How To Draw Curves In Gimp

The curves tool is a sophisticated way to adjust the brightness and contrast of your image, besides every bit color correct your image. It is similar to the levels tool in the blazon of adjustments information technology makes to your image, likewise equally the fact that both tools utilise a histogram to display pixel values. Nonetheless, the curves tool uses a curve to adjust your brightness and dissimilarity and the three color channels of your image rather than using shadows, mid-tones, and highlights sliders. This provides more flexibility than the levels tool, but also increases the amount of complexity in the tool. So, the curves tool is not quite every bit beginner friendly.

With this tutorial, my hope is to make the highly useful curves tool more accessible for beginners. If y'all adopt to watch a video version of this tutorial (in English language), you tin practise so beneath. Otherwise, you can read the article below, which is available in a diverseness of languages. Let's begin!

Introduction to the Curves Tool: The Layout

For starters, the tool tin be accessed by going to Colors>Curves (blood-red arrow in the epitome above).

At the top of the Curves dialogue y'all'll see a dropdown titled "Presets" (reddish arrow in the photo above). I'll get into this later.

Below the Presets department is some other department titled "Channel" (blue pointer in the photograph above). This allows you to select the channel you lot'd similar to edit for your prototype; the options are Value, Red, Light-green, Bluish, and Alpha. The Value aqueduct represents the effulgence of the paradigm. When you make edits to this channel with the curves tool, y'all will either make your pixels brighter or darker.

The Red, Green, and Blue channels are all color channels. When you lot make edits to these channels using the curves tool, you lot are either adding saturation for that color (i.e. for the red channel, you are adding saturation to the reds in your image), or you are adding saturation to the reverse color on the color wheel (for the opposite of scarlet, you add Cyan).

The Alpha channel represents your image's transparency. If your paradigm does non currently have an alpha aqueduct, this option will be grayed out (as you can come across in the epitome to a higher place). This concept is a scrap more than complicated, and so I'll save it for later on in the tutorial.

The main area of the Curves tool below the Aqueduct section is where you'll be making your edits. Hither, y'all'll see a grid with a diagonal line going through the middle of it. This line is called a linear bend (red pointer in the image above). Information technology is straight for now, but it will become a curve equally we add together nodes to it and change the position of those nodes.

Behind the grid and the linear bend is your image's histogram (blue arrow). The histogram displays the values of the pixels in your image like a bar graph.

The far left of the histogram represents the darkest pixels (shadows – highlighted in blue in the paradigm above), while the far correct of the histogram represents the brightest pixels in your prototype (highlights – highlighted in green in the image above). The center portion of the histogram is the mid-tones (highlighted in red in the image). The taller the bar for a single value in your histogram, the more than instances in that location are of that shade or color pixel in your paradigm.

In this instance, the histogram is skewed to the left (highlighted past green in the above photo), which means our image is a bit on the darker side. Additionally, in that location is a cluster of pixel values towards the left side of the graph that have tall bars (ruby-red arrow). This tells me in that location are a decent amount of pixels that have this particular shade, which is a darker shade.

If I had an image with a lot of vivid pixels (i.e. a diddled-out sky), the histogram would exist skewed to the right and would have several alpine bars representing high instances of bright pixel values on that right side of the histogram.

You lot'll also detect that at that place are two gradients – one horizontal gradient along with bottom of the graph and 1 vertical gradient on the far-left side of the graph.

The gradient forth the bottom of the graph is chosen the Input range (crimson pointer in the above photograph). The gradient goes from black on the left side (green arrow) to white on the right side (blue arrow). As I touched on earlier, this represents the current pixel values of your image – with the darkest values on the left side of the histogram and the brightest pixels on the right side of the histogram. So, in other words, the bar values I talked most stand for to the gradient at the bottom of the graph. The higher the bar at that detail point in the Input range, the more than instances at that place are of pixels in your epitome with that exact value.

If you lot have a really alpine bar at the far-left cease of the histogram, that means you have a lot of black in your epitome. If you take a really alpine bar at the far-correct of the image, it means you have a lot of white in your image. If you lot take a really tall bar in the middle of the histogram, information technology means y'all have a lot of mid-tones. (these statements are more true when you lot have clusters of "alpine bars" in an area of your epitome – non just a single tall bar)

On the other paw, the gradient on the left-hand side of the grid is called the Output range (red arrow in the image above). This represents the new values you want to set your pixels to. The gradient is black on the bottom (blueish arrow), and white on the meridian (green arrow). All this ways is that dragging your curve upward will brighten existing pixels, and dragging your bend downward will darken existing pixels. The actual pixels in your image beingness lightened or darkened depends on the location of the changes you are making on your curve. This is where nodes come in.

