Shaded Options

Under the icon which allows selection of the various shading types is the command for setting shaded Options.... The various settings for Options... are Display Quality, Dithering, Pixel Grid, Depth Cueing [sic], Anti-Aliasing, Outline, Shadows and Reflections.

Some of these characteristics will only work with Shaded Software and some will only work with Ray Tracing. A table describing this follows:

Before getting into the specifics of the various options, it is appropriate at this time to discuss the use of the term Ray Tracing by I-DEAS. Ray Tracing as used by I-DEAS is a misnomer. A more appropriate term would be "Advanced Display" and it was, in fact, called just that in pre-Master Series versions of I-DEAS. Ray tracing technology revolves around the more advanced display types which require the following of light rays in a scene to determine issues associated with shadows and reflections. Indeed, in I-DEAS the only time ray tracing is actually being used is when Shadows and/or Reflections are activated.

That does not mean, however, that invoking the Ray Tracing command without Shadows and Reflections activated doesn't result in a better display. Ray Tracing uses a more advance display model even when not using ray tracing technologies. This is being discussed at this point in the document because Display Quality has a much more significant impact on the display if Shaded Software is used, although it does have some effect even with Ray Tracing.

Display Quality

Display Quality is related to some "background" computations which are a part of all displays in I~DEAS except for Shaded NURBS. These "background" computations are the effort which is being performed to turn curves and surfaces into linear approximations. This process is called tessellation. The more the tessellation, the better the display, but also the slower the display. The following are four pictures rendered with Shaded Software (so the effect of the Display Quality is more evident) using the four values of Display Quality, namely Quick, Coarse, Normal and Fine where Normal is the I-DEAS default. Display Quality is related to some "background" computations which are a part of all displays in I~DEAS except for Shaded NURBS. These "background" computations are the effort which is being performed to turn curves and surfaces into linear approximations. This process is called tessellation. The more the tessellation, the better the display, but also the slower the display. The following are four pictures rendered with Shaded Software (so the effect of the Display Quality is more evident) using the four values of Display Quality, namely Quick, Coarse, Normal and Fine where Normal is the I-DEAS default.

Compare these four pictures to the following four pictures which have the same four Display Quality settings, however, were created using Ray Tracing:

The first four pictures which are rendered with Shaded Software show a "rugged" boundary for the sphere and also show what almost look like light colored "seams" on the face of the sphere. The "rugged" boundary and the "seams" are the edges of the tessellations which were created for the display. As the Display Quality gets more refined (Quick to Coarse to Normal to Fine) the boundary gets less "rugged", moving more toward a circular outline and the "seams" get less prominent. The specularity on the surface of the sphere becomes more "focused".

The second four, created with Ray Tracing, show the same "rugged" boundary, but the surface of the sphere is just as well rendered in Quick as it is in Fine. This helps highlight the primary difference between the display model for Shaded Software and the display model for Ray Tracing which has nothing to do with ray tracing technology. In Shaded Software, the display model is calculated just at the vertices of the tessellations. The display of the interior of each polygon of the tessellation is based on an interpolation of what was computed at the vertices. This saves significant time in calculation, but reduces the quality of the overall image. Smoothing becomes much more of a "linear" process and it shows in the quality of the display.

Ray Tracing does not use this shortcut. It computes the display model for every pixel on the screen. This means that the smoothing that is done, even though it is based on a linear approximation of the geometry, is much more appropriate for the underlying surface. The user pays for the higher performance image with much slower time to display. Smoothing of the display is only accomplished from polygon-to-polygon and within polygons. That is why the edge is still "rugged" in the Ray Tracing example as well, since it is still limited by the geometry of the polygons. The difference between vertex calculation and every-pixel calculation is the primary difference between Shaded Software and Ray Tracing and as stated before, that has nothing to do with ray tracing as a technology.

Dithering

Dithering is a computational process which gives the impression of more colors being rendered than are actually supported by the graphics device. Return, for a moment, to the days when there were just eight color graphics devices. What did this mean? It meant that there were two shades of red (100% red and 0% red), two shades of green (100 % green and 0% green) and two shades of blue (100% blue and 0% blue). In order to achieve some mid-level of green, for instance, carefully placing 100% green pixels next to 0% green pixels can achieve the look of another shade of green. The patterns which are used can make the appearance of many different shades of green even though only two can be made by the graphics device. Dithering is a computational process which gives the impression of more colors being rendered than are actually supported by the graphics device. Return, for a moment, to the days when there were just eight color graphics devices. What did this mean? It meant that there were two shades of red (100% red and 0% red), two shades of green (100 % green and 0% green) and two shades of blue (100% blue and 0% blue). In order to achieve some mid-level of green, for instance, carefully placing 100% green pixels next to 0% green pixels can achieve the look of another shade of green. The patterns which are used can make the appearance of many different shades of green even though only two can be made by the graphics device.

