What is root-pixels.db used for?

My previous post (#3) was marked 'Correct', but now I've un-marked it. I mean, nothing in it is wrong, that I know of, but the original question still remains. - I just wrote a test to delete selected previews from preview.db, but NOT from root-pixels.db Now, nowhere that I can find is there a thumbnail being displayed - begging the question, is root-pixels.db a "write-only" database, or is there really some circumstance when they're read/used...

Thanks jarnoh,

It was a real trick for me to get the jpeg data in a useable form (using quote(columnName) syntax then translating format):

 
local sql = str:fmtx( "select quote(jpegData) from RootPixels where uuid='77833B11-7D7C-4F8C-BE57-805DB25657D9'" )
local imageData, errm = sqlite:query( db, sql, 0 ) -- zero => return raw data.
if not imageData then
    app:logWarning( "sql query error: ^1", errm )
    return nil
end

local b = {}
for i = 3, #imageData - 3, 2 do -- good stuff is in-between X' and trailing '.
    local c1 = imageData:sub( i, i )
    local c2 = imageData:sub( i + 1, i + 1 )
    local c = tonumber( c1..c2, 16 )
    app:assert( c ~= nil, "nil at ^1: ^2/^3", i, string.byte( c1 ), string.byte( c2 ) )
    b[#b + 1] = string.char( c )
end
local jpegData = table.concat( b, "" ) 

If anybody knows a better way (to get binary data from database, e.g. in the form of a lua string) - I'm all ears.

PS - I guess you only need the preview database if you'll be dealing with icc profile and such stuff.

Thanks again,

Rob