Should bloom strength change for different colors of same strength?

[Denny]

Engine Version 4.3.0 Preview

OS Win 8.1 Pro

GPU GeForce GTX 770, DirectX 11, Driver 337.88

I’m making a simple flashy game and just started blocking out the basic materials to see how I should drive them for the visual results I want. Below I have my super simple material, where I multiply the color to get a stronger emissive.

Here is the result I am getting for the following colors, in a pitch black level:

• rgb(1,1,1)*3 = rgb(3,3,3) white
• rgb(1,0,0)*3 = rgb(3,0,0) red
• rgb(0,1,0)*3 = rgb(0,3,0) green
• rgb(0,0,1)*3 = rgb(0,0,3) blue
• rgb(0,1,1)*3 = rgb(0,3,3) turquoise

Note how the colors containing green blooms a lot earlier than red and blue. Below is a video showing when red and blue kicks in.

UE4 - Feedback regarding emissive

Is this related to how the engine calculates physical based materials? I expected different bloom for different colors, but with this it seems as if the bloom will come and go if I decide to dynamically switch colors during runtime.

I would like to know if I have to work around this by increasing the multiplier for some colors, or maybe there is another way to increase the bloom than this? I have used the post process volume, but it doesn’t seem to do much else than increase bloom for all equally.

Maybe the effect won’t be as noticeable when the whole level is up and running. I would like to understand how emissive colors are supposed to work, that’s all.

[Lovecraft_K]

Hi Denny -

The Bloom that emissive elements generate is a part of the post process. It is also effected by Eye Adaption (Auto Exposure). If you go into your Post Process Volume and reduce the difference between the min and max Auto Exposure you will get a more controllable bloom effect.

However, Bloom is an effect generated by a sampling of the scene using 5 different resolutions of a Gaussian Blur. So in your example it is sampling black or nothing and blurring that with you emissive colors. Since White, Turquoise and Green have a higher contrast rate with black than both Red and Blue the Bloom effect show fast at lower emissive levels. Whereas Blue which has a relatively low contrast rate with Black takes a much higher value of emissive to allow the blur effect to show color.

Hopefully that helps you out,

Thank You

Eric Ketchum

[Denny]

Thanks for the clarification Eric!

Just for future note; I had the Auto Exposure at 1.0, 1.0, 0.0 when recording the video. So it should only be the sampling that gives the current result.

[Sidonas]

What I’ve been doing is Lerping between two brightness multipliers based on the amount of green in the color plus half the red, clamped to 0-1.