Le mercredi 06 janvier 2016 20:32:04, Jim Lacy a écrit : > Thanks Even. I was actually more curious about the quality differences of > jpeg2000, GDAL 1.11 vs 2.1. File size is important too, of course.
Quality and size are highly correlated. The JPEG2000 encoder honours quite strictly the compression ratio you ask for (QUALITY=12 means 1/12 of the uncompressed size. It is not an objective measure of the "quality" in the traditional meaning). So if naturally YCC=ON leads to better compression rate, when you ask for the same compression target, the quality will be better when YCC=ON. The naming of the "QUALITY" setting is a bit arguable indeed (I think I took inspiration from the same parameter name of the JP2KAK driver) > > I did some further tests. For example, in GDAL 1.11.2: > gdal_translate -of JP2OpenJPEG -b 1 -b 2 -b 3 -co "QUALITY=12" Kenosha.tif > Kenosha_gdal1_11.jp2 > > compared to GDAL 2.1: > gdal_translate -of JP2OpenJPEG -b 1 -b 2 -b 3 -co "QUALITY=12" -co > "YCC=OFF" Kenosha.tif Kenosha_gdal2_1_ycc_off.jp2 > > .... produces results that are visually identical. > > However, simply by turning YCC=ON (the default) in GDAL 2.1 produces > noticeably "better" images at higher zoom levels. gdal_translate -of > JP2OpenJPEG -b 1 -b 2 -b 3 -co "QUALITY=12" -co "YCC=ON" Kenosha.tif > Kenosha_gdal2_1.jp2 > > It's interesting to me that the simple addition of YCC=OFF can noticeably > affect the visually quality of the output image. I certainly don't claim > to understand the nuances of jpeg2000! > > If you have time/interest, my test files are here: > https://uwmadison.box.com/s/xfc2f0ehwe6x6nu7chxu3ykvmk46mw85 > > Thanks again. > > > -----Original Message----- > From: Even Rouault [mailto:[email protected]] > Sent: Wednesday, January 06, 2016 4:25 AM > To: [email protected] > Cc: Jim Lacy > Subject: Re: [gdal-dev] GDAL 1.11 vs 2.1 and JPEG2000? > > Le mardi 05 janvier 2016 18:51:03, Jim Lacy a écrit : > > Can anyone with knowledge of the JP2OpenJPEG driver confirm or deny > > the following observation? > > > > I've been generating jpeg2000's in both GDAL 1.11.2 and GDAL 2.1. > > With all settings the same, I've noticed the visual quality of the > > images generated in GDAL 2.1 are noticeably "better." (a subjective > > term, yes) > > > > To my eyes, in 1.11.2, -co "QUALITY=20" yields results visually > > comparable to roughly -co "QUALITY=12" in GDAL 2.1. Win32 platform, > > binaries from gisinternals.com. > > > > Are there significant improvements in the 2.1 driver that would > > explain my observation? > > Jim, > > Checking the NEWS, I believe this might be related to this improvement I > did in GDAL 2.0 > > * add YCC creation option to do RGB->YCC MCT, and turn it ON by default > (#5634) > > And a quick test confirms it with a BMNG 21600x21600 3 bands : > > $ gdal_tanslate in.tif out1.jp2 -of jp2openjpeg $ gdal_tanslate in.tif > out2.jp2 -of jp2openjpeg -co YCC=OFF $ ll out1.jp2 out2.jp2 -rw-r--r-- 1 > even even 111977681 2016-01-06 11:07 out1.jp2 > -rw-r--r-- 1 even even 151981743 2016-01-06 11:08 out2.jp2 > > RGB->YCC MCT conversion is a step that occurs before other processings, > RGB->which > tends to decrease the size of the resulting file, all other things equal. > This transform is not completely lossless when using the default lossy > compression (there's a lossless version that is used when using -co > QUALITY=100 -co REVERSIBLE=YES), but the differences in pixel values tend > to be very small between YCC=ON/OFF. > > Even > > -- > Spatialys - Geospatial professional services http://www.spatialys.com -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
