You can change some settings for image output and display for images generated from an Image Service. Depending on the type of data you have, along with requirements for quality, you may want to change some Spatial Server parameters. Because each site is unique, an image setting that performs well for one site may not work as well for another site.

Changing JPEG quality

The parameter jpegquality can be modified to change the quality of the JPEG output. The value represents a percentage value from 0 to 100, where 0 is the lowest quality and 100 is the best (default is 85 percent). The higher the value, the longer it takes to generate the image. This value does not signify the amount of compression.

The following table shows output file size and output generation time based on the JPEG quality setting. The output generation time is available in the Image Server log files. This benchmark is based on an image 800 x 600 with six vector layers. The file size and output time should be considered relative to each other since results will vary depending on the size and type of data used in a map.

jpegquality	Image size (kb)	Output time (sec)
50	146	0.047
60	164	0.047
70	189	0.047
85 (default)	256	0.062
90	304	0.078
100	668	0.078

Changing the PNG compression

The parameter pngcompression is a compression value from 0 to 9, where 0 indicates no compression and 9 indicates the highest compression. The higher the compression, the longer it takes to generate an image. The default value of -1 is equivalent to a compression value of 6.

The following table shows output file size and output generation time based on the PNG compression setting. This benchmark is based on the same 800 x 600 image with six vector layers used for the JPEG benchmark. The file size and output time should be considered relative to each other.

pngcompression	PNG8 Image size (kb)	PNG8 Output time (sec)	PNG24 Image size (kb)	PNG24 Output time (sec)
0	471	0.047	1410	0.109
1	70	0.032	110	0.109
2	63	0.047	100	0.109
3	56	0.063	88	0.137
4	54	0.062	80	0.141
5	48	0.062	74	0.156
6, -1 (default)	45	0.094	67	0.203
7	44	0.140	67	0.219
8	41	0.359	66	0.453
9	41	0.766	63	1.22

Changing the type of GIF output

The parameter interlacedgif specifies whether the images are interlaced or non-interlaced. An interlaced GIF first appears in a pixilated form before the higher resolution image is displayed. It provides an early cue to your user that an image is on the way. This setting does not affect performance. The output size and generation time, whether interlaced or not, is entirely dependent on the data source.
True = interlaced (default).
False = no interlacing.

Changing image output parameters