New atmosphere causes banding when combined with bloom post processing

[mramato]

We have an app that has noticeable banding artifacts after upgrading to the latest CesiumJS.

I tracked this back to having bloom enabled with a stepSize other than 1

const viewer = new Cesium.Viewer("cesiumContainer");

const bloom = viewer.scene.postProcessStages.bloom;
bloom.enabled = true;
bloom.uniforms.stepSize = 7;

// Not needed, but makes it even worse and more noticeable
viewer.scene.highDynamicRange = true;

This is also noticeable in the Post Processing Sandcastle Example: https://sandcastle.cesium.com/index.html?src=Bloom.html&label=Post%20Processing

[sanjeetsuhag]

I will take a deeper look into why this is happening, but as a first step, I noticed that the banding was visible with the older atmosphere too - past a certain stepSize. Seems like the threshold for that to visually appear is lower with the new atmosphere.

1.92	1.93

[sanjeetsuhag]

@mramato Based on the findings above, seems like the banding was always an issue, if the stepSize was large enough - however, that threshold is just lower with the new colors of the atmosphere. Would reducing the stepSize be an option for you? If not, we'll probably have to revisit the implementation of the bloom filter.

[mramato]

@sanjeetsuhag We can live with the issue for now or set step size to one. But I gree that it seems like bloom should be revisited at some point (so we should either write up a new issue or leave this open to do so).