washed out
let's look at how to fix it using the points at either end of the curves line
click and drag the black point of the curve on the right until it meets the edge of the histogram
this turns the darkest pixels in the image from grey to black
those pixels previously had a value of 0.1 but the new value on the y-axis is 0 or black we can then
do the same with the curves white point moving it left check the main histogram panel and the
histogram now extends from left to right because we fixed the contrast look at the difference
when i turn the curves layer off and on let's now look at the drop down channels list in the dialog
all the changes we've been making have been made to what's called the master channel
when we change the master channel it's like making an identical change to each of the color channels
in the image by making the same adjustment to all color channels in the same level we don't affect
the colors in the image but watch what happens if we change the drop down to the red color channel
now when i click the curve and move it up i increase the level of red in the image and
when i move it down it removes red from the image it's possible to adjust the curves of individual
colour channels to colour correct an image let me show you one way to colour correct this image and
fix the contrast at the same time i'll just reset the curves adjustment before we start
i'm starting by picking the red color channel in the drop down list
notice the histogram then changes to display only the histogram of the red channel i can then move
the black point and white points of the curves line to meet each end of the histogram it's a
good idea when doing this to also change the main histogram panel to display the red channel as well
you can use it to help you judge when the histogram extends to each end without
clipping now i can change to the green channel and do the same thing don't worry that it makes
the colors in the image look odd because we'll fix that when we've adjusted all three channels
finally let's change the blue channel
you can now see the colors in the image have been corrected and it's fixed the contrast at the same
time then if we change back to the master channel we can use that to adjust the image brightness
now for another secret that's often overlooked the reason we had a red green and blue channel in
the channel's drop down isn't because this is an rgb image it's because of this other drop down to
the left here you can pick the color channels that you want to adjust and work with like cmyk and lab
just remember that changing to a different mode resets any adjustments that you've made previously
as you can see there's a lot more to the curved dialogue than you might initially think
but it's also not as difficult to understand as it first appears
if you've learned something new in this video you may want to watch this one next
it explains three things that most affinity photo users don't know but which may just
help you i hope you've enjoyed today's video and if you haven't already don't forget to subscribe
thanks for watching i'm robin whalley and i hope to see you soon for another video