Custom Color Map

[sammertime]

Hi there,

First off - I love this package/project..Thank you! : )

I've reviewed the custom color map issues raised prior (i.e. below) and have successfully implemented the interval colormap into my tiles using titiler, as described here:

#496

I've applied transparency to some of my intervals i.e. say for the following two intervals, the 295-296 range should be transparent:

[[294,295],[255,234,0,255]],[[295,296],[0,0,0,0]]

This is technically working, but transparency is returning as a black color in the tiles. My goal is to have intervals with the color [0,0,0,0] in my custom colormap return as completely transparent from titiler.

The query parameters I'm using with the tile endpoint are the following:

bidx=1&unscale=false&resampling=nearest&return_mask=true&colormap=[[[...]]]

My question is, is this something that can be achieved with titiler and, if so, can it be done by tweaking my query parameters? Or, is this a more involved fix in the underlying COG creation process?

Thanks so much..
S

[vincentsarago]

sounds like #525

I think the issue is that you are using auto formatting which sadly is decided before applying the colormap, if titiler don't see any mask value it will choose JPEG and then the [0,0,0,0] value will be black. If you force the image format to png it should be transparent. (I totally understand that it's not perfect, and we might try to fix this in rio-tiler at one point)

FYI: I'm moving this issue to discussion because without proper reproductible example I cannot understand if it's a bug or a feature.

[vincentsarago]

confirmed in the /map endpoint

http://127.0.0.1:8081/cog/map?url=test-file.tif&colormap=%5B%5B%5B-4%2C+0.2%5D%2C+%5B127%2C+17%2C+224%2C+255%5D%5D%2C+%5B%5B0.2%2C+0.7%5D%2C+%5B242%2C+238%2C+189%2C+255%5D%5D%2C+%5B%5B0.7%2C+14%5D%2C+%5B227%2C+5%2C+5%2C+255%5D%5D%5D

[vincentsarago]

oh and note that return_mask has to be set to true or the PNG won't have alpha band

http://127.0.0.1:8081/cog/map?url=test-file.tif&colormap=%5B%5B%5B-4%2C+0.2%5D%2C+%5B127%2C+17%2C+224%2C+255%5D%5D%2C+%5B%5B0.2%2C+0.7%5D%2C+%5B242%2C+238%2C+189%2C+255%5D%5D%2C+%5B%5B0.7%2C+14%5D%2C+%5B227%2C+5%2C+5%2C+255%5D%5D%5D&return_mask=False

[neelduttahere]

Hey so setting return_mask=true or not passing return_mask at all (since the default is true for it), gives a broken output as shown in the above responses. But for you it seems to work, I guess I need to look back into the dependencies installed, probably has to do with rio-tiler because last I remember we did have to downgrade rio-tiler for a specific issue. Will keep posted if anything arises

[neelduttahere]

@vincentsarago I notice that you are sending color information for each interval like this [[-4, 0.2],[127, 17, 224, 255]], instead of this [[-4, 0.2],[127, 17, 224, 1]]. I thought we send RGBA values against each interval, where the last number is for alpha (from 0.1 to 1). Either way [[-4, 0.2],[127, 17, 224, 255]] works amazingly! Though curious why we have to send 255 instead decimal alpha.

Thanks a lot!

[vincentsarago]

we have to send 255 instead decimal alpha.

That's a GDAL format, alpha value can be between 0 (transparent) and 255 (non-transparent).

https://cogeotiff.github.io/rio-tiler/colormap/