pngjs | Simple PNG encoder/decoder | Image Editing library

I am trying to create a 16bit heightmap png from a 32bit Rgb encoded height value png.

According to mapbox I can decode their png pixel values to height values in meters with this formula. height = -10000 + ((R * 256 * 256 + G * 256 + B) * 0.1)

I am new to understanding this type of information and have tried to figure it out myself but I need some help.

I found this program called image-js, docs for this program are here . Note I am using this in the browser not with node.

I think it has the abilities that I need. However, I am really not sure how to get the data from the original image and create a new 16bit png with the new height values calculated from the above formula.

If you look in the docs under image I can set many properties such as

bitDepth and set that to 16

getPixelsArray() this function will give me an array of pixels values in the form of r,g,b. I think I can then run each pixel through the above formula to get the height. After that how do I turn this height data back into a 16bit grayscale heightmap png?

Thanks!

Example images. 32bit Rgb encoded height value png

16 bit heightmap png. You have to zoom in to see the image changes

Update:

Thanks to traktor for the suggestion. I wanted to add some information to my question.

I don't necessarily need to use image-js. My main goal is to get a 16 bit heightmap from a 32 bit RGB. So any other browser side javscript method would be fine. I also am using browser side createWritable(); stream to write file to disk.

I have a method used from this nice module https://github.com/colkassad/terrain-rgb-height however I cannot get the browser side version of pngjs to work correctly. I think there is a difference between browser side stream reader/writers and node reader/writers that make it not work.

Thanks!

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