Re: How to draw a bitmap with Alpha values preserved in CGContext?

• Subject: Re: How to draw a bitmap with Alpha values preserved in CGContext?
• From: Marc Van Olmen <email@hidden>
• Date: Thu, 29 Jun 2006 08:49:55 -0400
• Delivered-to: email@hidden
• Delivered-to: email@hidden

I just noticed that the technical note:

<http://developer.apple.com/technotes/tn2005/tn2140.html>

saids that

?????

thx for any clue?

marc

On 28 Jun 2006, at 20:20, Marc Van Olmen wrote:

Noticed mistake

G was mentioned twice second G need to be B of course...

On 28 Jun 2006, at 20:18, Marc Van Olmen wrote:

The same as provided CGDraw sample code by apple

CGBitmapContext is typical 8-bit ARGB bitmap.

when I draw the CGImageRef (obtained by QT GraphicsImporter or by CGImageSource...) with CGContextDrawImage and I look with the debugger (and also onscreen) the values of each pixel are the following

R(cg)= R*A,
G(cg)= G*A,
G(cg)= G*A
A(cg)=A

I don't want that I want to obtain

R(cg)= R,
G(cg)= G,
G(cg)= G
A(cg)=A

I know how to do this with QT not sure how to do this with.... CG

thx,

marc

On 28 Jun 2006, at 19:30, Shawn Erickson wrote:

On 6/28/06, Marc Van Olmen <email@hidden> wrote:

Is there away to fix this with CG?

I think you need to better explain the issue and exactly what you are
trying to achieve before folks can help much.

First what type of CGContext are you attempting to draw into? What is
the source for the image you are drawing? etc.

-Shawn

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