Re: [Inkscape-user] Problem with running program

[Hedley Finger <hfinger@xxxxxxxxxxxxxxxxxx>]

To all who replied:

> I want to create a representation of the HSV cone similar to that at
> <http://en.wikipedia.org/wiki/Image:HSV_cone.png> to show how it is
> derived from the CIE 1931 chromaticity diagram
> <http://en.wikipedia.org/wiki/Image:CIExy1931.svg>.  I want all the
> labels, arrows, and the wedge cut-out in this graphic -- which is
> unfortunately a PNG and not a vector graphic -- to be removed.
>   

I did it in Gimp in the end as follows (thanks, Gimp listers):

*Create the base of the inverted HSV cone*

1    Use the ellipse selection to create a circle selection on a white 
background.  (You might want to set up guides to locate the centre of 
the circle.)

2    Click the Blend tool, set the Gradient to  Full Saturation Spectrum 
CCW, and set the Shape to Conical (asym).

3    Click the centre of the circular selection and draw a radius.  You 
now have a circle filled with a coloured cone.

4    Set the foreground colour to white.

5    Change the Gradient to  FG Colour to Transparent and Shape to 
Radial, and draw another radius.  If the perimeter is not quite 
saturated enough, copy the FG Colour to Transparent gradient and adjust 
the copy so that the transparency sets in earlier.

6    Change the proportions  so the circle becomes an ellipse, longer in 
its horizontal axis.  This is the base of the inverted cone.

7   Add an alpha channel to the ellipse layer.

8   Change the foreground colour to black, then use the Bucket Fill tool 
to change the four white corners of the ellipse to black.

9   Choose Select > By Colour, click the black,  and cut the black 
selection.

*Create the cone*

The cone will make a tangent to the ellipse a little around the bottom 
curve from the ends.  So you will first need to copy the Full Saturation 
Spectrum CCW gradient and adjust the copy's end colours to match those 
at the point of the tangents.

1   Create a new document with a square selection on a white background.

2   Change the blend tool to Gradient: Custom copy of  Full Saturation 
Spectrum CCW.

3   Drag the blend tool horizontally from the L to R side of the square.

4   Press Ctrl+a to select the entire square.

5   Click the Perspective tool.

6   Drag the bottom L and R handles to the vertical centre line, keeping 
the horizontal grid line horizontal.  You don't need to exactly place 
the L and R corners at the centre, as this is fixed later, as long as 
the general effect of the bands of colour fanning out from the point on 
the bottom edge to the full width on the top edge is achieved.

7   Set the foreground colour to black.

8   Click the Blend tool and set Gradient to FG Colour to Transparent, 
and draw from the "point" bottom edge to the centre of the full width 
top edge.

9   Click the Bezier tool and draw an inverted triangle from the top L 
corner to the bottom centre, the top R corner and close the curve.

10  Change the path to a selection and copy the selection.

11  Make a new layer under your ellipse in the first document, paste 
your inverted coloured triangle into that layer, and move it around 
until the sloping sides are tangents to the ellipse.

The colours in the inverted triangle don't quite match up with those 
along the bottom edge of the ellipse but the effect of the HSV inverted 
cone is good enough to fool a fast moving observer.

Regards,
Hedley




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