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Best Techniques for Gradient Map Color Toning

October 25, 2010 • By

In this post we’ll analyze a variety of useful techniques that will allow us to tone map an image for future print or web design projects.

You probably have your own way to color correct and alter the tone of an image in your preferred application, but there’s a huge reason why you should know more about gradient mapping: it’s cross compatible between applications and operating systems. If you understand the basic principle, you can use it in Photoshop, Gimp, Pixelmator and all other applications on Mac OSX, Windows or Linux. It’s a powerful technique also in video editing systems and generally where you want to alter the colors of an image.

Our Original Image

Original Image

This is the image that we’ll use for our gradient map toning examples. One thing is important: if you want to use the gradient map tool, and generally any tool that implies altering colors, avoid tweaking the exposure and brightness/contrast of the original image. Try to shoot the image as best as you can because you’ll be able to work on real pixel information. If you alter the exposure after the shooting a whole lot, you’ll loose a lot of details that will compromise the toning.

As you can see, it’s a simple shooting at Park Guell, in Barcelona, on a rainy day. Before you begin to go into Photoshop, let’s analyze the image. The important thing here is to understand three color zones that will make our tone mapping a breeze. You have to focus on highlights (areas that are brighter, getting to white), shadows (areas that are darker, getting to black) and midtones (areas that are between brighter and darker areas, getting to gray). It’s important to train the eye to understand differences between these areas so that you can target them easily with the gradient map tool.

The gradient map tool works in a really simple way: you choose a gradient and Photoshop will map the image with the gradient. The left color of the gradient will be mapped to shadows, the right color will be mapped to highlights and the middle area of the gradient will be mapped to midtones.

Let’s start with a self explanatory example.

Black & White Tone Mapping

Black And White

Extreme Black And White

Let’s add a gradient map adjustment layer in Photoshop, by clicking on the little circle icon in the bottom area of the layers panel, and selecting “Gradient Map”. This action will automatically add a Gradient Map Adjustment Layer with a predefined black to white gradient. As you can see, you get a black and white conversion of your image, since highlights are mapped with white and shadows are mapped with black. It’s a pretty boring black and white image. But let’s add a white color stop in the middle of the gradient and assign black to the left and right stops.

Now the effect is extreme, but useful to understand how the gradient map works. As you can see the subject of the photo is highlighted. Why? Because we pushed to the white all the midtones in the image, and since the monument in the original photo was having a lot of midtones areas, it’s entirely white now. The sky is black because the areas that in the original image were near white have been mapped to black. This is the power of the gradient tool. It’s intuitive and after a little bit practice you’ll be able to achieve a really professional color correction. The HEX color codes for this effect are #000000 to #ffffff to #000000.

X-Ray Tone Mapping

XRay

Now we can start experimenting with some colored gradients to give the image a distinctive and creative look. Obtaining a pseudo x-ray style with a gradient map is very simple. Just add a new gradient map layer with a gradient that starts at #020144 and ends at #95a2ce. With this gradient the image turned to blue, but you’re not actually seeing the x-ray effect. The secret is in the “reverse” option. By checking this option you reflect your gradient, and the tone mapping is reversed so dark areas will turn to light blue and bright areas will turn to dark blue. The final result is an x-ray color corrected image.

Warm Tone Mapping

Warm

In this section we’ll take the gradient map tool to another level by introducing the overlay blend mode and the opacity adjustment. As you can see from the image, the result is fairly better that previous effects. Let’s start from the gradient. In this case is a simple two stops gradient, from #ff0015 to #fff800. If you apply it before the effect you will soften the image and you’ll loose a lot of details.

The trick is, whenever you see that the gradient map is too visible, select the overlay blend mode for the current gradient map layer. This way the layer will be applied with the low contrast/high contrast method and the result will be more real and consistent. If it’s still too heavy, just decrease the opacity a bit (in this particular case 70% is fine) and the image will be warmed.

Cold Tone Mapping

Cold

As you can see from the image, in this case we have to choose some cold colors to achieve the opposite effect. A cold image is an image that has a color space defined by cold blue colors. In this particular case a simple two stops gradient will not work since the midtones of the monument would be too dark.

After experimenting with colors and stops, a good solution could be a gradient from #004170 to #9dd4fb to #bde9fa, with a middle color stop at 28%. This gradient will cool down the sky and the ceramic parts of the monument, while lighting up dark areas. The final result is a more dramatic image, that presents itself better than the original image due to the weather conditions of that particular rainy day.

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