Encoding Statistics

Warning: this page is quite out of date now.

As part of encoding improvements (mostly in #419), we have collected encoding performance statistics for 4 still test pictures using the current crop of codec code (pre-release version 0.13).

These encodings are also used when a video encoding is selected as primary encoding, this is done to optimize bandwidth and CPU usage: video encodings require a full frame every time, so we use still picture encodings for smaller regions and for automatic lossless refresh.

Mode					Desktop 2560x1600		Browser 1920x1080		Diagram 640x800		Small Alpha 64x48
Encoding	Compressor	Preset	Quality	Speed	MPixels/s	comp	MPixels/s	comp	MPixels/s	comp	MPixels/s	comp
png	PIL (old)	optimized		0	1.6	8.1
png	PIL (old)			100	6.5	8.5
png	PIL			100	11.6	10.0	16.1	3.1	14.6	5.0	6.0	30.1
png/P	PIL			100	21.8	4.7	17.2	9.0	23.9	3.9	2.2	14.0
png/L	PIL			100	24.3	3.8	31.1	1.4	29.7	2.6	7.6	4.7
webp	PIL		0		5.5	0.5	6.3	0.5	5.9	0.7	0.4	13.4
webp	PIL		50		5.1	2.1	6.0	1.1	5.6	1.6	0.4	16.7
webp	PIL		100		4.3	6.2	5.9	3.1	5.3	4.3	0.4	28.8
jpeg	PIL	optimized	0		71.0	0.5	68.5	0.4	80.6	0.5	16.6	3.2
jpeg	PIL		50		86.0	3.1	68.1	1.9	68.2	2.5	12.7	8.8
jpeg	PIL	optimized	100		48.0	10.8	56.8	5.7	56.0	7.7	9.5	26.1
jpeg	PIL		100		72.0	13.0	58.4	5.7	56.5	7.7	8.4	26.1
rgb	lz4			100	224.0	15.0	497.0	4.3	526.0	6.9	76.7	56.0
rgb	zlib			50	21.0	9.1	30.2	2.5	27.8	3.1	11.3	39.4
webp	python-webm		0		6.0	0.8	6.7	0.5	6.2	0.7	0.5	13.4
webp	python-webm		50		5.3	2.1	6.5	1.1	5.7	1.6	0.6	16.7
webp	python-webm		100		0.3	4.8	1.0	0.7	0.7	1.6	0.1	25.0
webp	Cython	TEXT	0	100	18.6	0.6	19.4	0.4	18.9	0.6	1.5	2.9
webp	Cython	TEXT	50	100	15.5	2.7	17.7	1.5	16.6	2.2	1.2	11.9
webp	Cython	TEXT	99	100	12.6	6.7	15.2	3.3	13.9	4.6	0.8	29.7
webp	Cython	TEXT + lossless	100	0	0.1	4.9	0.6	0.7	0.3	1.6	0.0	24.7
webp	Cython	TEXT + lossless	100	100	2.3	5.9	27.8	1.3	27.2	1.9	1.5	26.9

Notes

• all tests were performed on an AMD FX-8150 (octa-core 3GHz AMD CPU)
• video encodings are not included, and should generally be preferred to the single picture encodings shown here
• this shows both speed in mega pixels per second (higher is better), and compression ratio (lower is better)
• Low quality at low speed doesn't really make much sense, so some values have been omitted
• changing the webp preset does not affect speed or output size much, it probably does affect the perceived picture quality (seems best to stick with TEXT to ensure that text remains readable)
• The new webp encoder seems to perform about the same with speeds >50%, only low speed is really slow, and lossless is unbearably slow (it can take more than 30 seconds to encode a single frame using lossless + low speed!)
• quality is not the same for each encoder, some have lossless modes others not, etc..
• for data showing the differences between the various png compression types (HUFFMAN_ONLY, FIXED, RLE, FILTERED, DEFAULT), see ticket:419#comment:6

You can find a much more detailed analysis (but which is limited to lossy formats in YUV420 colourspace mode...) here: ​Lossy Compressed Image Formats Study