How to get the RBG values from a matlab figure?

Hi, I am with a problem and I couldn't find a solution so far. I generated some figures from previous data and now I want to extract some information about the figures.

Here is an example:

So I have a random data with 10 different values, each values may be represented by 3 values (R,G,B). I just want to get the RGB value for all the 10 values.

For instance: RGB for the 4th sample = [0.06275 0.4706 0.8549].

How to proceed this without using the data cursor?

Thanks,

[Jan]

"without using the data cursor" is not exactly enough: Why don't you wnt to use this simple tool? Should this happen without using the mouse, perhaps because you have to process 10'000 images automatically?

It might be much easier to extract the data from the axes objects instead of parsing the RGB colors.

[ArthurHB]

Hi Jan,

I want to proceed with this automatically instead of use the data cursor because I will have to do it a lot of times for larger figures.

Answer 1

[Adam]

If you have the handle to your image, hImage, then

hImage.CData

will give you the data (if you don't then use hImage = get( gca, 'Children' ) to get the image handle );

However, your image looks like it is just an indexed image where the colour is coming from the colourmap (Parula) being applied. So if you really want the RGB images you will have to create a parula colourmap e.g.

cmap = parula(512);

and index into it after scaling your CData from 1 to 512 and rounding to the nearest integer (or whatever size of colourmap you wish)

[ArthurHB]

Hi Adam, thanks for the reply.

If I use CData, it will return the 'Index value' of my dataset. I want to get the RGB vector associated with this index.

Like I said before, based on my figure, the RBG value associated with the index 57.9 is [0.06275 0.4706 0.8549].

As I have several figures, with several indexes, I would like to get automatically all the RGB vectors for all the indexes. As Matlab can display it with the data cursor, this information is stored elsewhere, but I can't get it so far.

[Adam]

That is what the 2nd part of my answer was about. The index value is an index value into a colourmap. You need to create that colourmap and index into it to get the RGB value. If you change the colourmap then the RGB value will change too as your image does not have fixed RGB values, only greyscale/index values.

I don't know what the range of your CData is or how you are scaling your colourmap, but if your CData is scaled to e.g. 1-512 then when you get that index of 57.9 out as, 'val' then

cmap = parula(512);
rgbVal = cmap( round(val),: );

will give you the RGB. You can create a parula colourmap of any size you want, though if your indices go up to huge values - eg. 32-bit you should scale down to a sensible range as a 2 billion element colourmap is pointless.

[ArthurHB]

Hi Adam, let's suppose that the colormap or the function that generated this colormap is not avaiable (or somehow has been generated randomly). So, I just have the figure and would like to get the [R G B] vector.

[Adam]

The colourmap must be available to have coloured the figure. If you have no colourmap you have no RGB values if you start with an indexed image.

[ArthurHB]

But it is possible that I receive some .fig file. In this case I don't have access to the original vector that created the colormap. However, I can access RGB values using the data cursor.

And that's what I want, to get these values. Thanks in advance.

[Adam]

There's always a colourmap with a figure, especially if it is not true RGB. The fig file just saves what was there at the time it was saved, it doesn't map the data onto the colourmap and then save it.

get( hFig, 'colormap' )

will give you the colourmap for the figure with handle hFig.