How to Use the Curves Tool in GIMP

hello and welcome to yet another tutorial by Davies media design my name is Michael Davies and in today's tutorial I'll be showing you an in-depth look at the curves tool i'll be using 2.10 point 18 which is the latest version of at the time of this tutorial but of course before I get into that I want to direct you guys over to my website at Davies media design com as always I have tons of and Inkscape tutorials on here as well as my book of layers and and Inkscape help articles so definitely check that out you can enroll in my 2.10 masterclass from beginner to pro photo editing on udemy you can enroll in any of my scholarship classes by visiting school calm and he can get more with a premium membership to Davies media design more premium membership includes access to my Help Center app as well as ebooks like my book of layers and exclusive content not found on YouTube you can start your premium membership with a 7 day free trial and I'll include a link to this as well as all the relevant links from this tutorial in the description of the video so the curves tool is a sophisticated tool for adjusting the brightness contrast and colors in your image you can also adjust the alpha channel in your image if your image has an alpha Channel there are more simplified tools in that performs some of the same things that the curves tool performs including the brightness contrast tool or the color correction tool the levels tool is also similar to the curves tool it is also a sophisticated tool for brightness contrast and color correction although the curves tool is going to be a bit more complicated and it's also going to provide some more flexibility in terms of adjusting the value of your pixels and the colors of your pixels I do have an entire tutorial dedicated to the levels tool if you want to check that out and I do want to point out even though the curves tool is going to be a bit more complicated than something like the levels tool or the brightness contrast tool I am going to break it down today in a way that beginners can understand so here is the color curves dialog it says adjust color curves the top part is the presets which I'll get into a little later on in this tutorial but below that we have channel and this allows you to select whether you are adjusting the value red green blue or alpha channel my image right now does not have an alpha Channel so that option is grayed out at the moment so we're going to start by working on the value Channel and over here you have four icons so the far left icon is going to allow you to adjust curves in linear light the right icon allows you to adjust curves perceptually I'm going to recommend sticking with perceptually as that's what your eye is going to see and this mode is what a lot of the more popular file types use such as a JPEG and then to the right of that you have the linear histogram option or the logarithmic histogram option if you have something like an image you're going to want to stick with the linear histogram option as this is going to do a better job of displaying all of the values and colors in your image when you have a more complicated value in color set on the other hand the logarithmic option is going to be better whenever you have an image that contains mostly a single color so for example your image is mostly red so the reason for this is that under the linear histogram option you're just going to have essentially a single bar going to the very top on a single pixel here or just a couple of pixels whereas the logarithmic histogram is going to spread that out as you can see it's a bit more evenly distributed here when we have logarithmic selected but for something like an image we're going to stick with the linear histogram so you have a grid here and you'll see that as I move my mouse pointer around you could see the exact coordinates that our mouse is located on this grid more on that in a second but the line going across the diagonal line is called the linear curve of course this is a straight line right now but as we add what's called notes to this it'll turn this into a curve we're going to get into that so behind the linear curve and the graph you'll see a series of bars here and this is known as the histogram the histogram is going to show you a distribution of the pixels in your image so in this case because we're on the value Channel it's going to show a distribution of the brightness or the darkness of our pixels so on the left side here is going to be our shadows and if we have tall bars here these bars represent pixel values if these bars are tall in a specific area that means we have more instances of those pixels in our image in that area so in this case it's telling us we have more instances of darker pixels which you could see based on things like the shirt here which is dark and just dark areas here within the picture so the left side is going to be the shadows the center is going to be the mid-tones as you can see not a whole lot of mid-tones going on in this particular image and the right side is going to be the highlights and there's a big gap here between where the histogram ends in the far right side of our histogram that just means there aren't a whole lot of really bright pixels such as white pixels there aren't really any blown-out pixels here so if we had a very bright white sky we would probably have more of a right skewed histogram with some tall bars going on the right side here instead our histogram is skewed to the left that means we have a slightly darker image so below the histogram is going to be the input range this is the gradient that you see here going from black on the left to white this input range by my definition is essentially just going to represent the values that you see here in the histogram these are the original values of your image so again the left side is the shadows the right side is the highlights in the middle are the mid-tones so that's just what this is representing the output range is going to be the left gradient here that's going to go up and down the up portion is going to be white down is black so this is going to represent the new values that we're going to be creating by moving the curve here making adjustments to the curve so anytime we move the curve upwards is going to make the pixels in that area brighter and anytime we move it downwards it'll make those pixels darker we'll get into what these settings are here in a moment but now I'll demonstrate adjusting the curve using the input range which is the original values in the output range which is the new values and we're going to adjust this curve using our mouse based on what are called nodes so we can add a node to our linear curve using two methods if I simply click anywhere on our grid and you can see the exact location I'm clicking on using these coordinates that is going to cause the curve to just snap to that coordinate that I clicked on and you can see that area where it snapped here is going to be a node so the node is this little dot you can see here and let me just expand this to make the curve a little bit larger so that's one way of creating a node I'll reset this I can also use a modifier key so if I hold the control