ArcGIS Sever 10.7.1: Which option for “image format” is the best when caching a map that contains vector and imageries data?
I couldn’t figure out which option for “image format” is the best when caching a map that contains vector and imageries data. The documents don’t provide precise answer on this particularly when comparing between jpeg and mixed options
Is jpeg or mxd better in this case?
It isn't a coincidence that MIXED was pre-selected by the software for you: Edit service caching properties in Manager—ArcGIS Server | Documentation for ArcGIS Enterprise
When you initialize a new cache, ArcGIS examines the layers in your map and selects a default image format for you. If your map contains only vector layers, the default is PNG. If at least one raster layer is detected, the default is MIXED.
But Esri does say the user should validate that the default makes sense with their data.
You should examine this default and determine if it makes sense based on the purpose of your map.
The question of whether one should use JPG, PNG, or some other format for an image isn't unique to Esri nor is it unique to building map caches. There are lots of websites, blogs, etc... that discuss the trade-offs between using various image formats to display various types of information. That said, I think Esri's documentation covers it best:
Before committing to an image format for a large cache, build a small cache of a representative area of your map and examine the tile quality and performance in a test application. If you are working with multiple caches, build a small test cache for each, and add them to a test application to make sure they overlay as expected. This allows you to make adjustments before you create the entire cache.
Despite the fact that “mixed” option is the default, I’m not sure if the jpeg is still better in transparency effect, cache size, pixel data loss, sharper image, or performance.
use PNG of one of the bit depths if you need transparency and png doesn't sacrifice image quality
But for which reasons jpeg could be a better option than png or mixed?
There is a lot of material but no precise answers
Time to run a test with both types and see if your people can "see" any difference in the images, then weigh the other factors. If they "look" the same, then appearance isn't a factor and you can place importance on things like the need for transparency, etc