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Date Posted: 07:34:56 06/27/01 Wed
Author: Michel
Subject: Re: Envision - Conversion to Black and White
In reply to: Dirk Schütze 's message, "Envision - Conversion to Black and White" on 04:24:18 06/27/01 Wed

Hi Dirk,

Envision has two methods to perform an image conversion. One is to use dithering, and the other is to let windows do the color mapping from one format to another. Windows will use thresholding, but you cannot control the threshold.

It is quite easy to do. You can create a class derived from TImageTransform, for example, TBWThresholdTransform. Then use the RGB property on every pixel to read the RGB values (for grayscale only one needs to be read, as for every pixel they are the same). From the original value you can apply your threshold.

There are examples of many transforms in EnTrans.Pas. Let me know if you have problems.

Best regards,


>When converting a greyscale image to black and white,
>is there a possibility to set a value which indicates
>whether a color will be converted to black or white?
>Example: setiing this value to 128 converts 0 - 127 to
>black and 128 - 255 to white. Or something like that...
>I think in graphic programs this is usually called
>If there is not such a property yet, can you give me a
>hint how to extend your code to get this result?
>Thanks for your help!

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