I am trying to write a monochrome image to PNG file using libpng library. PNG specification says that you can use grayscale type, since I do not need shades I want to use only grayscale, without alpha channel. So, the color_type parameter is PNG_COLOR_TYPE_GRAY.

I am having trouble to figure out how to write data from array of pixels to row_pointer. So that I can use png_write_image(png, row_pointer);.

If I have image pixels as array of bytes byte imagePixels[25] = {1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0};. This should represent image that is 5x5 pixel dimension. Pixel with value 1 should be black - #000000, and pixel with value 0 should be white - #FFFFFF.

In libpng library specification, it states that row_pointer is a array of rows. For my imagePixels variable array should be array of the five elements - row_pointer[5].

How do I write pixels from imagePixels to row_pointer array? I can not figure it out how to write data to row_pointer array.

Definition of row_pointer is:

typedef unsigned char png_byte;
typedef png_byte * png_bytep;

png_bytep *row_pointer;

Thanks for any kind of help or suggestion.

Edit:

Code is:

row_pointers = (png_bytep *)malloc(sizeof(png_bytep) * m_height);

for (int y = 0; y < m_height; y++) {
    row_pointers[y] = (png_byte *)malloc(png_get_rowbytes(png, infoPng));
    row_pointers[y] = (png_bytep)&(imagePixels[y * m_widht]);
}
png_write_image(png, row_pointers);