R – Transparent color works on the simulator but becomes black on the iPhone

cocoa-touchimageiphonetransparency

I am trying to draw an image that has some transparent regions.
I load the image using

image = [UIImage imageNamed:@"testimage.png"];

and draw it using

[image drawAtPoint:CGPointMake(0,0)];

The UIView on which I draw the image is not opaque (and it has a transparent background color).

The problem is that everything works fine on the simulator, but when I run the app on my iPhone the transparent color becomes black! Can anyone pinpoint my error?

Best Answer

The correct answer to this problem is the .PNG format you are saving your image with. If you save as PNG-8, you will run into this problem more often that not, since it only supports 1 transparent color. If you open your .PNG file and then re-save it as a 24-bit format, you will gain genuine transparency.

Reference this thread for discussion and clarification.

EDIT: Just to be clear, .PNG does not have an 'alpha channel', so Chris' answer is misleading. Just be sure to save in 24-bit format with transparency enabled.

Related Solutions

IPhone: Layering a transparent openGL view on top of a UIView

Here's what I had to do to get this to work:

eaglLayer.opaque = NO;      
eaglLayer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:
                                kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);

And incase you're doing what I was doing and are trying to test it with the GLGravity demo, there's another call to glClearColor(0.0f, 0.0f, 0.0f, 1.0f); every time drawView is called -- so make sure you change that one to glClearColor(0.0f, 0.0f, 0.0f, 0.0f); too! :)

Ios – UIWebView background is set to Clear Color, but it is not transparent

Also set :

[webView setBackgroundColor:[UIColor clearColor]];
[webView setOpaque:NO];

Best Answer

Related Solutions

IPhone: Layering a transparent openGL view on top of a UIView

Ios – UIWebView background is set to Clear Color, but it is not transparent

Related Topic