Implement clim_percentile for RGB

[ahuang11]

Addresses part of holoviz/hvplot#1251

from pystac_client import Client
from odc.stac import load
import numpy as np

client = Client.open("https://earth-search.aws.element84.com/v1")
collection = "sentinel-2-l2a"
tas_bbox = [146.5, -43.6, 146.7, -43.4]
search = client.search(collections=[collection], bbox=tas_bbox, datetime="2023-12")

ds = load(search.items(), bbox=tas_bbox, groupby="solar_day", chunks={})
da = ds[["red", "green", "blue"]].isel(time=2).load().to_array()
low, high = np.nanpercentile(da, (2, 98))
img = np.clip(da, low, high)
img /= img.max(["x", "y"])

import matplotlib.pyplot as plt
fig, axes = plt.subplots(2, figsize=(10, 10))
da.plot.imshow(ax=axes[0], robust=True)
axes[0].set_title("ORIGINAL; GOLD STANDARD")
img.plot.imshow(ax=axes[1])
axes[1].set_title("MIMICKED XARRAY")

import hvplot.xarray
da.hvplot.rgb(x="x", y="y", bands="variable").opts(clim_percentile=True, title="INTERNAL CHANGES") + \
img.hvplot.rgb(x="x", y="y", bands="variable").opts(title="MIMICKED XARRAY")

Now, I'm have trouble figuring out how to apply this logic into HoloViews internally.

I took a stab at it anyway, but it looks a little different than the original imshow with robust=True because imshow uses vmin/vmax of the colorbar, but colorbars aren't a concept in HoloView's RGB (I think), so I'm forced to clip?

[jlstevens]

... colorbars aren't a concept in HoloView's RGB

That is correct. Generally, colorbars only make sense when colormapping and RGBs are already mapped directly to colors.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 28.57143% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 88.67%. Comparing base (9e5f904) to head (326d8ab).

Files	Patch %	Lines
holoviews/plotting/bokeh/raster.py	28.57%	5 Missing ⚠️

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==========================================
- Hits        58554    58546       -8     
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[jlstevens]

What is frustrating here is that the concept of clim_percentile is so close to the right thing here - and yet a name involving clim is really quite confusing in the context of RGB(A) images.

I suppose this can be documented nicely but I am still not convinced this shouldn't be something handled at the hvplot level only. Alternatively, if we need this at the HoloViews level, maybe it should be implemented as an operation instead?

Again, it is really annoying how close this looks to be the right thing even though I do think the semantics are being muddied here!

[hoxbro]

Suggested change

	img = img / high * 255
	img = (img - low) / (high - low) * 255

Another thought as I don't think we are using the full range of the RGB.

[ahuang11]

Superseded in holoviz/hvplot#1291

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.