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Date Posted: 06:48:42 05/10/00 Wed
Author: Michel
Subject: Re: about Transformations...
In reply to: Plinio 's message, "about Transformations..." on 15:42:28 05/09/00 Tue


Dear Plinio,

If you look at the brightness transform, the luminosity change is straight forward,

Luminosity := Luminosity + FPercent/100.0;

In the contrast, it is,

Theta := (Luminosity-0.5)*System.Pi;

Luminosity := Luminosity +
(((((Sin(Theta)+1.0))*0.5)-Luminosity)*Sign)*0.5;

A percentage value cannot be expressed. I don't recall from which reference I got the contrast change formula.

You are correct about the Apply method in the contrast and brightness transforms. Thanks for mentionning this to me. There is a one to one mapping to each pixel, so yes, it would conserve resources to apply directly on the source image. I have added this to my work list.

To add your own transforms, the simplest and most effective approach is simply to create a new unit, and derive you transform class from an appropriate base class. You don't need any DLL, package, etc...

Best regards

Michel

> some questions:
>
> 1) Why TConstrastTranformation hasn't a Percent like
> Brightness?
>
> 2) I read in your code:
> << { by default, Apply creates a new image, invokes
> ApplyOnDest, assigns the result to DibGraphic, and
> then frees the temporary image. This method should be
> overriden when the processing may occur directly on
> the image, converving resources. } >>
>
> why in some tranformations like contrast and
> brightness did not you redefine Apply?
>
> 3) I'd like to extend the library with my own
> transformations. What's the best way? Should I create
> a DLL, a package, a library ...
>
> Thanks,
> good work.
>
> Plinio

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