Question

I am creating screenshots under Windows and using the LockBits function from GDI+ to extract the pixel data, which will then be written to a file.

To maximise performance I am also:

• Using the same PixelFormat as the source bitmap, to avoid format conversion
• Using the ImageLockModeUserInputBuf flag to extract the pixel data into a pre-allocated buffer
• This pre-allocated buffer (pointed to by BitmapData::Scan0) is part of a memory-mapped file (to avoid copying the pixel data again.)

I will also be writing the code that reads the file, so I can use (or invent) any format I wish. However I would prefer to use a well-known format that existing programs (ideally web browsers) are able to read, because that means I can visually confirm that the images are correct before writing the code for the other program (that reads the image.)

I have implemented this successfully for the PixelFormat32bppRGB format, which matches the format of a 32bpp BMP file, so if I extract the pixel data directly into the memory-mapped BMP file and prefix it with a BMP header I get a valid BMP image file that can be opened in Paint and most browsers.

Unfortunately one of the machines I am testing on returns pixels in PixelFormat64bppPARGB format (presumably this is influenced by the video adapter driver) and there is no corresponding BMP pixel format for this.

Converting to a 16, 24 or 32bpp BMP format slows the program down considerably (as well as being lossy) so I am looking for a file format that can use this pixel format without conversion, so I can extract directly into the memory-mapped file as I have done with the 32bpp format.

What raster image file formats support 48bpp (BGR order, little-endian) and/or 64bpp (BGRA order, little-endian)?

---

Edit

I have ruled out these formats so far:

• BMP: Depth limited to <=32bpp (would be a perfect match otherwise.)
• PNG: Sample order can only be RGBA.
• TIFF: Sample order can only be RGBA.

Possible partial solutions:

• OpenEXR: 48bpp only. Sample order is alphabetical by channel name; BGR fits but BGRA does not.

Answer 1

It seems that the only reason you need a standard format is for display/testing purposes. So roll your own format, but convert to PNG or TIFF for display. And then move on…life is short.