Transparent Image?

Question

User-370989946 posted

I'm trying to draw a totally transparent image - 200 pixels wide and 500 pixels high - all I get is a black image.

Dim ChartBitMap As Bitmap = New Bitmap(ChartWidth, ChartHeight)Dim ChartGraphics As Graphics = Graphics.FromImage(ChartBitMap)

ChartGraphics.Clear(Color.Transparent)

ChartBitMap.Save("C://Test_transparent.gif", System.Drawing.Imaging.ImageFormat.Gif)

Thanks,

Gretchen

Answer 1

User1080017370 posted

Have a look at http://www.bobpowell.net/giftransparency.htm, where you'll find an explanation of how to do it.

Answer 2

User-370989946 posted

Hi Robert!

Thanks for the link - I already had tried to wade through that - but there must be an easier way - All I want is a brand new totally transparent gif of a specific size. I am not trying to change an existing file. This can't be but a few lines of code. I'm obviously new to GDI+, but why doesn't graphics.clear(color.transparent) work as expected?

Thanks,

Gretchen

Answer 3

User294545519 posted

Hi Gretchen,

I believe when you do graphics.clear() you are essentially adding a new 'layer' to the image on top of the existing layers. So by adding graphics.clear(color.transparent) its as if its adding a transparent later on top. If you replace transparent with red i believe that will be added on top. So this is why its probably not working how you would expect. 

Answer 4

User-370989946 posted

Thanks Curt - that makes sense. Does this mean there is no way to 'easily' produce a transparent gif?

 

Answer 5

User1813517338 posted

I think what you have will work fine, just make the follwing change:

Change this: Dim ChartBitMap As Bitmap = New Bitmap(ChartWidth, ChartHeight)  

TO: Dim ChartBitMap As Bitmap = New Bitmap(ChartWidth, ChartHeight, PixelFormat.Format32bppArgb)