Creating Bitmap from byte[]

xds4lx · 01-11-2010, 05:28 PM

I cant seem to get this to work. I have a program in C++ that returns to my C# app through a DLL a char* (byte[]) on the C# side. The image data is stored as RGBA, I am trying to turn this into a bitmap, however when trying to create it from a stream i get an exception of:

Parameter is not valid.

I also tried:

Code:

Bitmap bmp = new Bitmap(width,height);

BitmapData bmpData = bmp.LockBits(new Rectangle(0,0,width,height), ImageLockMode.WriteOnly, PixelFormat.Format32bppArgb);
Marshal.Copy(imgData, 0, bmpData.Scan0, imgData.Length);
bmp.UnlockBits(bmpData);

Which sort of works however all the image colors are now way off, and I know this is due to the PixelFormat, is there no way to do this without swapping pixels in the data?

[Edit]
Well I tried swapping all the bytes from RGBA to ARGB and that just made it look even worse.

theoobe · 01-11-2010, 05:39 PM

I know you've said stream doesn't work, but maybe try this anyway? It works for me...

Code:

public static Bitmap bytes2bmp(byte[] data)
{
    return new Bitmap(new System.IO.MemoryStream(data));
}

xds4lx · 01-11-2010, 05:41 PM

That is basically what I tried, from what I understand you can only create the file from the stream if the stream has the bitmap header information in it.

xds4lx · 01-11-2010, 06:00 PM

Well I solved the problem. Even though the image was in RGBA format it was being displayed wrong, I swapped the R and B ad now the image shows up correctly, using the LockBits and UnlockBits method.

Cat · 01-15-2010, 04:03 PM

Quote:

Originally Posted by xds4lx

Well I solved the problem. Even though the image was in RGBA format it was being displayed wrong, I swapped the R and B ad now the image shows up correctly, using the LockBits and UnlockBits method.

It's probably endian issues. 32bppARGB (which is what pixel format C# is expecting) is stored as a 32 bit number with alpha in the most-significant-byte, red in the second-most-significant-byte, etc.

Now, on a big-endian machine this would be the same as the order of the bytes within the 32-bit integer, but on a little-endian machine, blue is stored and read first (at the lowest byte address), then green, red, alpha. So if you're writing bytewise, you need to write B G R A in order to read it as 32bppARGB.

01-11-2010, 05:28 PM	#1
xds4lx Registered User Join Date: Nov 2001 Posts: 626	Creating Bitmap from byte[] I cant seem to get this to work. I have a program in C++ that returns to my C# app through a DLL a char* (byte[]) on the C# side. The image data is stored as RGBA, I am trying to turn this into a bitmap, however when trying to create it from a stream i get an exception of: Parameter is not valid. I also tried: Code: Bitmap bmp = new Bitmap(width,height); BitmapData bmpData = bmp.LockBits(new Rectangle(0,0,width,height), ImageLockMode.WriteOnly, PixelFormat.Format32bppArgb); Marshal.Copy(imgData, 0, bmpData.Scan0, imgData.Length); bmp.UnlockBits(bmpData); Which sort of works however all the image colors are now way off, and I know this is due to the PixelFormat, is there no way to do this without swapping pixels in the data? [Edit] Well I tried swapping all the bytes from RGBA to ARGB and that just made it look even worse. __________________ "only two things are infinite, the universe and human stupidity, and im not sure about the former." - albert einstein Last edited by xds4lx; 01-11-2010 at 05:34 PM.
xds4lx is offline

01-11-2010, 05:39 PM	#2
theoobe Registered User Join Date: Mar 2009 Location: england Posts: 117	I know you've said stream doesn't work, but maybe try this anyway? It works for me... Code: public static Bitmap bytes2bmp(byte[] data) { return new Bitmap(new System.IO.MemoryStream(data)); }
theoobe is offline

01-11-2010, 05:41 PM	#3
xds4lx Registered User Join Date: Nov 2001 Posts: 626	That is basically what I tried, from what I understand you can only create the file from the stream if the stream has the bitmap header information in it. __________________ "only two things are infinite, the universe and human stupidity, and im not sure about the former." - albert einstein
xds4lx is offline

01-11-2010, 06:00 PM	#4
xds4lx Registered User Join Date: Nov 2001 Posts: 626	Well I solved the problem. Even though the image was in RGBA format it was being displayed wrong, I swapped the R and B ad now the image shows up correctly, using the LockBits and UnlockBits method. __________________ "only two things are infinite, the universe and human stupidity, and im not sure about the former." - albert einstein
xds4lx is offline

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Creating ICON form BITMAP files	Uwar	Windows Programming	0	12-21-2009 05:32 AM
Profiler Valgrind	afflictedd2	C++ Programming	4	07-18-2008 09:38 AM
OpenGL -- Bitmaps	HQSneaker	Game Programming	14	09-06-2004 04:04 PM
Copying Bitmap Resources without Creating HDC's	bartybasher	Windows Programming	1	08-02-2004 06:35 AM
Help creating a Bitmap	Kristian25	Windows Programming	1	02-25-2003 05:17 AM