key and I click anywhere on my linear curve that'll create a node there on the linear curve without moving the actual histogram and of course I can after the fact move this around so I could drag it up to make everything brighter drag it down that makes everything darker so let me reset so let me come back over here and just click and drag this up like I had done before so there we have our node and our linear curve is now curved upwards here it's now bent upwards and you can see our original linear curve line here it's a faint blue line at the moment hopefully you guys can see that on the video that was the original location so whatever that line is still there that means that the curve has been unchanged and therefore all the pixels and the image are unchanged but in this case because we clicked and dragged the curve upward the curve is no longer unchanged and what you have here is that all the pixels that are within this area here within this range we've created are now going to become brighter pixels so that's why when I clicked and dragged near this area the left portion of my histogram a lot of my darker pixels for example became much brighter and that's because there is a lot of separation here between the original linear curve and the new curve so the greater the amount of separation the brighter that's going to be when we're dragging it upwards so let me just drag this note I can drag it to a new position here so you'll see the darker parts of my image will get even brighter now and even some of the brighter portions of my image because there is some separation here between the original linear curve and the new one are going to also get brighter on the other hand if I drag it in the opposite direction that's going to make the pixels darker so everything in this area is going to represent a darkening of those original pixels the further away line is for that particular area that contains those pixels the darker those pixels are going to be so these pixels over here won't be quite as dark the pixels right here that have the most separation will be much darker so hit reset some of you might be asking well what if I don't want all of my pixels to be affected when I'm adjusting the curve the solution to that is going to be to create an anchor node so an acre node is essentially just going to lock down any area that you don't want affected so for example I'll hit the ctrl key and click in the middle here that is going to create an anchor node near the middle of my histogram of my curve and then if I come over here and let's say I just click to have the curve snap to this new location you'll see what happens is that only the areas to the left of my anchor node are going to be affected so in this case only the darker pixels in my image become brighter that in my opinion right now does not look great so I'm actually going to tone that down quite a bit so I can come over here and preview before and after so it's a bit brighter now so you guys might be asking if these bars here are so tall why are we increasing this value even more the answer is that the tall bars in the histogram just represent a lot of instances of that type of pixel in the image in this case we have a lot of instances of darker pixels so we want to brighten those darker pixels not make them even darker on the other hand over here we don't have a whole lot of light pixels going on and actually what I can do to fix this gap is similar to what you can do with the levels tool so with the levels tool you have the shadows and the highlights slider and usually you bring those sliders in and that's going to allow you to basically change the black point or the white point so we're going to do the same thing here and if we wanted to change the white point of this image which is going to be the point at which the brightest pixels become white we can click and drag this top node here and we can just drag it to the left and you'll see that as I do that the image is going to become brighter the issue with this of course is that the overall value of the image doesn't look right when we drag it too far over so we're not going to overdo this and I'll just leave it right there you can do the same with the black point so I can always move this black point inwards and that is going to change the black point of my image so we can also make adjustments here by clicking on the curve and we can drag it up or down if I drag it up it's going to make our bright pixels brighter if I drag it down it'll make them darker so there's a before there is an after so I'm just going to leave these Corrections where they are for now but I do want to explain real quick before we go over to the color channels down here we have input and output this is showing you the exact location of whatever node you're clicked on so if I click on the middle node you'll see that's close to 50/50 if I click on this lower left node you'll see the input is thirteen point five two and the output is eighteen point seven eight so the input was the original number and the output was the new number we created by adjusting the curve so the new value of the pixel if the output is greater than the input that means the pixel is now going to become brighter on the other hand if the input is greater than the output that means it's going to become a darker pixel so if I come over here the original output was one point seven nine the new output is going to be zero which means that this is now going to be a darker set of pixels additionally we have type and if I click on a node you'll see right now the default type is set to smooth I can change that's a corner and what that'll do is it'll change the curves that are going through this node into straight lines and we can make every single curve a straight line by clicking on each individual node and just changing that to the corner option including these nodes here and now everything is a straight line I'm just going to switch this back to a curve finally below that we have curve type and right now this is set to smooth if you wanted to you could freehand the curve so I'm not going to select that right now but if you did have freehand selected I could sit here and hand draw with my mouse a curve and that would be reflected over here in the final image of course we have the split view options so that's going to give us the option to see it before and after and just move the split view line here and that way we can compare our results so that's the value channel which again represents brightness but I can also adjust the colors in my image using the curves tool so what I'll do is I'll come over here and change the channel to red the red channel is going to be essentially the same as the value Channel except instead of adding brightness or taking it away we're going to be adding red saturation if we drag the curve upward or we're going to be adding the cyan saturation if we drag it downward cyan is opposite red on the color wheel so over here the output range instead of it being a white to black gradient that's going to be a red to black gradient and that's representing adding red saturation or removing it in my opinion this should be a red to cyan gradient but that's okay we still have the input range down