On 6/4/2012 6:48 AM, Miles Fidelman wrote:
BGB wrote:
and, recently devised a hack for creating "component layered JPEG
images", or, basically, a hack to allow creating JPEGs which also
contained alpha-blending, normal maps, specular maps, and luma maps
(as an essentially 16-component JPEG image composed of multiple
component layers, with individual JPEG images placed end-to-end with
marker tags between them to mark each layer).
dunno if anyone would find any of this all that interesting though.
well, I'd certainly be interested in seeing that hack!
Mile Fidelman
from a comment in my JPEG code:
<--
BGB Extensions:
APP11: BGBTech Tag
ASCIZ TagName
Tag-specific data until next marker.
"AlphaColor":
AlphaColor
RGBA as string ("red green blue alpha").
APP11 markers may indicate component layer:
FF,APP11,"CompLayer\0", <layername:ASCIZ>
"RGB": Base RGB
"XYZ": Normal XYZ (XZY ordering)
"SpRGB": Specular RGB
"DASe": Depth, Alpha, Specular-Exponent
"LuRGB": Luma RGB
"Alpha": Mono alpha layer
Component Layouts:
3 component: (no marker, RGB)
4 component: RGB+Alpha
7 component: RGB+Alpha+LuRGB
8 component: RGB+XYZ+DASe
12 component: RGB+XYZ+SpRGB+DASe
16 component: RGB+XYZ+SpRGB+DASe+LuRGB
-->
"AlphaColor" was an prior extension, basically for in-image chroma-keys.
the RGB color specifies the color to be matched, and A specifies how
"strongly" the color is matched (IIRC, it is the "distance" to Alpha=128
or so).
it was imagined that this could be calculated dynamically per-image, but
doing so is costly, so typically a fixed color is specified during
encoding (such as cyan or magenta).
"CompLayer" is the component layers.
currently, this tag precedes the SOI tages.
example:
FF,APP11, "CompLayer\0", "RGB\0"
FF,SOI
...
FF,EOI
FF,APP11, "CompLayer\0", "XYZ\0"
FF,SOI
...
FF,EOI
...
basically:
most component-layers are generic 4:2:0 RGB/YUV layers (except the mono
alpha layer, which is monochrome).
the layers may share the same Huffman and Quantization tables (by having
only the first layer encode them).
the RGB layer always comes first, so a decoder that doesn't know of the
extension, will just see the basic RGB components. also all layers are
the same resolution.
this is hardly an "ideal" design, but was intended more to allow a
simple encoder/decoder tweak to handle it (currently, it is
encoded/decoded by a function which may accept 4 RGBA buffers, and may
shuffle things around slightly to encode them into the layers).
the in-program layers are:
RGBA;
XYZD ('D' may be used for parallax mapping, and represents the relative
depth of the pixel);
Specular (RGBe), this basically gives the reflection color and shininess
of surface pixels;
Luma (RGBA).
so, yes, it is all a bit of a hack...
there was also a little fudging to the my AVI code to allow these videos
to be used for surface video-mapping (basically, the video is streamed
into all 4 layers at the same time).
example use-cases of something like this would likely be things like
making animated textures which resemble moving parts (such as metal
gears and blinking lights), or alternatively as a partial alternative to
using 3D modeled character faces (the face moving is really the texture
and animation frames, rather than 3D geometry), however presently this
is likely a better fit for animated textures than for video-maps.
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