How can I make an image transparent on Android?

android:alpha does this in XML:

<ImageView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:src="@drawable/blah"
    android:alpha=".75"/>

Try this:

ImageView myImage = (ImageView) findViewById(R.id.myImage);
myImage.setAlpha(127); //value: [0-255]. Where 0 is fully transparent and 255 is fully opaque.

Note: setAlpha(int) is deprecated in favor of setAlpha(float) where 0 is fully transparent and 1 is fully opaque. Use it like: myImage.setAlpha(0.5f)

Set an id attribute on the ImageView:

<ImageView android:id="@+id/myImage"

In your code where you wish to hide the image, you'll need the following code.

First, you'll need a reference to the ImageView:

ImageView myImage = (ImageView) findViewById(R.id.myImage);

Then, set Visibility to GONE:

myImage.setVisibility(View.GONE);

If you want to have code elsewhere that makes it visible again, just set it to Visible the same way:

myImage.setVisibility(View.VISIBLE);

If you mean "fully transparent", the above code works. If you mean "partially transparent", use the following method:

int alphaAmount = 128; // Some value 0-255 where 0 is fully transparent and 255 is fully opaque
myImage.setAlpha(alphaAmount);