Starting with version 2.0, Filter Forge officially supports high dynamic range (HDR) colors across its entire rendering pipeline, from input images through components to rendered results.
In the example below, we load Paul Debevec’s famous "Grace Cathedral" HDRI probe and increase its brightness (by adding a bright color to it via the Linear Dodge blending mode) so that it becomes greater than 1 in some areas, then we blur it, and finally we decrease the brightness back to the original level. If we fed this example into our old LDR pipeline, it would clip the colors exceeding the maximum value (you’d see flat gray spots in the rightmost preview), but our new HDR pipeline handles overbright colors perfectly well – as evidenced by this screenshot:
But why do we need HDR in Filter Forge?
Of course, for making fire! Creating flaming-hot stuff is a lot easier when you’re not confined within the limited color range:
And the starfields, the starfields!
And of course, how could we forget explosions!
HDR-Compatible Components
Over 60% of components in Filter Forge 2.0 have been rewritten to support HDR colors. Many familiar operations, like Blur, High Pass , Blend, Levels and Perlin Noise and many more are now able to natively handle HDR colors where RGB values can range from zero to basically infinity.
HDR Color Picker
When you turn the new HDR checkbox on, the Color Picker lets you enter RGB colors with unlimited channel values. From now on, you are free to use colors as bright and vibrant as you want – the Sun’s the limit!
But there’s more – we went beyond HDR. In addition to normal HDR colors, Filter Forge now supports HDR colors with negative RGB values. You can even create mixed-sign HDR colors which can have both positive and negative RGB channels:
Despite all these additions, the new Color Picker retains the simplicity, responsiveness and ease of use of its previous version, so you won’t have to change your color-picking habits.
Displaying Impossible Colors
Thankfully, modern monitors can’t display HDR colors – we’d rather prefer our retinas not burned out due to some dude’s urge to simulate a realistic Sun in a Filter Forge filter. But anyway, how can one visualize solid colors brighter than 1 or darker than 0, especially considering the fact that the latter is physically impossible? Here’s our answer – look at the color swatches:
- Positive HDR colors, i.e. colors that have at least one color channel greater than 1 and no negative channels, are denoted as HDR+ and visualized with a white-hot spot in the center. The edges of the swatch show the normalized LDR version of the color to give you an idea about its hue and saturation, and the perceived ‘hotness’ of the middle area of the swatch gives you an idea about the brightness.
- Negative HDR colors, that is, colors where all RGB channels are negative, are denoted as HDR- and displayed with a black spot in the middle. As with the HDR+, the edges give you an idea about ‘hue’ and ‘saturation’, and the width of the dark middle area about the ‘brightness’.
- Mixed-sign colors (those that have both positive and negative RGB channels) are denoted as HDR± and are shown with a gray area in the middle. As with HDR+ and HDR-, the higher the RGB values get, the wider the middle becomes.
Old Components Learn New Tricks
Unexpectedly even for us developers, high dynamic range colors turned out to be surpisingly useful for enriching the look of old tired components. Just compare how more vibrant they look with the new HDR colors:
Let Us Know What We’re Missing!
We added the HDR support to Filter Forge because of its enormous creative and computational benefits, but we didn’t aim at HDR artists in particular. However, we are open to any ideas and suggestions how to make our HDR functionality more well-rounded – perhaps we’re just missing a few touches here and there. Tonemapping, inspectors, fullstops, exposures, whatever – let us know what we’re missing!