Creating a Bend

A node is a bespeak you create on your curve. You can create a node without moving the curve by ctrl+clicking on the curve where you lot'd like to add a node (as demonstrated by the node pointed out by the red pointer in the higher up photo). You tin can remove the node by clicking and dragging it outside the grid. (I clicked the "Reset Aqueduct" button to reset the bend back to its default position)

If you want to create a node and have the curve snap to the node, just click anywhere on the filigree (as I did with the node denoted by the scarlet arrow in the image to a higher place). (Once once again, I clicked the "Reset Aqueduct" button to reset the curve back to its default position)

For example, permit's say I wanted to make an aligning to the surface area I pointed out that contains a lot of darker pixels. I desire to make these pixels lighter. I tin can ctrl+click on my linear curve to create a node near that area (red arrow in the to a higher place photo).

Next, to brand these pixels brighter, I tin click and drag that node upwards (the blood-red arrow in the prototype above shows the node's new location). As I practise this, the diagonal line volition first to bend and become a curve.

You'll notice my epitome now appears lighter. This is because all of the areas (highlighted with yellow stripes in the image to a higher place) where my curve is angle up away from the original diagonal line are at present existence made lighter. The further away the bend is from the original line (green arrow denoted the original diagonal line), the lighter the pixels will be.

If I mark the original point where this pixel is on my Input range (green dotted line leading to a red dot), and and so mark the new point where it is on my Output range (green dotted line leading to a blue dot), you'll meet that the pixel is now closer to the white portion of the Output range than it was on the Input range (where information technology was closer to black). This is more than obvious in the "Input" and "Output" fields below the bend, which display the exact numerical value of the node. The Input was originally 17.12, just we moved it upwards so at present the Output value is 29.eleven.

Information technology is important to note that because this is a curve, there are many pixels that will be affected by the change. Still, you can mitigate some of these affects by creating more points along the curve. More on this in a moment.

I tin can reset my curve on the Value channel by clicking the "Reset channel" button above the grid (cherry pointer in the image above).

Adjusting the Effulgence

For those of yous familiar with the Levels tool, you'll remember that you lot can adjust the shadows and highlights sliders (reddish arrows in the photograph above) so that your black point is fix to the darkest pixels in your histogram, and the white point is set up to the brightest pixels in your histogram. In this case, the blank spaces on the far-left and far-right of the histogram hateful that there are trivial to no pixels with these values.

With the curves tool, nosotros don't have sliders for the shadows and highlights. Instead, we have endpoints for our curve. We can use these endpoints to create essentially the aforementioned effect as the levels tool.

For example, to change the blackpoint of our prototype with the curves tool, I can click and drag the node in the bottom left corner (blue arrow in the photo higher up) of the filigree to the correct (making sure it stays on the bottom of the grid). What this does is increases the value on the Input range (the bottom gradient) while keeping the output range (the left slope) ready to black. Information technology'southward changing which original pixels in your image will at present correspond black pixels.

To change the white signal, I can click and drag the node in the top correct corner (ruby arrow) to the left – making certain the node stays at the top of the grid. This shifts the original Input range value to the left while keeping the output range value set to pure white. In other words, information technology is changing which original pixels in your image volition now represent white pixels.

This helps correct some of the effulgence and contrast bug the current image has, making it look slightly more appealing.

Now, with the new black and white points set, let'south say I wanted to once once more increase the value of those darker pixels that are spiking our histogram. This time, though, I want to ensure I don't also make my bright pixels brighter. To ensure this, I can first create what's called an anchor node at the indicate where I don't want my bend bending.

I'll ctrl+click on the area on my curve where I want the bend to stop bending (ruby-red pointer in the image above).

Next, I'll click on the area of my curve where I want to burnish my pixels. The curve will snap to that new point (blue arrow). The pixels to the correct of my anchor node have remained untouched, whereas the darker pixels are now brighter.

If I click the "Dissever View" selection (carmine arrow in the paradigm above), you can meet my new paradigm on the left side of the preview line (blue arrow), and the original on the right. I'll uncheck Split up View to plow it dorsum off.

Below the curve yous'll notice there are another settings. Kickoff, there is the Input and Output values (outlined in blue in the image above). These values, which I discussed briefly earlier, display the precise location of your node on the grid. The Input value is what the pixel value was earlier it was changed. The Output value is the new value. If the Output value is higher than the Input value, it means the pixel is brighter than information technology was originally. If the Output value is lower, it means the pixel is at present darker than the original. Finally, if the values are the same, it means the pixel value hasn't inverse.

Next to Input and Output values, you tin can select the type of curve yous want connecting each node. By default, this value will be set to "Smooth." This will draw a bend with polish lines that run through your nodes.

If you want the curve to be straight lines connecting your nodes, you lot tin can choose the "Corner" choice (cerise arrow in the image above). Note that merely the current active node will accept its bend changed. If you want to alter all curves to direct lines, yous'll have to click on each node and then click on the "corner" type. For this example, I clicked on the node on the left-side of the histogram and clicked the "corner" icon. The curves became straight, which slightly changed the wait of my epitome. I'll click "smooth" to alter it back.

Below these settings there is some other setting labeled "Bend type" (dark-green arrow in the photo to a higher place). By default, this is set to smooth – which uses the traditional method of calculation nodes to the bend to alter its shape. All the same, you tin also change the fashion to "Freehand" if you would prefer to hand draw the curve with your mouse or tablet.

