How to color and light Matching In GIMP

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There are a lot of things to consider when creating an incredible looking photo composition, so in this article I will go through a full explanation of what to do and consider when creating an excellent looking photo composition, especially matching photos.
This video is intended for Gimp users, but it can also be useful for users of other software. The fundamentals are the same.

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But let’s understand what to consider when matching two or more images.

Match Luminosity level
Match saturation (only if your images have increased saturation).
Match color

Luminosity levels are important.

The first thing to consider is luminosity. Many beginners struggle with Luminosity issues in their work.

But before that, let’s understand what luminance levels are in a photo.

Luminance is basically the values of blacks, whites, and midtones in an image.

Now that you know what luminance is, let’s understand how it can help you match images.

There are many tools that let you change the luminance levels of an image.

  • Curves
  • Levels
  • Exposer

Curves let you adjust the image with much more control, but it looks harder to new beginners and the exposure is very simple with not much control, so our choice will be levels for this video, because it is very simple to understand.

So let’s use levels because it is easy and gives us a very good amount of control, but if you are already comfortable with curves, then you are free to use that.

But before we go to match luminosity levels, let’s understand that color often gives us the wrong idea of luminosity levels, so let’s disable the colors and only keep luminosity levels. After disabling the colors, your image will become black and white, and that’s what an image looks like without color.

To remove colors from your image non-destructively, you have to create a new layer, fill it with black, and then set the blend mode to lch color. After that, your image will look black and white. That means you removed color temporarily from your image.

Now you can see the luminosity levels of your image directly, so use the levels or curves to match the luminosity, but if this is first for you, then use the sample tool to sample dark points and bright points, and then if the bright point is higher than the target image, reduce the brightness, and if the dark point of the image is lower than the target image, lift up the dark points.

So in levels, the left point controls the dark part of the image, the right point controls the bright part of the image, and the middle one controls the midpoint of the image, meaning mid luminosity levels.

And the lower output controls the overall luminosity of the image, so moving the right controls will make your image’s bright part dimmer, and moving the left controls will make your image’s dark part brighter and less black.

To use this concept, you can sample the dark or bright point of the image to determine if you need to make the bright part brighter or dimmer, and same with the dark part and mid part.

You can check the luminosity levels in your image using the color picker. Simply by shift-clicking the part of the image that you want to check, and a small window will open on the side of your canvas and then change to HSV from RGB. Now you can see the luminosity levels in the v value. This means if part of the image is brighter, then it will give you a higher number, and if it is darker, then it will give you a lower number.

So you can use this method to match the luminosity of many images and it will work on almost every image.

So let’s use this technique in real image. First we use the color picker method to see the black and white values of the subject and background images. Now we know that we have to lift up the black value and darken the white values.

So let’s use levels to lift the black values and darken the white values. Both can be done with left and right control points.

Atmosphere

But now let’s understand how the atmosphere affects the luminosity of your image, especially their blacks value.

But why are we learning about the atmosphere? , because we live on a planet with an atmosphere, and understanding how the atmosphere works will help you when you are making environments/landscapes or want to give your composition depth.

First, let’s understand that as things go far from you, they fade and their luminance levels become much less prominent, meaning that the blacks values are starting to go toward white, and they also lose saturation, meaning that they seem to lose color as they go very far.

And another fact that can help you make a convincing environment is that the atmosphere is densest at the base of the surface, and as you go up in the sky, the atmosphere becomes thin, so you can also fade or make the black levels much less black in the base surface and slowly reduce the intensity in the upper portion of the environment but it will depend on what kind of environment you are trying to achieve.

So what this means:

The sky doesn’t need to change much of its lumenance because, as I said, the atmosphere becomes much less dense in the upper portion of the environment.

So now you know how the atmosphere affects levels, let’s learn how you can change Luminosity levels.

That’s it for matching luminosity. Let’s talk about color. Many times, after adjusting the luminosity, your image often becomes more saturated, so to reduce or increase the saturation, you can use hue and saturation color adjustment.

So now let’s start color matching.

Color matching

This can be a little difficult to explain, because there are many ways to match colors. Some are more detailed, and some might only help you to match the general feel of your composition.

We will be looking at the detailed method. But worry not, because I will be making this as simple as possible.

To match the color, you can use curves, levels, and color balance. Curves give you extra controls as always, but levels can give you much less compared to curves, and the easiest to understand is color balance.

So we will be using color balance to match the color, but you are free to use any other adjustment you are comfortable with. They all do the same thing. The only difference is how much control they provide.

But let’s understand color balance first.

Color balance has 3 sliders and 3 select ranges.

The 3 sliders represent 6 colors. On the right side of the slider you have red, green and blue, and on the left we have cyan, magenta, and yellow.

And 3 select ranges represent 3 area where color adjustment will happen, and these three are shadows, midtone, and highlights, all three thing are luminosity levels of the color that the slider will affect, meaning that if you adjust the top slider in the shadow range, then it will either increase red or cyan in darkest/shadow part image.

And if you do the same with any slider it will work according to its name, meaning if you change any color slider in highlights then it will affect color in the brightest area of the image, and doing same with mid tone will be the same in the midtones part of the image.

So let’s use color balance to match the color of our images, like how colors distracted in changing out luminance value, similarly luminance value can also distract in color matching process, but it will only distract you when you are new in color matching process, so assuming you all are new in color matching, so lets disable luminance value and only enable colors, so it can make it easy to match color.

To only enable colors create a new layer, fill it with gray then set blending mode to luminance, it will only show you the colors of your image.

So now, let’s use color balance, as i said name explain it what it does,

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