# How can I improve on Image3D to produce higher resolution and better colors?

Most of the pixels in this image are black, but Image3D displays them as transparent. That's actually good for my application, but it is unexpected without an alpha channel. The main problem is getting a good rendering in 3D. In 2D, analogous images are crisp and colorful (2nd image).

I'm in Win10, mma 12, i7-4790K, 32G, NVIDIA Quadro 4000.

(* This takes 20 minutes to run *)

a = 0;
b = 0;
c = 0;
d = 0;
e = 0;
f = 0;
g = -.5;
h = 1.5;

bckx =.;
bcky =.;
bckz =.;
sum =.;

tup = tupstart = Tuples[{a, b, c, d, e, f, g, h},
3];

bckx = RandomReal[{0, 0}, {532, 532, 532, 3}];
bcky = RandomReal[{0, 0}, {532, 532, 532, 3}];
bckz = RandomReal[{0, 0}, {532, 532, 532, 3}];

For[k = 1, k <= 512, k++, bckx[[All, All, k]] = tup[[k]]];
For[j = 1, j <= 512, j++, bcky[[All, j, All]] = tup[[j]]];
For[i = 1, i <= 512, i++, bckz[[i, All, All]] = tup[[i]]];

sum = bckx + bcky + bckz;

For[i = 1, i <= 532, i++,
For[j = 1, j <= 532, j++, For[k = 1, k <= 532, k++,
If[((0 > sum[[i, j, k, 1]]) || (sum[[i, j, k, 1]] > 1) ||
(0 > sum[[i, j, k, 2]]) || (sum[[i, j, k, 2]] > 1) ||
(0 > sum[[i, j, k, 3]]) || (sum[[i, j, k, 3]] > 1)),
( sum[[i, j, k, 1]] =
sum[[i, j, k, 2]] = sum[[i, j, k, 3]] = 0)]]]];

Image3D[sum]