On Sunday, 18 January 2015 at 21:10:05 UTC, Phil wrote:
Hi, I'm new to D and having a go at writing some image
processing stuff using Vladimir's ae.graphics library.
To filter (i.e. perform correlations/convolutions) on a view
with colour type C, I'd like to perform intermediate
calculations using a colour with the same number of channels as
C, but all of type double, and then to convert back to
something of type C at the end.
e.g. for a horizontal blur I'd like to keep a running total per
channel, packaged in an all-doubles colour type, and then write
(total / kernel width) for each channel back into a value of
type C.
How do I perform the necessary type magic here? Thanks
Hi Phil,
The Color template implements opCast for types with the same set
of fields, so you should be able to just cast a struct with ubyte
fields to one with double fields (or use std.conv.to). The only
restriction is that the fields must have the same order.
You can use the ChangeChannelType template to create a Color type
from an existing one but a different type for the channel fields,
for example this assert will hold:
static assert(is(ChangeChannelType!(RGB, ushort) == RGB16));
To create a view with double-typed channels from an RGB view, you
can use colorMap:
alias doubleTypedView = colorMap!(c =>
cast(ChangeChannelType!(typeof(c), double))c);
You can use this as with any other view transform:
auto i = onePixel(L8(1));
auto d = i.doubleTypedView();
assert(d[0, 0].l == 1.0);
By the way, as I've never tried using floating-point types, the
code didn't quite work with them as it is, as some templates
expected integral types in a few places. I guess you've fixed
things on your side? Anyhow, I've now pushed a commit which fixes
and adds tests for FP types.
