I’ve touched on the idea of tonal crush in a few posts here and there, but it occurs to me that I’ve never stopped to fully explain the concept – or its implications for modeling.
Time to fix that!
A Brief Explanation
Tonal crush is, at its most basic, the apparent loss of tonal variation within a certain color, when placed alongside contrasting colors. The tones are literally crushed together, so that a color looks more monochromatic.
To explain why this happens, it helps to come in through a side entrance.
High Dynamic Range
A few years ago, High Dynamic Range – or HDR – processing became something of a rage. Nowadays its gone thoroughly mainstream, and even pops up in phone cameras, but I find that few people are aware of the principles that underpin HDR processing.
Simply put, there is a thing called dynamic range. Dynamic range refers to the range of brightness that a sensor can “see”. The human eye, as a sensor, can see about twenty or so “stops” – changes in brightness – at a time. We’re amazingly good at being able to discern details in areas of brightness and areas of shadow simultaneously.
Camera sensors, on the other hand, see far fewer stops. About half as many. This is why it’s difficult to capture photos that mimic what we see. If you’ve ever shot a picture with a perfectly exposed landscape and a white, overexposed sky, you’ve found the limitations in your camera’s dynamic range. If you’ve ever taken a portrait only to have your subject backlit against a blue sky, you’ve also found the limitations in your camera’s dynamic range.
That’s where HDR comes in. It’s a processing trick that combines several images of different exposures to create a final image with a far higher dynamic range than the camera could capture on its own. Here is a good example of HDR in action:
What you see here are the three original images that were combined through HDR processing into the final composite image. An image that comes closer to what our eyes really see. You can find more examples HERE.
And This Relates to Color How?
Okay. So a camera sensor can only “see” a certain range of brightness. The rest gets “crushed” into either highlight or shadow.
Something similar happens with color…but I’ve found it’s something the human eye is susceptible to, as well. Consider a single color that you’ve put a lot of shading effort into. It’s got a lot of rich tonal variation going on. Like so:
That may be green, but it’s green with character, damnit. It’s green that has lived a life.
But when highly contrasting colors next to it, something happens.
Now the camera (and your eyes, too), has to ingest a much bigger range of color information. There’s green. But there’s also white and those vibrant reds. The contrast “crushes” the tonal variation in the green, making it look monochrome.
With the Ki-84 above, it took several weathering tricks to bring it back…accentuating the tones in the green, breaking up the surface with panel line accents, and toning down the hinomarus and home defense squares.
But this tonal crush is something to watch out for on any project with highly contrasting colors.
Like this Bf 109:
And this Fiat G.55:
So How Do You Fight “Tonal Crush”?
As GI Joe cartoons taught me growing up, knowing is half the battle.
Seriously. Just knowing the color scheme you’re going for before you start throwing paint around, and adapting in advance, is going to make a huge difference. If you’re going to have a busy, contrasty camo scheme going on, consider being more exaggerated with the shading and variation. Consider mixing a blend of the camo colors and spraying it on top of everything as a very light filter, since tying the colors together, even slightly, will help reduce tonal crush.
Case in point – I knew going in that my French P-47 would be facing tonal crush from the red cowl, yellow bands and French roundels. So I put extra effort varying up the Olive Drab…and it maintained its filthiness out the other side.
If you’re facing off against high-viz markings, like say a US Navy jet from the 1960s, take that into account. If your gull gray and white look just a bit too dirty before you place the decals, it should look just right once the color party comes to visit.
On the flip side, if you’re doing low-visibility gray, there’s really no tonal crush to worry about, so any shading and tonal work you do will show up rather well.
Case in point, my recently wrapped A-4F Skyhawk:
In the end, this is just a little minor side curiosity of modeling – but I hope a few find it useful.