MATLAB: Colormap option does not work with imshow in MATLAB 2017a

colormapMATLAB

colormap option does not work with imshow in MATLAB 2017a.

Best Answer

It looks like imshow() now sets the axis colormap (it uses default if colormap is not specified). Axis colormap over-rides the figure colormap - this allows to have multiple axis with different colormaps.

colormap function sets figure's colormap by default when no handle is specified, but this is over-ridden by the axis colormap and you don't see any change.

To change the colormap you can use colormap(gca,jet), which will set colormap to the axis. Alternatively use image() instead of imshow(), which doesn't seem to set axis colormap and changing the figure colormap with the usual colormap jet has an effect on the image.

Related Solutions

MATLAB: How to assign the colorbar for a subimage in a figure in MATLAB 7.8 (R2009a)

The colorbar can be attributed to a subimage in the figure using the colormap function. To set the range of the colormap indexed by the colorbar, set its 'YLim' property to this range.

The following code illustrates this concept:

load trees 
subplot(1,2,1);
subimage(X,map);
subplot(1,2,2);
subimage(X,winter(64));
fullmap = [map;winter]; %map and winter for second image
colormap(fullmap);  %set colormap
colorbar('YLim',[size(map,1), size(map,1)+64]); %colorbar's ylimits correspond to winter

MATLAB: Using imwrite() to create a .bmp file with custom colormap

The colormap for the imwrite must be in the range 0 to 1.

When you imwrite with a colormap the data must be integral. If it is type double or single then 1 is subtracted from it and the result is converted to uint8. In other words the values must already be colormap indices.

You need:

Numcolor = size(myMap, 1);
Imgmin = min(MyImage(:)) ;
Imgmax = max(MyImage(:)) ;
mappedImage = uint8( (MyImage-Imgmin)./(Imgmax-ImgMin).* (Numcolor-1) ) ;

Then imwrite(mappedImage, myMap,...)

Best Answer

Related Solutions

MATLAB: How to assign the colorbar for a subimage in a figure in MATLAB 7.8 (R2009a)

MATLAB: Using imwrite() to create a .bmp file with custom colormap

Related Question