png encode is slow

[Vlad Merticariu]

Our png encoder is very slow compared to other formats (1 order of magnitude). This is problematic because in almost all cases a user wanting to display a 2D result on the web, will have to use png (jpeg doesn't support transparency).
I am testing below on an array of 8640 * 4320, type RGB, size ~110 MB.

Time to retrieve non-encoded: 0.50s
Time to retrieve jpeg-encoded: 0.87s
Time to retrieve tiff-encoded: 0.86s
Time to retrieve png-encoded: 4.61s

Queries and timings below.

time ./rasql -q 'select m[0:8639, 0:4319, 0] from perf m'
./rasql: rasdaman query tool v1.0, rasdaman 9.6.0.
Opening database RASBASE at localhost:7001… ok.
Executing retrieval query… ok.
./rasql done.
real 0m0.508s
user 0m0.108s
sys 0m0.040s
time ./rasql -q 'select encode(m[0:8639, 0:4319, 0], "jpeg") from perf m'
./rasql: rasdaman query tool v1.0, rasdaman 9.6.0.
Opening database RASBASE at localhost:7001… ok.
Executing retrieval query… ok.
./rasql done.
real 0m0.879s
user 0m0.036s
sys 0m0.016s
time ./rasql -q 'select encode(m[0:8639, 0:4319, 0], "GTiff") from perf m'
./rasql: rasdaman query tool v1.0, rasdaman 9.6.0.
Opening database RASBASE at localhost:7001… ok.
Executing retrieval query… ok.
./rasql done.
real 0m0.860s
user 0m0.048s
sys 0m0.068s
time ./rasql -q 'select encode(m[0:8639, 0:4319, 0], "png") from perf m'
./rasql: rasdaman query tool v1.0, rasdaman 9.6.0.
Opening database RASBASE at localhost:7001… ok.
Executing retrieval query… ok.
./rasql done.
real 0m4.618s
user 0m0.024s
sys 0m0.020s