Convert image data (PDEImage) in PDF to DIB using C++? - pdf

Question

I am trying to extract all the images in a PDF and then convert them into DIB format. First part is easy. I extract all the contents in the PDF, then iterate through them and whenever I find a PDEImage, I put them in an array.
But I am clueless about how to go about the second part. Looks like all the AVConversion methods allow you to convert a whole page of a PDF, not just images, into other formats.
Is there any way I can accomplish this task? Thanks in advance!
EDIT: Further elaborating the problem.
I am writing an Adobe Acrobat Plug-in using Visual C++ with .NET Framework 4.
The purpose of the plug-in is to (among other things) extract image data from a PDF file, then convert those data to DIBs. The need to convert to DISs is because I then pass those DIBs to another library which do some image correction work on them.
Now my problem is with converting the said image data in PDFs to DIBs. The image data on PDFs are found in a format called PDEImage (Ref Link) where apparently it contains all the color data of the image. Now I'm using the following code to extract the said image data bits from the image to be used with CreateCompatibleBitmap() and SetBitmapBits() to obtain a HBITMAP handle. Then, I pass that along with other necessary parameters to the GetDIBits() to obtain a DIB in the form of a byte array as stated in the MSDN.
void GetDIBImage(PDEElement element)
{
//Obtaining a PDEImage
PDEImage image;
memset(&image, 0, sizeof(PDEImage));
image = (PDEImage)element;
//Obtaining attributes (such as width, height)
//of the image for later use
PDEImageAttrs attrs;
memset(&attrs, 0, sizeof(attrs));
PDEImageGetAttrs(image, &attrs, sizeof(attrs));
//Obtainig image data from PDEImage to a byte array
ASInt32 len = PDEImageGetDataLen(image);
byte *data = (byte *)malloc(len);
PDEImageGetData(image, 0, data);
//Creating a DDB using said data
HDC hdc = CreateCompatibleDC(NULL);
HBITMAP hBmp = CreateCompatibleBitmap(hdc, attrs.width, attrs.height);
LONG bitsSet = SetBitmapBits(hBmp, len, data); //Here bitsSet gets a value of 59000 which is close to the image's actual size
//Buffer which GetDIBits() will fill with DIB data
unsigned char* buff = new unsigned char[len];
//BITMAPINFO stucture to be passed to GetDIBits()
BITMAPINFO bmpInfo;
memset(&bmpInfo, 0, sizeof(bmpInfo));
bmpInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
bmpInfo.bmiHeader.biWidth = (LONG)attrs.width;
bmpInfo.bmiHeader.biHeight = (LONG)attrs.height;
bmpInfo.bmiHeader.biPlanes = 1;
bmpInfo.bmiHeader.biBitCount = 8;
bmpInfo.bmiHeader.biCompression = BI_RGB;
bmpInfo.bmiHeader.biSizeImage = ((((bmpInfo.bmiHeader.biWidth * bmpInfo.bmiHeader.biBitCount) + 31) & ~31) >> 3) * bmpInfo.bmiHeader.biHeight;
bmpInfo.bmiHeader.biXPelsPerMeter = 0;
bmpInfo.bmiHeader.biYPelsPerMeter = 0;
bmpInfo.bmiHeader.biClrUsed = 0;
bmpInfo.bmiHeader.biClrImportant = 0;
//Callling GetDIBits()
//Here scanLines get a value of 0, while buff receives no data.
int scanLines = GetDIBits(hdc, hBmp, 0, attrs.height, &buff, &bmpInfo, DIB_RGB_COLORS);
if(scanLines > 0)
{
MessageBox(NULL, L"SUCCESS", L"Message", MB_OK);
}
else
{
MessageBox(NULL, L"FAIL", L"Message", MB_OK);
}
}
Here are my questions / concerns.
Is it correct the way I'm using CreateCompatibleDC(), CreateCompatibleBitmap() and SetBitmapBits() functions? My thinking is that I use CreateCompatibleDC() to obtain current DC, then create a DDB using CreateCompatibleBitmap() and then set the actual data to the DDB using SetBitmapBits(). Is that correct?
Is there a problem with the way I've created the BITMAPINFO structure. I am under the assumption that it need to contain all the details regarding the format of the DIB I will eventually obtain.
Why am I not getting the bitmap data as a DIB to the buff when I call GetDIBits()?

Answer 1

I do not know the library you use to access the inner structures of a PDF file but the problem at hand will have tree distinct subproblems:
Find all images in the PDF file
Decode the images to their components
Convert the decoded image to a DIB
Find all Images
Images can occur inside content streams or in streams attached to dictionaries. To find all images in content streams, you need to find all content streams in either Pages, XObjects or Patterns. Each of those can have a Resources -> XObject dictionary that references all XObjects (and an XObject can be an Image).
If you avoid the inline images you might simply scan the PDF file and each dectionary that is of type XObject subtype Image can be decoded.
Decode
All streams (inline in content streams) of in separate objects in the PDF file are encoded and mught need post processing using the Decode arrays. There are several filters that you need to be able to perform for decoding. Flate decode (ZLIB), JPEG and CCITT (fax G3/G4) are probable the most used for images. Hopefully the PDF library you use will know how to decode the streams..
Next there are Decode arrays (a bit rare) where each color component can be scaled from an input value to an output value. This is a linear transformation.
To DIB
Next in line is the conversion of the decoded image to a DIB. This means you need to convert the color components to something Windows can 'get' (eg, Palette, grayscale (special palette) of RGB. PDF supports a very very large variety of color spaces and converting them to RGB is no sinecure. You best hope here is that the PDFs you need to process only use a select subset (like RGB and palette). Now a DIB can be simply created by creating the bitmap header (BITMAPINFO), fill in all data and call the DIB creation function CreateDIBSection and them process the DIB the way you application needs.
Epilogue
All in all: to be able to process all PDF files and find all images is quite a daunting task, if you control the source if teh PDFs and you know they are always in DeviceRGB format and always JPEG etc and never inlined into the content stream it is do-able.