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Colorbar not plotting the right colours

Asked by Raymond Hoang on 30 Oct 2016
Latest activity Commented on by Image Analyst
on 31 Oct 2016
I'm having trouble using the colorbar/colormap functions. I create a test plot, plotting a bar graph from 0,0 to 100,100 and created a color bar. I would like the color bar to correspond to the y values of the graph. Which means, if looking at the xaxis, the graph would be colored in the same order as the colorbar from 0->100 by matching the y-values to the colorbar values.
It seems to be plotting the value 0 corresponding to the colorbar which is purple/black every time which I believe is the z-value. Mainly see colorbar/maps used for contour plots but I would like it to work for a 2D plot.

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2 Answers

Answer by Image Analyst
on 31 Oct 2016
Edited by Image Analyst
on 31 Oct 2016

Consider creating an indexed image instead of a bar chart. Then you can write each bar as a column with the gray level of the color you want. Apply the colormap and that column of pixels will show up in the desired color.
If you want a color gradient in each bar, then that is more complicated - you'd have to write a ramp of pixel levels rather than a constant pixel level that corresponds to the tallest color.
rows = 100;
columns = 100;
indexedImage = zeros(rows, columns, 'uint8');
for col = 1 : 100
row1 = rows-col+1
indexedImage(row1:rows, col) = col;
end
imshow(indexedImage);
colormap(gca, jet(rows));
caxis([0, rows]);
colorbar;
Modify as needed.

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Answer by Marc Jakobi on 31 Oct 2016

You cannot create a colorbar for bar() graphs in Matlab. What you can do is use a loop to create a separate bar graph for each color.
See this answer for an example.

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I'm not sure how to incorporate that answer with what I'm trying to do.
I have a function that is constantly outputting a value "y" but not putting it into a matrix form.
figure(1)
hold on
ylabel 'Temperature (Degrees)'
title 'Live Temperature Plot'
i = 0;
while true
[t] = ReadData(out)
figure(1)
if(i <= 100)
xlim([0,200]);ylim([0,100])
else
xlim([i-200, i]);ylim([0,100])
end
tempplot = bar(i,tc,'BarWidth',1);
i = i + 1;
pause(0.05)
end
See this link at 6:50
I'll show you. See my attached demo.

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