Custom Image HoverTool with mask labels

Hi all,

Could anyone provide some guidance on how to show the x, y coordinates, pixel intensity and label based off of an external segmentation mask (e.g. background = 0, dog = 1, cat = 2, etc.) when hovering over a pixel in an image?

Similar to this:

Hi @JeffreyWardman,

The solution to your problem is similar to what I showed. The trick is creating your own custom function and linking the z parameter to a new function that you write. Here is an example:

import numpy as np
import holoviews as hv
from holoviews import opts
hv.extension('bokeh')
from bokeh.models import HoverTool
from bokeh.models import CustomJSHover
ls = np.linspace(0, 10, 200)
xx, yy = np.meshgrid(ls, ls)

MyCustomZ = CustomJSHover(code='''
        var value;
        var modified;
        if (value>0)
            {modified="positive";}
        else
            {modified="negative";}
        return modified.toString();''')

MyHover1 = HoverTool(
    tooltips=[
        ( 'intensity', '@image{custom}'),
   ],
    formatters={
        '@image' : MyCustomZ,
    },
    point_policy="follow_mouse"
)

img = hv.Image(np.sin(xx)*np.cos(yy)).opts(tools=[MyHover1])
img

The output looks like this:
image

The cavate is that the image intensity - the the z value, is called image so the name of the parameter in the hover tool must be @image.

Hopefully this example is good enough to resolve your problem.

Not exactly. I want to use an external mask. So it’s either use an Overlay of the image and mask, in which case I have two separated HoverTools and can’t seem to distinguish between the two when using ATimage once joined. Or, I need to add both ATx and ATy to the same custom JS hover, which I can’t quite figure out how to do.

The ideal circumstance would be something like

CustomHover = HoverTool(
tooltips=[
( ‘(x, y)’, ‘($x, $y)’),
(‘Intensity’, ‘ATimage.image’),
(‘Label’, ‘ATmask.image’),
],
formatters={
‘(x, y)’ : ‘numeral’,
‘Intensity’: ‘numeral’,
‘Label’: ‘numeral’,
},
point_policy=“follow_mouse”
)

img = hv.Image(img_array, label=“image”)
mask = hv.Image(mask_array, label=“mask”)
img_mask = Overlay(img, mask)
img_mask.opts(tool=[CustomHover])

AT = at symbol

If you can use Raster instead of Image (else the conversion of x, y into indices is a little bit more complex) you can try this:

import numpy as np
import holoviews as hv
from bokeh.models import HoverTool, CustomJSHover, ColumnDataSource

hv.extension('bokeh')

hv.opts.defaults(hv.opts.Raster(invert_yaxis=True)) # cf https://github.com/holoviz/holoviews/issues/4666


data = np.random.rand(10,10)
mask = np.random.choice(('dog', 'cat'), size=10*10, replace=True).reshape(10,10)
cds=ColumnDataSource(dict(mask=mask))
MyCustomZ = CustomJSHover(args={"cds":cds}, code='''
    const idx = Math.floor(special_vars.x)
    const idy = Math.floor(special_vars.y)
    return cds.get_array("mask")[idy][idx]''')

MyHover1 = HoverTool(
    tooltips=[
        ('x', "$x"),
        ('y', "$y"),
        ('value', '@image'),
        ( 'Animal', '@image{custom}'),
   ],
    formatters={
        '@image' : MyCustomZ,
    },
    point_policy="follow_mouse"
)
hv.Raster(data).opts(hv.opts.Raster(tools=[MyHover1]))

hovertool

Perfect, thank you!