Download Dados da implementação - PUC-Rio

Computer Graphics Foundations 2010.1
first assignment
Students:
Alexandre Valdetaro - [email protected]
Gustavo Nunes – [email protected]
Professor:
Marcelo Gattass
Project Objectives:
• Visualization in the color spaces:CIE XYZ, CIE
Lab, sRGB e XYZProjected, of the following
color groups:
– Visible Colors.
– sRGB space representable colors
– Munsell
– Kodak Minilab
Implemented Software
• A software for visualization and conversion of
all the desired color groups in all of the color
spaces.
• XNA framework has been used.
• All the screenshots from the slides have been
taken from the software.
Visible Colors
• The raw data of the spectral pure colors has
been converted to CIE XYZ in two different
ways:
– Setting Y as a fixed value
– Setting Y as y*(fixed value)
*The first conversion has been called the XYZ and the second XySlashZ
Visible Colors
• With the 401 pure color points a fan
tesselation with the black and the white was
done.
Fan tesselation
Visible Colors
• With the fan tesselated mesh, a shoestring
type tesselation refined the mesh
Visible Colors
• With the densely tesselated mesh, the
conversion to other color spaces used the
formulas from:
www.brucelindbloom.com
sRGB representable colors
• A Cube mesh has been created in sRGB space,
with its vertices: (0,0,0),
(1,0,0),(0,1,0),(0,0,1),(1,1,0),(1,0,1),(0,1,1),(1,1
,1)
• The cube has been then tesselated acording to
the refine level available in the user interface
• The densely tesselated mesh has then been
converted to other color spaces using
www.brucelindbloom.com
sRGB representable colors
Simple refinement using baricentric coordinates
Munsell colors
• The raw data was a Point Cloud in CIE Lab
space.
• Only the Hull is needed to make the mesh.
• To Obtain the hull, the segment maxima
algorithm[Morovic and Luo 2000] has been
used with discretization 16x8
• The mesh produced with the hull was then
converted to other spaces using
www.brucelindbloom.com
Munsell Colors
• The point cloud and the aproximation of the
segment maxima as the wireframe mesh
Kodak Minilab
• Used the same heuristic of Munsell, except
that the color used to render each vertex of
the mesh came with the Kodak raw data in
sRGB, so the Lab position was only used for
geometry.
Kodak Minilab
• The point cloud and the aproximation of the
segment maxima as the wireframe mesh
XYZProjected
• Represents the XYZ values projected on the plane
X+Y+Z
• Widely used representation of the visible
spectre(Horseshoe)
Known Problems
• The conversion from XYZ to lab can cause artifacts if the mesh
has very thin triangles.
• Suppose one has a triangle made with the white point and to
pure color points A and B that are so close to each other that
the triangle can be considered a line(happens in the edges of
the spectrum)
• When refining the tesselation, suppose LA the line between
the white and the point A, and LB between white and point B.
• It is desired to segment these lines and triangulate them.
• For sake of clarity the LA point will be represented with an x
and LB points with an o.
Known Problems
• After segmented, the points are connected
clockwisely
Known Problems
• When converting to Lab supposing the points are so
close that LA = LB, the lines would look coarsely like
this:
XYZ
Lab
Known Problems
• When connecting the point some counter clockwise triangles
will appear.
• Ex: the triangle LA3,LB4,LA4 is clockwise in XYZ and gets
counter clockwise in Lab
Known Problems
• sRGB will have negative valors for the full
visible spectrum.
• By the formula, any value below a fixed
constant close to zero should use a linear
function.
• So negative values with module greater than
the constant should be treated not linearly
Known Problems
• The Lab values from the Kodak Minilab raw
data does not match with the sRGB values also
provided in the raw data.
Known Problems
• The segment maxima algorithm can generate artifacts
depending on the distribution of the points.
• The first image is the expected result when connecting
the points of each segment
• The second image shows a counter clockwise triangle
END