20060509-A Lab-based uniform color scale

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最新推荐文章于 2025-05-27 16:13:16 发布

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分类专栏： Steve on Image Processing MATLAB

本文链接：https://blog.youkuaiyun.com/qiudw/article/details/25332341

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本文介绍了如何在MATLAB中创建一个均匀的色彩尺度，并详细解释了选择有效色彩尺度的四个设计原则。通过在L*a*b*颜色空间中定义路径并将其转换为sRGB色彩空间，实现了色彩映射。此外，还提供了使用该色彩尺度查看Radon变换图像的应用实例。

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原文：http://blogs.mathworks.com/steve/2006/05/09/a-lab-based-uniform-color-scale/

DSP Tips & Tricks

McNames gives four design principles for selecting an effective color scale (orcolormap, in MATLAB terminology):

"[The] color scale should cover as much of the range of available colors as possible, subject to the constraint that the luminance increases monotonically (for gray scale publications).
"Neighboring colors throughout the scale should be as distinct as possible."
"The perceptual difference between two colors should be approximately proportional to the difference between their positions along the color scale."
"The color scale should be intuitive."

A path through Lab* color space

Let's make a color scale that is a uniform ramp in L*. In the a*-b* plane, trace a semicircular path of radius 50, with angle varying between 0 and pi/2.

radius = 50;
theta = linspace(0, pi/2, 256).';
a = radius * cos(theta);
b = radius * sin(theta);
L = linspace(0, 100, 256).';
Lab = [L, a, b];

Now convert the L*a*b* values to sRGB so we can use it as a MATLAB colormap. Use the Image Processing Toolbox functions makecform and applycform.

map = applycform(Lab, makecform('lab2srgb'));

Radon example

Let's use this colormap for looking at a Radon transform image.

I = zeros(100,100);
I(25:75, 25:75) = 1;
theta = 0:180;
[R,xp] = radon(I,theta);
imshow(R,[],'InitialMagnification','fit')
colormap(map)

Color scale function on MATLAB Central

The function color_scale on MATLAB Central lets you easily create color scales like this. You can choose different values for the radius and the starting angle, and you specify a clockwise or counterclockwise path through a*-b* space.

colormap(color_scale)

Color scale GUI

The same MATLAB Central submission contains the color_scale_tool function, which is a GUI that lets you control the color scale parameters with sliders. It also shows you both the color scale and the approximate grayscale equivalent.