I-DEAS is a 24-bit graphics system, which means that it can specify colors to the extent that it has 256 shades of red, 256 shades of green and 256 shades of blue. Any graphics device which supports this level of 24-bit color, does not need to have intermediate shades of color dithered into being; the shade will exist as a native shade of the graphics device. Dithering can be set to Good, Better and Best with the default being Best. The real difference is in the level of computation to achieve a successively better rendering of multiple shades of color. Again, this has no impact on a 24-bit graphics device.

Pixel Grid

Pixel Grid is a time saving device for rendering Ray Tracing images. The default value for Pixel Grid (Regular (2)) is not what the user should use for creating a final rendered picture. The advanced displays that are possible from the various settings of Ray Tracing can be very time consuming images to create. Because there are many settings to be manipulated, there can be many renderings computed before the user achieves the desired effect. In order to reduce the time necessary to get to that final rendering without compromising all the settings, Pixel Grid can be used to make a more coarse "advanced" rendering in a significantly smaller period of time. In effect, the numeric value for Pixel Grid identifies that each "n" by "n" group of pixels (where "n" is the Pixel Grid value), will be computed as if it were one pixel and that "grid" of pixels will be displayed as one computed color. There are four predefined settings, i. e., High Resolution(1), Regular(2), Coarse Image(6) and Lighting Check(10), or the user can set any integer value that he/she wishes. The following pictures are the four preset values illustrated: Pixel Grid is a time saving device for rendering Ray Tracing images. The default value for Pixel Grid (Regular (2)) is not what the user should use for creating a final rendered picture. The advanced displays that are possible from the various settings of Ray Tracing can be very time consuming images to create. Because there are many settings to be manipulated, there can be many renderings computed before the user achieves the desired effect. In order to reduce the time necessary to get to that final rendering without compromising all the settings, Pixel Grid can be used to make a more coarse "advanced" rendering in a significantly smaller period of time. In effect, the numeric value for Pixel Grid identifies that each "n" by "n" group of pixels (where "n" is the Pixel Grid value), will be computed as if it were one pixel and that "grid" of pixels will be displayed as one computed color. There are four predefined settings, i. e., High Resolution(1), Regular(2), Coarse Image(6) and Lighting Check(10), or the user can set any integer value that he/she wishes. The following pictures are the four preset values illustrated:

Although the quality of the image is severely degraded from the High Resolution(1) image to the Lighting Check(10) image, realize that the Lighting Check(10) image was approximately 100 times faster to display than the High Resolution(1) image since the Pixel Grid has an inverse-square relationship to the number of pixels in the grid (a 10 by 10 grid is being computed as if it were 1 pixel, therefore there is 100 times less information to compute).

Depth Cueing

Depth Cueing is a computation which makes geometry farther from the viewer rendered darker simply because that geometry is farther away. This is not the same as the inverse-square rule for light intensity diminishing. This is an additional "darkness" applied to how bright the image is displayed based on the additional information that the geometry is farther away from the viewer. Depth Cueing is a computation which makes geometry farther from the viewer rendered darker simply because that geometry is farther away. This is not the same as the inverse-square rule for light intensity diminishing. This is an additional "darkness" applied to how bright the image is displayed based on the additional information that the geometry is farther away from the viewer.

There is a % decay associated with this calculation which is controlled by the user. The following is how I understand this quantity is to be interpreted, however, I-DEAS does not follow this explanation during display, so there is either a bug in the software or there is an error in my understanding of the meaning (I think it is the former). Consider the following illustration:

In front of the clipping plane, 100% of the image that is computed using the display model should be displayed. Behind the rear clipping plane the image should be darkened by the % decay, i. e., the actual displayed image should be 100% of the image calculated without depth cuing considerations minus the % decay that has been requested. This should mean that 0% % decay is equivalent to no Depth Cuing at all and 100% % decay should cause everything to be black behind the rear clipping plane. If the % decay were set to 50%, then the image behind the rear clipping plane should be 50% of the image that would have been calculated without Depth Cuing. The amount of darkening that is applied between the front clipping plane and the rear clipping plane is a linear interpolation between the values computed at these planes. Again, I-DEAS does not follow this "rule", so trial-and-error is the only method of investigating Depth Cuing. In the following examples, the clipping planes are placed just in front of and just behind the geometry. The displays represent (1) no Depth Cuing, (2) Depth Cuing with % decay set to 0%, (3) Depth Cuing with % decay set to 50% and (4) Depth Cueing with % decay set to 100%.

Anti-Aliasing

First of all, Anti-Aliasing is not obvious in the Options... form. It is a pull-down next to the words Curve Smoothing. Curve Smoothing is independent of Anti-Aliasing, but the way it appears on the form, one would believe that the pull-down is in reference to Curve Smoothing. Indeed, there are no words on the form which highlight that the pull-down is for Anti-Aliasing.

