First of all, my question is different to How do I convert image to 2-bit per pixel? and unfortunately its solution does not work in my case…
I need to convert images to 2-bit per pixel grayscale BMP format. The sample image has the following properties:
Color Model: RGB
Depth: 4
Is Indexed: 1
Dimension: 800x600
Size: 240,070 bytes (4 bits per pixel but only last 2 bits are used to identify the gray scales as 0/1/2/3 in decimal or 0000/0001/0010/0011 in binary, plus 70 bytes BMP metadata or whatever)
The Hex values of the beginning part of the sample BMP image:
The 3s represent white pixels at the beginning of the image. Further down there are some 0s, 1s and 2s representing black, dark gray and light gray:
With the command below,
convert pic.png -colorspace gray +matte -depth 2 out.bmp
I can get visually correct 4-level grayscale image, but wrong depth or size per pixel:
Color Model: RGB
Depth: 8 (expect 4)
Dimension: 800x504
Size: 1,209,738 bytes (something like 3 bytes per pixel, plus metadata)
(no mention of indexed colour space)
Please help…
Best Answer
OK, I have written a Python script following Mark's hints (see comments under original question) to manually create a 4-level gray scale BMP with 4bpp. This specific BMP format construction is for the 4.3 inch e-paper display module made by WaveShare. Specs can be found here: http://www.waveshare.com/wiki/4.3inch_e-Paper
Here's how to pipe the original image to my code and save the outcome.
Contents of
4_level_gray_4bpp_BMP_converter.py
:Edit: everything about this e-paper display and my code to display things on it can be found here: https://github.com/yy502/ePaperDisplay