I made an error with the Hercules graphics.
Zak is designed to run in a 320x200 resolution. The Hercules graphics mode uses a 720x348 resolution. If you were to put the original graphics inside the Hercules mode, you would have a very small graphics window in the middle of your screen, so they had to use a scaler to make the graphics appear larger.
Since the game uses a 320-pixel horizontal resolution, there is little difficulty upscaling by 2 to 640. Since the horizontal resolution of the Hercules graphics is 720, this leaves the game with 80 empty pixels. As for the vertical resolution, the game actually seems to use 340 lines between the status bar, graphics window, commands and inventory. In the 320 modes, the graphics window has a height of 128 pixels. In the Hercules mode, the height is also a multiple of 2, 256 pixels. The text remains at 8x8 pixels and there are 8 rows of text on the screen for 64 pixels, either in 320 or Hercules modes. That leaves 8 unused vertical pixels for the 320 modes and 28 unused vertical pixels in the Hercules mode.
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