Multicoloured radial gradient -- how to?
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.
If have tried using the clone tool to obliterate the unwanted arrows and letters, but cannot get a clean blend, not even with a blurred brush tool. One approach would be to treat a vector circle as the top of an apple pie, and create a series of wedges like slices. Then, in each wedge (slice), create a gradient from the edge to the tip. But I can't figure out how to blend adjacent wedges.
Is there another approach to get a continuous rainbow of colours around the perimeter of the circle, and then do a radial blend from white in the centre to the perimeter?
I use The Gimp for pixmaps and Inkscape for vector graphics, and also Scribus. If you don't have experience with these programs, can you describe what to do in general terms, not in specific PhotoShop, Illustrator, or InDesign terms. It shouldn't be too hard to translate a general description into the necessary actions.
Regards, Hedley
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Hedley Finger
28 Regent Street Camberwell VIC 3124 Australia Tel. +61 3 9809 1229 Fax. (call phone first) Mob. (cell) +61 412 461 558 Email. "Hedley Finger" <hfinger@...2483...>
Hedley wrote:
Is there another approach to get a continuous rainbow of colours around the perimeter of the circle, and then do a radial blend from white in the centre to the perimeter?
Inkscape, or more specifically SVG, doesn't not support conical gradients. So you would have to simulate the effect which would be messy and complicated.
If it doesn't have to be vector then do it in GIMP. On your canvas, create a circle select and fill it with the "Full saturation sectrum" gradient using the shape, "conical (asym)". Then select a white to transparent gradient and fill the same circle with the "radial" shape selected. With the circle still selected, transform (or scale) it so it's an oval. Huzaah!
If you really really want to use Inkscape, you'll need to create a very slender triangle of a certain colour then clone it so each clone is rotated by the same angle of the of the triangle, group them then add a slight blur to them. I'm not sure exacatly how it'll turn out because the outer area of the circle may not blur enough whilst the inner area will probably blur too much.
microUgly:
Is there another approach to get a continuous rainbow of colours around
the perimeter of the circle, and then do a radial blend from white in the centre to the perimeter?
If it doesn't have to be vector then do it in GIMP. On your canvas, create a circle select and fill it with the "Full saturation sectrum" gradient using the shape, "conical (asym)". Then select a white to transparent gradient and fill the same circle with the "radial" shape selected. With the circle still selected, transform (or scale) it so it's an oval. Huzaah!
Well, I got my ellipse with rainbow perimeter converging to white at the centre just great!
I want this ellipse to be the flat top of an inverted cone, with the colours on the visible "side" of the cone converging to black at the point, similar to the HSV inverted cone in http://en.wikipedia.org/wiki/Image:HSV_cone.png, but without all the labels and arrows.
Extrapolating your directions for the ellipse above, I created a rainbow gradient from one side of the ellipse to the other just fine. I created a square that has the left edge green and transforms through a number of colours to purple on the right edge.
Then I tried to squeeze the black base of the square to a point halfway from left to right on the bottom edge using the Perspective (keystone) tool. After reading section 4.8, 'Perspective", I select the entire graphic, double-click the Perspective tool, set
@ Direction (.) Normal @ Interpolation: [Cubic ] @ Clipping: [Crop to result ] @ Preview: [Image + Grid ] @ [ Number of grid lines ] [11]
Then I click on the graphic and move the bottom L handle to the middle of the bottom edge, and the bottom R handle also to the middle of the bottom edge so that there is a very short edge. The horizontal grid lines are parallel with the bottom edge. Then I click the Transform button and ... nothing happens.
So how to get the graphic to narrow from top to bottom?
Regards, Hedley
--
Hedley Finger
28 Regent Street Camberwell VIC 3124 Australia Tel. +61 3 9809 1229 Fax. (call phone first) Mob. (cell) +61 412 461 558 Email. "Hedley Finger" <hfinger@...2483...>
Hedley wrote:
So how to get the graphic to narrow from top to bottom?
Sounds to me like you might be able to use a mask or a clipping path. I've done that before with multiple grouped objects. Unfortunately masks and clips don't export nicely to PDF at the moment, but should export to a png OK.
Rygle.
Although you may be able to successively do a difference between duplicates of the cone shape and each part of the rainbow colour, and then I think you'll end up with something that will export to PDF.
rygle wrote:
Unfortunately masks and clips don't export nicely to PDF at the moment, but should export to a png OK.
On Thu, 2008-05-15 at 11:42 +1000, Hedley Finger wrote:
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.
If have tried using the clone tool to obliterate the unwanted arrows and letters, but cannot get a clean blend, not even with a blurred brush tool. One approach would be to treat a vector circle as the top of an apple pie, and create a series of wedges like slices. Then, in each wedge (slice), create a gradient from the edge to the tip. But I can't figure out how to blend adjacent wedges.
Nothing like waking up to a new challenge!
Make each wedge with a little bit larger radius than your final ellipse. Group all the wedges (Ctrl-G), go to the Fill and Stroke dialog (Shift-Ctrl-F) and use the blend slider. Add an extra ellipse with your final ellipse size. Select both the wedge group and the ellipse and use the Object->Clip->Set command to clip the group.
Is there another approach to get a continuous rainbow of colours around the perimeter of the circle, and then do a radial blend from white in the centre to the perimeter?
Try creating a new ellipse with a radial gradient from white with full opacity to white with full transparency put on top. (Don't use gradients for constructing the wedges in this case.)
To make the wedges, you can use the Tile Clones dialog to create a circle of wedges which after being grouped could be turned into an ellipse. The dialog does allow for automatically giving each wedge a different hue but I am not sure the hue shift is done properly. I've attached a quick try at using this method.
Alternatively, one could write a little perl/python script to generate each wedge with the correct color. Inkscape does support the Color Matrix filter which can rotate a hue in HSL space. It does so with a complex formula from the SVG specification.
Tav
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Tavmjong Bah