Check if GDI+ bitmap has transparency
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I just posted this in the VB group, but then realized that this is most likely the proper place to post my question. :) Here it goes: I have opened an image as a bitmap using GDI+. Before I save it I want to know if the image has transparency in it. That is; is there any pixels in the bitmap that has the transparent color? I have made a solution that looks like this:
Dim objImage As Drawing.Bitmap = Drawing.Image.FromFile("png_with_transparent_bg.png")
Dim booTransparentColorFound As Boolean = False
If Bitmap.IsAlphaPixelFormat(objImage.PixelFormat) Then
For y As Integer = 0 To objImage.Height - 1
If booTransparentColorFound Then Exit For
For x As Integer = 0 To objImage.Width - 1
Dim objColor As Drawing.Color = objImage.GetPixel(x, y)
If objColor.A = Color.Transparent.A And _
objColor.R = Color.Transparent.R And _
objColor.G = Color.Transparent.G And _
objColor.B = Color.Transparent.B _
Then
booTransparentColorFound = True
Exit For
End If
Next
Next
End IfThe problem is that if the image is very big, and there is no transparent pixel in it (or a transparent pixel is located in the lower right corner), the routine is very slow. Is there some quicker way to determine if there is transparency in the image? Thanks in advance. ...Allan, Denmark
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I just posted this in the VB group, but then realized that this is most likely the proper place to post my question. :) Here it goes: I have opened an image as a bitmap using GDI+. Before I save it I want to know if the image has transparency in it. That is; is there any pixels in the bitmap that has the transparent color? I have made a solution that looks like this:
Dim objImage As Drawing.Bitmap = Drawing.Image.FromFile("png_with_transparent_bg.png")
Dim booTransparentColorFound As Boolean = False
If Bitmap.IsAlphaPixelFormat(objImage.PixelFormat) Then
For y As Integer = 0 To objImage.Height - 1
If booTransparentColorFound Then Exit For
For x As Integer = 0 To objImage.Width - 1
Dim objColor As Drawing.Color = objImage.GetPixel(x, y)
If objColor.A = Color.Transparent.A And _
objColor.R = Color.Transparent.R And _
objColor.G = Color.Transparent.G And _
objColor.B = Color.Transparent.B _
Then
booTransparentColorFound = True
Exit For
End If
Next
Next
End IfThe problem is that if the image is very big, and there is no transparent pixel in it (or a transparent pixel is located in the lower right corner), the routine is very slow. Is there some quicker way to determine if there is transparency in the image? Thanks in advance. ...Allan, Denmark
There are two things you could do (first way will not speed up the processing but is just a method improvement): 1) Only need to check the alpha channel (assuming any transparent colour is counted)...
If objColor.A != 255 Then ...(As the alpha channel IS the 'trasparency' aspect of the colour, you only need to check this). 2) Lock the Bitmap and loop through the raw data (this is REALLY fast)... loads of examples on web... from msdn[^] Also... if all you want to know is if the image could contain transparency... check the PixelFormat of the bitmap for transparency. Hope this helps.Matthew Butler
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I just posted this in the VB group, but then realized that this is most likely the proper place to post my question. :) Here it goes: I have opened an image as a bitmap using GDI+. Before I save it I want to know if the image has transparency in it. That is; is there any pixels in the bitmap that has the transparent color? I have made a solution that looks like this:
Dim objImage As Drawing.Bitmap = Drawing.Image.FromFile("png_with_transparent_bg.png")
Dim booTransparentColorFound As Boolean = False
If Bitmap.IsAlphaPixelFormat(objImage.PixelFormat) Then
For y As Integer = 0 To objImage.Height - 1
If booTransparentColorFound Then Exit For
For x As Integer = 0 To objImage.Width - 1
Dim objColor As Drawing.Color = objImage.GetPixel(x, y)
If objColor.A = Color.Transparent.A And _
objColor.R = Color.Transparent.R And _
objColor.G = Color.Transparent.G And _
objColor.B = Color.Transparent.B _
Then
booTransparentColorFound = True
Exit For
End If
Next
Next
End IfThe problem is that if the image is very big, and there is no transparent pixel in it (or a transparent pixel is located in the lower right corner), the routine is very slow. Is there some quicker way to determine if there is transparency in the image? Thanks in advance. ...Allan, Denmark