Rasql_Wrong negative value in calculation

[Bang Pham Huu]

WCPS query

for c in (rgb) return encode( (unsigned char)(c.red - c.blue)[i(0:0), j(0:0)] , "csv")

with c.red[0:0,0:0] = 119 and c.blue[0:0,0:0] = 248

then (c.red - c.blue)[i(0:0), j(0:0)] = 119 - 248 = 127 ?

[Dimitar Misev]

But you do a cast to (unsigned char), what should be the proper result?

[Bang Pham Huu]

Sorry, actually the query does not need encode in "unsigned char", example below

for c in (rgb) return encode(  (c.red  - 248)[i(0:0), j(0:0)] , "csv")

will return {-129}

but

for c in (rgb) return encode(  (c.red  - c.blue)[i(0:0), j(0:0)] , "csv")

will return {127}

and I expected it should be negative number.

[Dimitar Misev]

The original types are unsigned char of c.red and c.blue, the minus operation doesn't automatically expand the types. You should cast both operands to short for example for this exapmle to work.

for c in (rgb) return encode(  ((short)c.red  - (short)c.blue)[i(0:0), j(0:0)] , "csv")