Colour operations using CyberShadow's graphics library

[Vladimir Panteleev via Digitalmars-d-learn]

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.