imagesc make all negatives values black

I have the following code which is part of a subplot series. I want to change it so that all negative values become a certain colour (preferably black). I am stuck as to how to achieve this.

figure(3)
subplot(3,3,1)
imagesc(coeffA40)
title ('A40 Coefficients')
caxis([minCoeff, maxCoeff])
myColorMap = hsv(256);
myColorMap(1,:) = 1;
colormap(myColorMap);
grid on
ax = gca
ax.LineWidth = .75
ax.GridColor = 'k'
ax.GridAlpha = .2
ax.XTick = [10 20 30 40];
ax.YTick = [10 20 30];
ax.XTickLabel = {'', '', '', ''};
ax.YTickLabel = {'','',''};
ax.TickLength =[0.0 0.0]
ax.XTickLabelRotation = 45

Thank you in advance for any help!

Answer 1

[Image Analyst]

Several ways. One is to create a temporary image

displayedImage = coeffA40; % Initialize
displayedImage(displayedImage <=0) = 0;
cmap = jet(256);
cmap(1,:) = 0; % Lowest gray level appears black.
imshow(displayedImage);
colormap(cmap);
colorbar;

Another might be to alter the colormap so that it applies between 0 and the max.

cmap = jet(256);
cmap(1,:) = 0; % Lowest gray level appears black.
imshow(coeffA40);
colormap(cmap);
colorbar;
caxis([0, max(coeffA40(:))]);

(Both of these are untested - just off the top of my head.)

[Robert]

Thankyou for your reply, both of the methods you suggested work well,however they also make all the NaN's black, I need the to remain white is it a geographical image)...

[Image Analyst]

Set the nans to the max value (or the white value) before display, something like:

displayedImage(isnan(displayedImage)) = max(displayedImage(:));

[Walter Roberson]

 image(coeffA40, 'AlphaData', double(~isnan(coeffA40)) )