Jet colormap to grayscale

[Guillaume CALMETTES]

Hello,

I am looking to convert an image saved with the jet colormap to grayscale.
I tried to play a bit with the color module of skimage, but for the moment I couldn't manage to to map the jet colormap to linearly go from dark to light shades of gray. The main problem when applying a basic rgb2gray conversion is that the min/max values (blue and red) converge to the same dark value in the grayscale image, while the mid-range values (yellow/green) become the brightest.

Do someone has any trick to convert a "jet image" to grayscale?

Thanks a lot

Guillaume

PS: I have attached a picture as an example if you're willing to play with it ;)

[Schönberger Johannes]

Hi,

this might be a way to achieve this:

1. create jet colormap
2. convert color map to HSV-space and sort according to hue
3. use sorted jet color map as lookup table / colormap for image

I hope this helps.

Johannes Schönberger

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[Guillaume CALMETTES]

Hi Johannes,

Thanks, I'll try!

Guillaume

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[Stéfan van der Walt]

Hi Guillaume

On Thu, Nov 22, 2012 at 8:08 PM, Guillaume CALMETTES
<guillaume...@gmail.com> wrote:
> Do someone has any trick to convert a "jet image" to grayscale?

Here's a snippet that does it by brute force lookup:

https://gist.github.com/4146612

Hope that helps!
Stéfan

[Guillaume CALMETTES]

Hi Stefan,

Works perfectly.

However, I'm not sure why but I had to initialize the jet colormap object to create the _lut array.

I replaced:
lut = plt.cm.jet._lut[..., :3]

By:
jet = plt.cm.jet
jet._init()
lut = jet._lut[..., :3]

Thanks a lot.

Guillaume

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