Anti-Aliasing is a technique for making the boundaries between different colored surfaces seem like a smoother boundary. The issue of interest is shown in the following illustration of the display of two blocks, one red and one green. The area which is highlighted will be studied in successive illustrations in much greater detail (the area noted).

The line of demarcation or the boundary between where the red surface is displayed and the green surface is displayed can become very jagged because the pixels are of significant enough size to make the boundary an important element of display quality.

Anti-Aliasing is an attempt to eliminate the "jaggies" by fooling the eye. This is done by using at the boundary of the two surfaces colors combinations of the colors of the two surfaces. This can be illustrated by using the Pixel Grid capability of Ray Tracing display. In the following display, we see a Pixel Grid of 32, which means that each 32-by-32 "clump" of pixels will be computed as if they were one pixel. This will make pixels at the boundary very large and easy to see. In this display we are seeing how Shaded Software handles this color boundary. (Shading Type was changed to No_Shading so that "pure color" could be studied. Also, this display cannot be directly made because Pixel Grid can only be used with Ray Tracing and Ray Tracing always uses some Anti-Aliasing. The picture to follow was "manufactured" from a Ray Tracing image but accurately communicates what would happen in a Shaded Software display.)

It is obvious that nothing is being done with colors at the boundary except deciding whether the pixel should be red or green. This will create a very jagged line between the red and green surfaces. This is the "jaggies" to which reference was made above.

The following pictures show this same 32-by-32 Pixel Grid displayed for the three possible Anti-Aliasing settings, namely, Good, Better and Best. Each of these levels of Anti-Aliasing show that at the boundary some of the pixels are a mixture of red and green in different quantities. On first inspection, it would appear that such use of color is of no value, but the eye is easily fooled. Consider the analog of the newspaper picture. If you look closely at the picture, it is nothing but different size dots. However, pull back from the "dots" and our eye sees a picture. A similar occurrence happens with the mixed-colored pixels at the boundary of the two surfaces.

In the following four images, we will see the boundary of the two surfaces rendered at a Pixel Grid of 1. The first is Shaded Software, where no Anti-Aliasing is happening, followed by Good Anti-Aliasing, Better Anti-Aliasing and Best Anti-Aliasing. I leave it to the viewer to decide which is the best image. Just remember, Anti-Aliasing computation can be expensive.

Outline

Outline is simply the ability to put a user selected Software Hidden display on top of the Shaded Software display. It does not work with Ray Tracing display. The following are examples with and without Outline displays. Outline is simply the ability to put a user selected Software Hidden display on top of the Shaded Software display. It does not work with Ray Tracing display. The following are examples with and without Outline displays.

Shadows

There is nothing mysterious about Shadows other than invoking them also invokes true ray tracing. Shadows are either on or off as in the following examples:

Reflections

Reflections, too, are not very mysterious. They are either on or off, however, there is a number which controls how many reflections should be calculated. This deals with how many reflections of reflections should be computed. The maximum number possible is 9. Increasing the number of Reflections to compute can significantly lengthen the time to display. Reflections cannot be activated without Shadows also being activated. Shadows can be activated without activating Reflections. The following pictures show no Reflections, 1 Reflection, 2 Reflections, 4 Reflections and 9 Reflections:Reflections, too, are not very mysterious. They are either on or off, however, there is a number which controls how many reflections should be calculated. This deals with how many reflections of reflections should be computed. The maximum number possible is 9. Increasing the number of Reflections to compute can significantly lengthen the time to display. Reflections cannot be activated without Shadows also being activated. Shadows can be activated without activating Reflections. The following pictures show no Reflections, 1 Reflection, 2 Reflections, 4 Reflections and 9 Reflections:

The viewer can determine for himself/herself which level of computation is worth waiting for in display.

Again, the I-DEAS representation of light passing through an object (I-DEAS Translucency) is not representing the true physics of the situation. Care must be exercised when trying to mix Translucency with Reflections. The result can be dramatic, but confusing.

There is an aspect of Reflection which is not working properly in Master Series. The following is the "sphere cube" repeated, but with Reflections activated with 1 Reflection computed.

The following is a similar picture that was the "slice" through the "sphere cube".

Notice that although the specularity (the white "dot" representing the light source acting specularly on the spherical surface) gets more and more "focused" as the Glossiness and the Brightness increase, the Reflections are the same level of "focus" regardless of the Glossiness and Brightness. If Glossiness and Brightness are intended to represent the "smoothness" of the surface, then the Reflections should mimic the specularity in its "focus" with changes in Glossiness and Brightness. You might also notice that Brightness of 50% is a "hard demarcation" between getting reflections and not getting reflections. None of this is true in the real-world and none of this should be true in the I-DEAS display world.

In pre-Master Series versions of I-DEAS, the "focus" of the reflections followed the "focus" of the specularity with changes in Glossiness and Brightness. Also, in pre-Master Series versions the reflections became gradually and continually more apparent as Brightness varied from 0% to 100%; the reflections didn't just "appear" when Brightness became 50% or greater.