Loading an image from memory, GDI+

Question

Here's a quick and easy question: using GDI+ from C++, how would I load an image from pixel data in memory?

Answer 1

Probably not as easy as you were hoping, but you can make a BMP file in-memory with your pixel data:

If necessary, translate your pixel data into BITMAP-friendly format. If you already have, say, 24-bit RGB pixel data, it is likely that no translation is needed.

Create (in memory) a BITMAPFILEHEADER structure, followed by a BITMAPINFO structure.

Now you've got the stuff you need, you need to put it into an IStream so GDI+ can understand it. Probably the easiest (though not most performant) way to do this is to:

1. Call GlobalAlloc() with the size of the BITMAPFILEHEADER, the BITMAPINFO, and your pixel data.
2. In order, copy the BITMAPFILEHEADER, BITMAPINFO, and pixel data into the new memory (call GlobalLock to get the new memory pointer).
3. Call CreateStreamOnHGlobal() to get an IStream for your in-memory BMP.

Now, call the GDI+ Image::FromStream() method to load your image into GDI+.

Good luck!

Answer 2

There's a bitmap constructor which takes a BITMAPINFO and a pointer to pixel data directly, for example:

BITMAPINFO bmi;
memset(&bmi, 0, sizeof(bmi));
bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
bmi.bmiHeader.biWidth = 32;
bmi.bmiHeader.biHeight = 32;
bmi.bmiHeader.biPlanes = 1;
bmi.bmiHeader.biCompression = BI_RGB;
bmi.bmiHeader.biBitCount = 24;
char data[32 * 32 * 3];
// Write pixels to 'data' however you want...
Gdiplus::Bitmap* myImage = new Gdiplus::Bitmap(&bmi, data);

That's OK for an RGB image, if it's a palette image you'd need to allocate a BITMAPINFO with enough space for the RGBQUADS etc etc.

Answer 3

Use SHCreateMemStream, it takes a pointer to the data and the size of the data.

IStream *pStream = SHCreateMemStream((BYTE *) InputBuffer, Size);
// Do what you want
pStream->Release();

Answer 4

Is the "pixel data in memory" formatted as a particular image type, i.e., bitmap, TIF, PNG, etc.? If so, get it into a stream and use System.Drawing.Image.FromStream.

Answer 5

This article describes how you can load a GDI+ image from a resource (rc) file. Loading the image from memory should be similar.