this basically is an experimental thing, i am reading a caption watermark from a BMP
image through extracting and putting together the Least Significant bits of an image.
I have created an embedder to do this, and my caption extractor is an XPCOM component.
When I extract captions from a watermarked BMP image, everything works fine. But when I
read a non-watermarked image, it causes memory leaks.
By the way, the first 32 bytes after the BMP header are used to form a 32bit integer
which tells where the offset of the last watermarked byte is.
here's the extractWatermark method, thanks.
-> johanna
/* string extractWatermark (in string url); */
NS_IMETHODIMP Extractor::ExtractWatermark(const char *url, char **_retval)
{
PRUint32 bytes, success;
PRInt32 n, compType, bmpType;
PRInt32 lastPixel, i, j, iByte, tBit, caplen, k;
char c, cBit, cByte;
char *buffer, *caption;
char *msg1 = "EX4369";
char *msg2 = "EX4353";
char *msg3 = "EX4113";
nsCOMPtr<nsIServiceManager> servMan;
nsresult rv = NS_GetServiceManager(getter_AddRefs(servMan));
if (NS_FAILED(rv)) return rv;
nsCOMPtr<nsIIOService> ioService;
rv = servMan->GetServiceByContractID(
"@mozilla.org/network/io-service;1",
NS_GET_IID(nsIIOService),
getter_AddRefs(ioService));
if(NS_FAILED(rv)) return rv;
nsCOMPtr<nsIURI> uri;
nsEmbedCString uriString(url);
rv = ioService -> NewURI(uriString, nsnull, nsnull, getter_AddRefs(uri));
if(NS_FAILED(rv)) return rv;
nsCOMPtr<nsIChannel> channel;
rv = ioService -> NewChannelFromURI(uri, getter_AddRefs(channel));
if(NS_FAILED(rv)) return rv;
// bytes = iStream.available();
nsCOMPtr<nsIInputStream> iStream;
rv = channel -> Open(getter_AddRefs(iStream));
rv = iStream -> Available(&bytes);
buffer = (char*)nsMemory::Alloc(bytes);
if (!buffer) return NS_ERROR_OUT_OF_MEMORY;
// success = iStream.read(buffer, bytes)
rv = iStream -> Read(buffer, bytes, &success);
// check for 'BM' in header or 0x4D42, 19778
bmpType = (((PRInt32)buffer[0])&0xff)|
((((PRInt32)buffer[1])&0xff)<<8);
// check for compression type, 24 or 8 bit bmp
compType = (((PRInt32)buffer[30])&0xff)|
((((PRInt32)buffer[31])&0xff)<<8)|
((((PRInt32)buffer[32])&0xff)<<16)|
((((PRInt32)buffer[33])&0xff)<<24);
if((bmpType == 19778) && (compType == 0))
{
// get the offset of the first pixel byte
n = (((PRInt32)buffer[10])&0xff)|
((((PRInt32)buffer[11])&0xff)<<8)|
((((PRInt32)buffer[12])&0xff)<<16)|
((((PRInt32)buffer[13])&0xff)<<24);
/* the first 32 pixel bytes form a 32-bit integer
which is the offset of the last pixel that contains
information
*/
if(n>0 && (n<(PRInt32)(bytes-n-4)))
{
j=31;
lastPixel = lastPixel & 0x0;
for(i = n; i <= n + 31; i++, j--)
{
iByte = (((PRInt32)buffer[i]) & 0xff);
tBit = iByte & 0x1;
tBit = tBit << j;
lastPixel = lastPixel | tBit;
}
caplen = lastPixel / 8;
caption = (char*)nsMemory::Alloc(caplen + 1);
if(!caption)
{
nsMemory::Free(buffer);
return NS_ERROR_OUT_OF_MEMORY;
}
//Read the next pixel(at i) up to lastPixel
//j - used to shift the bits and to tell if we have filled a byte
//k - tells the current offset within caption
//c - character
j = 8;
k = 0;
c = c & 0x0;
for(; i <= lastPixel; i++)
{
j--;
cByte = ((buffer[i]) & 0xff);
cBit = (cByte & 0x1) << j;
// shift the bit to the left j times
c = c | cBit;
// if one byte is complete
if(j == 0)
{
caption[k] = c;
j = 8;
c = c & 0x0; // reset to 0
k++; // increment offset
}
}
*_retval = caption;
}// end of if
else
{
*_retval = msg2;
}
}//end of if
else
{
*_retval = msg1;
}
nsMemory::Free(buffer);
return NS_OK;
};
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