go - Generate 1 bit depth BMP image

Question

I need to create a mono bitmap image with a colour depth of 1 bit, for example:

$ file exampleMono.bmp 
> exampleMono.bmp: PC bitmap, Windows 3.x format, 640 x 1000 x 1

In Go, I'm able to generate a simple bmp image with the following:

tempPal := color.Palette([]color.Color{
    color.Black, color.White,
})
img := image.NewPaletted(image.Rect(640, 1000,0,0), tempPal)
filename := fmt.Sprintf("img-%d.bmp", time.Now().Unix())
file, _ := os.Create(filename)
bmp.Encode(file, img)
file.close

However, the resulting bmp file has a colour depth of 8-bits.

$ file img-1611574755.bmp 
> img-1611574755.bmp: PC bitmap, Windows 3.x format, 640 x 1000 x 8

I've had a look through the bmp, image and draw packages in Go and haven't found anything that appears to provide the ability to set the colour depth to 1 bit. Is it possible to achieve what I need in Go and if so, how?

question from:https://stackoverflow.com/questions/65884109/generate-1-bit-depth-bmp-image

Answer 1

As you can see from here down; golang.org/x/image/bmp's Encode() does not support bpp=1 in any of image modes.

It should be easy to take pieces from Encode() and write your own one-purpose encoding function as BMP file format and all its variants are well documented. BMP file format specs: on Wikipedia or FileFormat.