Name: alphaData

Type: property

Syntax: set the alphaData of <image> to <binaryData> 

Summary: Specifies the <binary file|binary data> that makes up the <alpha channel> of the picture in an <image> object.

Associations: image

Introduced: 1.1

OS: mac,windows,linux,ios,android

Platforms: desktop,server,web,mobile

Example:
set the alphaData of image "Hellacious" to savedAlphaChannel

Example:
if charToNum(char x of the alphaData of image 1) is 255 then next repeat

Value: The <alphaData> of an <image> consists of a sequence of <binary> values.

Description:
Use the <alphaData> <property> to control the transparency of the <pixels> in an <image>.

Each pixel is represented by 8 bits (1 byte) of alpha channel data, with pixels numbered from the top left corner of the image, left to right, then top to bottom.

A value of zero means the pixel is fully transparent; a value of 255 is fully opaque; and values in between indicate a level of partial translucency.

>*Important:*  Since the <alphaData> of an <image> is <binary file|binary data> rather than text, trying to display the data in a <field> may cause unexpected behavior.

Since each pixel is represented by 8 bits (1 byte or 1 character), you can obtain the numeric value for a given pixel using the charToNum <function>. For example, the numeric value of the <alphaData> for the tenth <pixel> is given by the <expression> charToNum(char 10 of the alphaData of <image>).

>*Important:*  When changing the <alphaData> property, make sure the new data is the correct size: 1 byte per pixel in the image. If you set an image's <alphaData> property to data whose total length is incorrect, the <a/>image appearance may be distorted.

References: maskData (property), blendLevel (property), pixels (property), imageData (property), field (keyword), image (keyword), function (control_st), property (glossary), binary file (glossary), pixel (glossary), expression (glossary), binary (glossary), alpha channel (glossary)

Tags: multimedia