At present that we accept a pretty practiced idea of how the curves tool works, let'south move on to the colour channels.

Adjusting Image Colors

I'll change the channel I am working on from "Value" to our kickoff color, "Ruby" (red pointer in the photo above).

The Scarlet channel – and all colour channels for that matter – works a footling differently than the Value channel. Instead of making pixels brighter or darker, making changes to the Output range value will either make that pixel more saturated with red, or more saturated with cyan.

This is why the Output range gradient on the left side of the Histogram (greenish arrow in the epitome above) goes from red to black rather than from white to black (although, in my stance, the gradient should probably get from red to cyan).

For the Input range (blue pointer), the left side represents how much blood-red is in the darker pixels (shadows) in the epitome, while the right side represents how much red is in the brighter pixels (highlights) in the prototype. The taller the confined in the histogram, the more than instances there are of red in those pixel values.

For this paradigm, you'll see the histogram is skewed left (highlight by green in the above image), which means at that place are more than reds in the shadows of the epitome than the highlights, also as a big fasten of red nearly the darker end of the histogram (blue arrow). There is a large gap on the far correct, indicating there isn't much red in the highlights of the image.

If I wanted to add together cyan to the shadows of the image, I could ctrl+click to create a node on the left side of the curve (blue arrow in the photo higher up). I'll also ctrl+click to create an ballast node in the middle of the curve to make sure I don't add cyan to the highlights (green arrow).

Now, if I click and elevate the node downwards (green pointer in the photo above), cyan will be added to the shadows of my epitome. The ballast node (red arrow) keeps the rest of the curve anchored to the original linear curve.

I tin can also add together ruby to the highlights of the prototype by clicking to create a third node to the right of my middle node, then dragging this node upwards (blue pointer).

I'll now move on to the greenish aqueduct (blue arrow in the image above).

The aforementioned rules apply here – except lowering the output value will add magenta to the image, while raising the output value will increase the saturation of green.

In this case, since I am OK with adding magenta throughout all pixel values of the image, I will merely create a single node and drag it downwards (blood-red arrow in the image higher up). This will add more magenta saturation to areas near the node, and will however add a more than subtle amount of magenta to the highlights of my epitome.

Finally, I switch my channel to the blue channel (red arrow in the prototype above). Increasing my output value volition add blue saturation to pixels in that corresponding area of the histogram, and decreasing output values will add yellow saturation.

The histogram for the blueish channel shows me that there is a spike in blue in the shadows of my paradigm. Similar to the green channel, I'll correct this by adding a single node well-nigh that spike (red pointer in the image in a higher place). I too lowered the output value for the highlights by dragging the far-right node down a little bit on the far-right side of the filigree (light-green arrow). This tells GIMP that the brightest pixels in my image will incorporate less blue (the input value of 100 was reduced to 90.68).

If I wanted to salve these adjustments equally a preset and so that I could hands access them for another image, I tin can click the "+" icon adjacent to the Preset dropdown box (ruddy pointer in the prototype above). This will prompt me with a dialogue to fix a proper noun for the preset (green arrow). I went with "Basic Curves Adjustment" as the name. Click OK. Now this preset is stored in the preset dropdown for hereafter use.

When I'thou ready to apply my changes to my bend, I'll click OK. The epitome at present appears to be balanced ameliorate in terms of brightness and color.

I can make additional correction to the image with another instance of the Curves tool. I'll once again get to Colors>Curves (red arrow).

This time, I want to add some more than contrast to my image. To do this, I can create what'due south called an "Due south" curve. This bend shape is very commonly used to darken your shadows and brighten your highlights, which will add universal contrast to the image.

To create this shape, I tin can simply add together a node towards to shadows of the image and drag information technology downwards (cherry arrow in the prototype above). Adjacent, I'll add a node towards the highlights of my prototype and drag it upwards (green arrow). You'll come across our bend now resembles an "S."

If this creates too much contrast, you lot can likewise elevate the outermost nodes inwards towards the center of your grid to flatten it out a bit (red and green arrows in the image above).

A Split View (red arrow) shows our new image at present contains more contrast. I'll click OK to employ the changes.

A reverse S bend will practise the reverse – information technology'll make your shadows lighter and your highlights darker. This volition besides add together dissimilarity, but product a different result.

Inverting the curve (dragging the bottom left node to the very superlative and the superlative right node to the very bottom – cerise arrow in the image above) will produce the same issue every bit going to Colors>Invert.

The Curves tool is just i of several tools that tin can exist used to adjust the Brightness/Contrast and Colors of your prototype. It works all-time when combined with other tools like the Shadows-highlights tool, the Saturation tool, and a sharpening tool (equally I did to create the concluding prototype below).

That'due south it for this tutorial! Hopefully you liked information technology. If you did, yous can check out any my GIMP Help Articles, GIMP Video Tutorials, or GIMP Premium Classes and Courses.

Source: https://daviesmediadesign.com/how-to-use-the-curves-tool-in-gimp/

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