Why do contour and image give different results for the same data?

[nenyan]

When I use MATLAB to draw contour and color scale map of an array. The result is weird.

my code:
the first:
b=load('c:\...\b.txt');
contour(b)

the second:
b=load('c:\...\b.txt');
image(b)

The results are very different. I upload the array file and two figures.

 

[NemoReally]

When I use MATLAB to draw contour and color scale map of an array. The result is weird.

my code:
the first:
b=load('c:\...\b.txt');
contour(b)

the second:
b=load('c:\...\b.txt');
image(b)

The results are very different. I upload the array file and two figures.

I'm not a Matlab user, so I'm only guessing from the on-line documentation, but it may be that Matlab's image is treating your flat matrix as levels in the range 0-255 (or 63535). In which case, they are all to small to be distinguishable from 0. Try normalizing the data first - I've attached a Mathcad image (zoomed in slightly) to show what I mean (Mathcad converts reals to integers and shows a similar effect, which the function normalize overcomes)

 

[nenyan]

I'm not a Matlab user, so I'm only guessing from the on-line documentation, but it may be that Matlab's image is treating your flat matrix as levels in the range 0-255 (or 63535). In which case, they are all to small to be distinguishable from 0. Try normalizing the data first - I've attached a Mathcad image (zoomed in slightly) to show what I mean (Mathcad converts reals to integers and shows a similar effect, which the function normalize overcomes)

Thank you. After nromalization, it is still different.

 

[nenyan]

Oh, I got it. The y-axis is reversed.

 

[Number Nine]

You can use the imagesc() function instead of normalization. It will automatically set the scale range to the range of your data.