This Image2LCD software (https://www.buydisplay.com/default/image2lcd) converts images to c-arrays. I want to write this basic operation myself, but I dont understand why the software outputs an array of length 5000 for an input image of size 200x200. For 400x400 the array size is 20000. It seems like its always 1/8 of the number of pixels.
The output array for the square 200x200 image begins and ends like this:
const unsigned char gImage_test[5000] = { /* 0X00,0X01,0XC8,0X00,0XC8,0X00, */
0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,
0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,
0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,
0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,
0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X60,0X00,0X00,0X00,0X00,
0X3C,0X60,0X00,0X0C,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,
0X00,0X00,0X00,0X00,0X70,0X00,0X00,0X00,0X00,0X7E,0X70,0X00,0X0E,0X00,0X00,0X00,
0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X78,0X00,0X00,
0X00,0X00,0X7F,0X78,0X00,0X0F,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,
0X00,0X00,0X00,0X00,0X00,0X00,0X7F,0XFC,0X3C,0X3E,0X3C,0X3F,0XF8,0X3C,0X7F,0X00,
0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X7F,
...
,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,
0X00,0X00,0X00,0X00,0X00,0X00,0X00,0X00,};
(Yes there is a lot of white in the image.)
Why don't you need one value for each pixel?
Shooting from the hip here, but if you're using monochrome, you only need one bit per pixel (Byte = 8 bits). These bits can be packed into bytes for storage efficiency. Say the first 8 pixels of your image are these:
0 1 0 0 0 0 0 1
If we interpret these eight bits as one binary number, this is 1000001, which is 65 in decimal - so just storing 65 in an 8-bit integer, taking up only one byte, will store all 8 monochrome pixels. The downside is that it's not as intuitive as having each pixel as a separate value in the array.
I may be wrong, but 1/8th points straight to this kind of compression.