# What is the different between ESM and CESM?

Hello! You can see the functions used to compute ESM and CESM in `shadowsFragmentFunctions.fx`:

• ESM : `float esm = 1.0 - clamp(exp(min(87., depthScale * shadowPixelDepth)) * shadowMapSample, 0., 1. - darkness);`
• CESM: `float esm = clamp(exp(min(87., -depthScale * (shadowPixelDepth - shadowMapSample))), darkness, 1.);`

They look pretty similar to one another at a glance, but once you plot the values according to the `shadowMapSample` value, they look pretty different (for simplicity, I substituted `depthScale` and `shadowPixelDepth` for 1.0, and `darkness` for 0.0):

ESM is f1, CESM is f2. The link to the plots is here: Graphtoy

@sebavan can complement with anything I missed 5 Likes

I’m a little confused.
ESM core formula： But we use this formula:
ESM : `float esm = 1.0 - clamp(exp(min(87., depthScale * shadowPixelDepth)) * shadowMapSample, 0., 1. - darkness);`
It make the shadowMapSample without exp.Why can we omit the exponent calculation?

Seb will be the best person to answer but he’s out of office for a few days so he may take a bit to respond 1 Like

Okay~Thanks!

1 Like

No, the `shadowMapSample` is generated with the `exp`, see:

As explained in this thread, we are doing `e^(-c*(z-d))` and not `e^(-c*(d-z))`, that’s why we need to do `visibility=1-e^(-c*(z-d))` in the end.

If you want to use the formula from the original paper (which are the ones you quote), you should use CESM and not ESM in Babylon.js.

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