here which is going from the darker pixels on the left to the brighter pixels so essentially we're either adding red or cyan saturation to a pixel value on our image so this is showing us that we have more red going on in the darker pixels in our image and there's again a huge gap here so really no red in the highlights of the image and it's skewed to the left so once again I'm going to ctrl click to create an anchor node you can see the exact location there and then since we have a lot of red going on in the shadows of the image I'm going to click and drag this down and you'll see that as I do that that's adding cyan if I go way down it's going to add a ton of cyan and actually let me reset the channel and show you this is what happens when we don't have an anchor node there so it's all red or it's all sy and I'll hit reset again control click to add that anchor node and let's come over here and adjust this so I'm adding more cyan to the darker portions of the image and if you want you can come over here and we don't have a whole lot of red going on so we could add a little red to the highlights I of course don't want to over do that so we'll leave it there for now and we'll switch over to the green channel so this will be the same thing as the red Channel the difference being that you're adding green saturation or you're adding magenta saturation so you'll see over here the output range is now green to black again the histogram is skewed and we have a lot of green going on in the darker pixels that's probably because of the background here so I'll control click let's add an anchor right about there and now I can click to add an anchor and I can either add more green to the shadows of the image or I can add more magenta I'm just going to add a little bit of magenta for now and then we can test out and see how this looks when we add some green to the highlights or magenta and actually I'm gonna reset the channel here I don't like the way this looks with the anchor so you can always just do away with the anchor click and drag and I think this might actually look better with just a single note here that way everything is getting a bit of magenta added but it's decreasing the amount of magenta added as we get closer to the highlights so here's before here is an after I'll leave that there for now and I'll come over to the blue channel so with blue you're either adding blue saturation or you're adding yellow saturation and you can see here here's the yellow saturation here's the blue saturation I'll hit the reset channel button so in this case we have a decent amount of blue going on and you can see we're skewed to the left with a lot of blue in the shadows of the image and I'm just gonna click and create a single node and you can see that as I drag this downward it's adding yellow mostly to the shadows it is adding some to the highlights as well so here's a split preview before on the right after on the left so you can see the colors look a lot better and the brightness looks a lot better as well in this image if you wanted to you could always come back to the value Channel or any of the channels and make further adjustments you might change your mind as to how you want the image to look after you've added some color and if we dragged just the middle here it's going to brighten or darken the mid-tones so next you'll remember in the beginning of the tutorial I mentioned there is a presets option so if you wanted to save the settings you just performed on this curves tool for a future image you can come over to the presets row here and just click the little plus icon so that's going to allow you to create a new preset with whatever name you want so maybe we name this outdoor portrait that way it's descriptive of what this preset works with and I'll click OK now when I click the presets drop down if I'm doing this on a future image you'll see the outdoor portrait preset is now saved in here so we can use that later once we've made all the changes we want I'll click OK so there is the image edited just with the curves tool of course usually you're going to combine the curves tool with things like the saturation tool the shadows/highlights tool the levels tool the vignette tool etc so this is a pretty powerful tool on its own I also want to show you some commonly used shapes with the curves tool so come back here to colors curves so the most commonly used shape that I use often in my tutorials is the s-curve this is going to add contrast to your image so to create an s-curve all you do is click near the highlights and drag that upwards and then you come down here to the shadows and you're going to click to create a node and drag that downwards so you're making your highlights brighter and your shadows darker and then if it's too much contrast you can always bring in these nodes in the lower corners upwards and that's going to flatten the image out a tiny bit so there we have an s-curve and that as you can see is adding a lot more contrast maybe a little too much contrast and one thing I want to know is that if you add a node here and let's say you make some adjustments and then you realize you don't really like that node here you can always just click on that node and drag it off and now that node has been deleted so once I finish my changes I'll click OK to apply them and I'll come back here to colors curves so another curve type is the inverted s-curve that's just going to do the opposite so it'll make the highlights darker and the shadows brighter so you could see that is the final result of that and I'm just going to hit reset by the way the reset button will reset all of the channels including the value and all the color channels it won't just reset the channel you're on in this case it's ok because I haven't really done anything on the other channels it can always just hit reset channel if you don't want to undo all of your work on the other channels another shape is the inverted curve so if I invert both of these nodes here you'll see that's just going to basically do the same thing as if I went to colours invert so it's just inverting all the colors in my image all the values of my image and obviously I don't want to do that so I can reset that also you saw earlier if we just bow the curve outward that'll just brighten the image overall for the most part especially if we start in the middle of the Irv and if we bow it downwards that's going to darken it overall so I cancel alright so that's it for this tutorial hopefully you liked it if you did you could check out my youtube channel at youtube.com slash Davey's media design don't forget to click the bell icon to be notified each time I have a brand new tutorial you can also check out any of the links to my resources in the description of the video but thanks for watching and I'll see you next time

Channel: Davies Media Design

Views: 32,251

Rating: 4.9380531 out of 5

Keywords: gimp, gimp tutorial, gimp for beginners, how to gimp, GIMP 2.10, GIMP, basics, curves tool, GIMP 2020, GIMP 2.10.18, photo editing, photography, brightness contrast, color correction, photo editing for beginners, linear, logorithmic, tone curve

Id: CmNAmwRZjGU

Length: 20min 21sec (1221 seconds)

Published: Wed Mar 04 2020