tmp.py

import bpy

D = bpy.data

# BlendDataImages.new(name, width, height, alpha=False, float_buffer=False)
image_object = D.images.new(name='pixeltest', width=4000, height=3000)

# image_object points to the newly created: bpy.data.images['pixeltest']
num_pixels = len(image_object.pixels)

# well, turns out pixels is a little bit of a misnomer.
print(num_pixels)  

# >>> 480000
# A number 4 timeslarger than the expected 120000 pixels. It appears that
# .pixels is a list of the RGBA values of every pixel in sequence.

print( bpy.data.images['pixeltest'].file_format )  
# >>> 'TARGA'    
# seems to be the internal default

print(image_object.pixels[:4])
# >>> (0.0, 0.0, 0.0, 1.0)

# drawing a pixel, changing pixel content
for i in range(4):
    image_object.pixels[0+i] = (1.0)