xooyoozoo Registered User

Join Date: Dec 2012 Posts: 199

JPEGs, WebP, HEVC huge amount of projects), especially at lower q levels. To try to quantify the discrepancy in performance, I ran a series of encodes through



Reference lossless RGB pictures from the MMSPG: Cafe, Car, Office, Plant, Woman



Code: convert 6.8.0-10 $f -define jpeg:dct-method=float -quality $i kdu_compress 7.1 -full -precise -i $f -rate $i webpe 0.2.1 -m 6 -segments 4 -q $i -pass 3 CS6 ExportOptionsSaveForWeb(); [ ... ] optimized = true; [ ... ] quality = i; HEVC10 Main_Intra -sr 128 -d 1 -dqd 3 -aq 1 --SAOLcuBoundary 1 -q $i JPGs were also ran through ImageOptim ( JpegOptim + jpegrescan + jpegtran ) SSIM only accounts for luma.

FFMPEG's RGB -> i420 yuv default conversion is just off. There's an odd hue in some pictures that's fixed by one or more of "-sws_flags +accurate_rnd+full_chroma_int+full_chroma_inp"

For HEVC, luma channel of yuv output was compared directly against luma channel of yuv input. Matlab's RGB2Gray is apparently in disagreement with FFMPEG's various conversions, so I decided to sidestep the issue.

Matlab could directly read all other formats except for WebP, where the official libwebp decoder was used to create a PNG for input

Results:

Quote: Edit Old set of 6 individual graphs for the 6 refs above.



Aggregate performance relative to Photoshop over 24 image Kodak set + 8 of XR set:





Comparison of 3 well-used JPEG2000 encoders versus libJPEG (aka why good tunings matter):



It's perhaps best to read the graphs horizontally ("for this metric value, A needs X-percent less bpp than B")

Min-y value in a graph was chosen by Photoshop's jpegs at Quality=0

Max-x value was chosen by me trying to leave ~1/3 white space on the left

My own image checks agree with the larger (>5% bpp) gaps in the results

Anything less, where the lines are overlapping, my preferential ranking is then JP2000=WebP>psJPG>libJPG=HEVC. The first 3 have great visual weights, while libJPG's are non-optimal and HEVC has none to speak of.

IW-SSIM does surprisingly well in ranking the Woman picture, as faces can be tough. However, it doesn't sufficiently mark down HEVC for overdoing the 'makeup' effect.

HEVC really did do that well in everything but Cafe and Woman. It's going to be killer if they actually make a decent file format out of it and throw on some psy tweaks.

The main image formats' lines were interpolated out of an (unnecessary...) 59 points. HEVC's line was interpolated out of 6 points. PCHIP was used.

If anything particular point on a graph interests you, feel free to ask for image uploads. Just give the [ bpp*1280*1600/8 ] value. I should be able to find something close for all but HEVC (only 6 points).



Edit: I've noticed for a while now that Photoshop's SafeForWeb JPEGS were almost always superior to the ones by Libjpeg (used in aamount of projects), especially at lower q levels. To try to quantify the discrepancy in performance, I ran a series of encodes through IW-SSIM , which should approximate still-image quality quite well. I made a similar post on the ImageMagick forums a couple days back, but some comments I got elsewhere made me tweak the tests a bit (lossless sources, better WebP parameters, threw in HEVC for the hell of it).Reference lossless RGB pictures from the MMSPG: Bike Setup notes:Results:Results notes:If anything particular point on a graph interests you, feel free to ask for image uploads. Just give the [ bpp*1280*1600/8 ] value. I should be able to find something close for all but HEVC (only 6 points).Edit: Comparison pics in my post below Last edited by xooyoozoo; 2nd March 2013 at 21:24 .