Stretching data with arcsinh method

[Sanseb]

Hey James, is there a way to create/add arcsin hyperbolic curves for Stretching Data in Affinity similar to Photoshop? It´s being said that stretching with this will preserve star size and color balance. I would like to give it a try?

See this link for further information:

https://www.cloudynights.com/topic/595610-photoshop-color-preserving-arcsinh-stretch/

 

Cheers,

 

Sebastian

[John Rostron]

The answere seems to be No. Although field expressions can use sine, cosine and their arcs, there is no hyperbolic equivalents. Neither is there an exponential or logarithmic fumction.

You might like to add a comment to my request for exponential function.

John

[Alfred]

41 minutes ago, John Rostron said:

Although field expressions can use sine, cosine and their arcs, there is no hyperbolic equivalents. Neither is there an exponential or logarithmic fumction.

If we at least had natural logs we could use the following formula:

arcsinh x = ln[x + √(x² + 1)]

 

 

 

[Lisbon]

Its been a while but i remember trying to replicate this in affinity photo. I wanted to see if this method could be useful for recovering shadows. I failed. If im not mistaken its not as simple as just applying arcsinh(x).

The original info gives some clues:

"The calculation of the curve was a very interesting problem. I eventually solved it by working backwards from the final Arcsinh curve in an iterative manner from the final point backwards - building a curve that with a double lookup matched the Arcsinh curve as closely as possible."

[Lisbon]

There is a video in Czech (i think) on youtube about this topic.
Unfortunately i dont understand a single word.

TekBo Studio: Rozšíření dynamického rozsahu pomocí Arcsinh v Affinity Photo

 

[v_kyr]

3 hours ago, Lisbon said:

There is a video in Czech (i think) on youtube about this topic.
Unfortunately i dont understand a single word.

TekBo Studio: Rozšíření dynamického rozsahu pomocí Arcsinh v Affinity Photo

Also the Youtube Video descr. references some "Arcsinh Transformation into Affinity Photo curves" values ...

arcsinh-transform.pdf

[Lisbon]

Thank you @v_kyr