+--------------------------------------------------------------------------------------------+
Size comparison for 6x6 monochrome image ranking from best to worst

pattern.gif: 49 bytes
	- Dithering level: 7 (doesn't really matter)
	- Transparency threshold: 128 (doesn't really matter)

pattern.bmp: 86 bytes
	- Bit depth: 4
	- Dirthering level: 7 (doesn't really matter)

pattern.png: 151 bytes
	- Bit depth: 4
	- Dirthering level: 7 (doesn't really matter)
	- Transparency threshold: 192 (doesn't really matter)
	- Interlaced (saves 1 byte)

pattern.webp: 248 bytes
	- Quality: 100

pattern.jpg: 800 bytes
	- Chroma Subsampling: 4:2:2 (saves 6 bytes from 4:4:4)
+--------------------------------------------------------------------------------------------+

-- Here's the image used for the test --
data:image/gif;base64,R0lGODlhBgAGAHAAACwAAAAABgAGAIH////08v8AAAAAAAACCgRiGciL9mA6ExQAOw==


Unfortunately after all response headers are set, the total ends up at 317 bytes.