#Plot color matlab how to#

The objective of this article is to have a thorough understanding of Colors in MATLAB. MATLAB comprises a number of techniques and functions to perform the above-mentioned capabilities. 'EdgeAlpha',0.Hadoop, Data Science, Statistics & others % Pick the colors we want to use from the normal line color order. Utility functions function drawColorbar(rgb_colors)ДЄxis off end function plotrgb(x,rgb_colors)

#Plot color matlab how to#

Next time, I'll talk about how to draw the spectral color scale underneath the plot. RGB_lin = min(max(RGB_lin,0),1) Д¬onvert to nonlinear RGB values for the final resultД¬onvert to nonlinear sRGB values suitable for display on a computer monitor. RGB_lin = conv2(RGB_lin,ones(21,1)/21, 'same') Д®liminate small negative numbers and numbers slightly greater than 1 that have been introduced through floating-point round-off. This helps the spectrum to appear smoother, reducing sharp transition points. Smooth out the linear RGB curves to eliminate discontinuous first derivatives. Then, for each color, scale all components back down, if necessary, so that the maximum component value is 1.0. Next, to get brighter spectral colors, including a good yellow, scale up the linear RGB values, allowing them to get higher than 1.0. % No scaling is needed for component values that are already % nonnegative. Now, one component at a time, and for each spectral color, mix in a sufficient amount neutral gray with the same Y to bring negative component values up to 0. (Note: Young (2012) divides by a fixed value of 2.34.) RGB_lin = RGB_lin / max(RGB_lin(:)) The next thing we'll do is scale so that the maximum linear RGB value is 1.0. We want to modify those curves so that they fall within the range and produce a reasonably accurate, smoothly varying, and attractive representation of the spectral colors. Title( 'Linear RGB values for spectral wavelengths') RGB_lin = xyz2rgb(XYZ, 'ColorSpace', 'linear-rgb') The Image Processing Toolbox function xyz2rgb can optionally convert to linear values. The typical RGB values we see for image pixels are related nonlinearly to light intensity, and linear RGB values are more appropriate for the following averaging and scaling steps. Work with linear RGB valuesДЇirst, let's convert the XYZ values to 'linear' RGB values. The method is a variation of the one described in: Andrew Young (2012). I'm going to show you the method used by the DIPUM3E function spectrumColors. These out-of-range values are being clipped to the displayable range, and that leads to a bad results. Everything outside that range (negative values, or values greater than 1), can't be displayed exactly. The gray shaded region shows the range between 0 and 1 this is the displayable range of colors. (The plotrgb and shadeGamutRegion functions are down below.) close What's going on with this? We can see the problem if we draw a line plot of the RGB values.

It seems uneven, with several patches that seem to be mostly one color. That doesn't look like a very good spectral color plot to me.

It uses the DIPUM3E function colorSwatches.) Let's try simply converting these XYZ values directly to RGB using the Image Processing Toolbox function xyz2rgb. Title( 'XYZ values for spectral wavelengths')

Or we can find the XYZ values for all of the wavelengths we are interested in. To find the XYZ values for a specific lambda, such as 500, we can use interp1: interp1(T.lambda,500) But it is really simple: just interpolate into the CIE XYZ color matching functions, which are returned by the DIPUM3E function colorMatchingFunctions. This computation can be found in the DIPUM3E function lambda2xyz. The first computational step is to find the XYZ values for each value of lambda. Billmeyer and Saltzman's Principals of Color Technology, 3rd ed., John Wiley & Sons, NJ. The limits used here, 380 nm to 780 nm, are those given in Berns, R. What should the x-axis limits be on this plot? In other words, what is the visible wavelength that we are interested in? You will see different limits being used in different places. Convert to nonlinear RGB values for the final result.Find XYZ values for the spectral colors.