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How do you convert a 32bit RGB png with encoded height values to 16 bit png using browser side javascript?

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 enter image description here

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

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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