Output of /preview different from output of /tiles for same image and colormap

[mghildiy]

I am serving a cog file. with titiler.

When I call /preview with a color map:

http://localhost:8001/cog/preview.png?url=http://localhost/cog/sgnp_fcd_3857_cog.tif&colormap=[[[0,15],[215,25,28,255]],[[15,20],[254,196,123,255]],[[20,40],[237,247,174,255]],[[40,60],[156,212,103,255]],[[60,80],[91,181,84,255]],[[80,100],[25,150,65,255]]]&max_size=1024

Image fetched is :

I apply same colormap in server:

FCD_INTERVAL_COLORMAP = [
    ((0, 15), (215, 25, 28, 255)),
    ((15, 20), (254,196,123, 255)),
    ((20, 40), (237,247,174, 255)),
    ((40, 60), (156,212,103, 255)),
    ((60, 80), (91, 181, 84, 255)),
    ((80, 100), (25, 150, 65, 255)),
]
cmap = default_cmap.register({"fcd_intervals": FCD_INTERVAL_COLORMAP})
ColorMapParams = create_colormap_dependency(cmap)
colormap  = ColorMapFactory(supported_colormaps=cmap)
app.include_router(colormap.router)
cog = TilerFactory(colormap_dependency=ColorMapParams)

I fetch image in my react app as:

data: 'http://localhost:8001/cog/tiles/WebMercatorQuad/{z}/{x}/{y}.png?url=http://localhost/cog/sgnp_fcd_3857_cog.tif&rescale=0,100&colormap_name=fcd_intervals',

But image is rendered pretty different:

What can be the reason for this difference when same colormap is applied on same image?

[vincentsarago]

because in the first one you're setting rescale=0,100

[mghildiy]

Thanks Vincent. It got it working.
A question here. How does rescale parameter influence the response? In this case, raster values actually are in range 0-100. In other cases, it may be some other range, like -0.6 -.7. So when do we actually need rescale parameter?

[vincentsarago]

well it depends on your input file 🤷‍♂️

I guess it might depends how you created your COG Overviews, if you used non-nearest resampling methods you might get values outside the 0-100 range