by Hi,
I am trying to read a .jpg file using "The Independent JPEG Group's JPEG
software".
in C++ Builder 1.0.
In my project, I tried the code in example.c file of the Software.
I have used a loop to insert raw data to Image1->Canvas. But it is very
slow.
I have only added the code below to the function (read_JPEG_file (char *
filename)).
I am looking for a faster method managing the same work.
Thanks in advance!
Mehmet
int d1, d2, d3;
d1 = 0;
while (cinfo.output_scanline < cinfo.output_height) {
(void) jpeg_read_scanlines(&cinfo, buffer, 1);
// put_scanline_someplace(buffer[0], row_stride);
// my code
for (d2=0, d3=0; d2 < cinfo.output_width * 3; d2+=3, d3+=1) {
Image1->Canvas->Pixels[d3][d1] = RGB (buffer[0][d2],
buffer[0][d2+1], buffer[0][d2+2]);
}
d1++;
}
And the complete function:
void __fastcall TForm1::read_JPEG_file (char * filename)
{
/* This struct contains the JPEG decompression parameters and pointers to
* working space (which is allocated as needed by the JPEG library).
*/
struct jpeg_decompress_struct cinfo;
/* We use our private extension JPEG error handler.
* Note that this struct must live as long as the main JPEG parameter
* struct, to avoid dangling-pointer problems.
*/
struct my_error_mgr jerr;
/* More stuff */
FILE * infile; /* source file */
JSAMPARRAY buffer; /* Output row buffer */
int row_stride; /* physical row width in output buffer */
/* In this example we want to open the input file before doing anything
else,
* so that the setjmp() error recovery below can assume the file is open.
* VERY IMPORTANT: use "b" option to fopen() if you are on a machine that
* requires it in order to read binary files.
*/
if ((infile = fopen(filename, "rb")) == NULL) {
fprintf(stderr, "can't open %s\n", filename);
Application->Terminate();
}
/* Step 1: allocate and initialize JPEG decompression object */
/* We set up the normal JPEG error routines, then override error_exit. */
cinfo.err = jpeg_std_error(&jerr.pub);
jerr.pub.error_exit = my_error_exit;
/* Establish the setjmp return context for my_error_exit to use. */
if (setjmp(jerr.setjmp_buffer)) {
/* If we get here, the JPEG code has signaled an error.
* We need to clean up the JPEG object, close the input file, and
return.
*/
jpeg_destroy_decompress(&cinfo);
fclose(infile);
Application->Terminate();
}
/* Now we can initialize the JPEG decompression object. */
jpeg_create_decompress(&cinfo);
/* Step 2: specify data source (eg, a file) */
jpeg_stdio_src(&cinfo, infile);
/* Step 3: read file parameters with jpeg_read_header() */
(void) jpeg_read_header(&cinfo, TRUE);
/* We can ignore the return value from jpeg_read_header since
* (a) suspension is not possible with the stdio data source, and
* (b) we passed TRUE to reject a tables-only JPEG file as an error.
* See libjpeg.doc for more info.
*/
/* Step 4: set parameters for decompression */
/* In this example, we don't need to change any of the defaults set by
* jpeg_read_header(), so we do nothing here.
*/
/* Step 5: Start decompressor */
(void) jpeg_start_decompress(&cinfo);
/* We can ignore the return value since suspension is not possible
* with the stdio data source.
*/
/* We may need to do some setup of our own at this point before reading
* the data. After jpeg_start_decompress() we have the correct scaled
* output image dimensions available, as well as the output colormap
* if we asked for color quantization.
* In this example, we need to make an output work buffer of the right
size.
*/
/* JSAMPLEs per row in output buffer */
row_stride = cinfo.output_width * cinfo.output_components;
/* Make a one-row-high sample array that will go away when done with image
*/
buffer = (*cinfo.mem->alloc_sarray) ((j_common_ptr) &cinfo, JPOOL_IMAGE, r
ow_stride, 1);
/* Step 6: while (scan lines remain to be read) */
/* jpeg_read_scanlines(...); */
/* Here we use the library's state variable cinfo.output_scanline as the
* loop counter, so that we don't have to keep track ourselves.
*/
Image1->Width = cinfo.output_width;
Image1->Height = cinfo.output_height;
int d1, d2, d3;
d1 = 0;
while (cinfo.output_scanline < cinfo.output_height) {
(void) jpeg_read_scanlines(&cinfo, buffer, 1);
// put_scanline_someplace(buffer[0], row_stride); // instead of
this line I used the lines below.
for (d2=0, d3=0; d2 < cinfo.output_width * 3; d2+=3, d3+=1) {
Image1->Canvas->Pixels[d3][d1] = RGB (buffer[0][d2],
buffer[0][d2+1], buffer[0][d2+2]);
}
d1++;
}
/* ///////Burasy thumbnail i?in
// Genitlik i?in cinfo.output_width deeerinin istenen thumbnail
genitlieine b?lnmesi
// gerekir. Eeer bu deeer 2 ise d2+=3 olan deeer d2+=6 olur.
// Ykseklik i?in cinfo.output_height deeerinin istenen thumbnail
ykseklieine b?lnmesi
// gerekir. Eeer bu deeer 3 ise d1%3==0 olur.
d1 = 0;
d4 = 0;
while (cinfo.output_scanline < cinfo.output_height) {
(void) jpeg_read_scanlines(&cinfo, buffer, 1);
if (d1%4==0) {
for (d2=0, d3=0; d2 < cinfo.output_width * 3; d2+=12, d3+=1) {
Image2->Canvas->Pixels[d3][d4] = RGB (buffer[0][d2],
buffer[0][d2+1], buffer[0][d2+2]);
}
d4++;
}
d1++;
}
*/
ReleaseDC(Panel1->Handle, hdc); file://benim uydurmam
/* Step 7: Finish decompression */
(void) jpeg_finish_decompress(&cinfo);
/* We can ignore the return value since suspension is not possible
* with the stdio data source.
*/
/* Step 8: Release JPEG decompression object */
/* This is an important step since it will release a good deal of memory.
*/
jpeg_destroy_decompress(&cinfo);
/* After finish_decompress, we can close the input file.
* Here we postpone it until after no more JPEG errors are possible,
* so as to simplify the setjmp error logic above. (Actually, I don't
* think that jpeg_destroy can do an error exit, but why assume
anything...)
*/
fclose(infile);
/* At this point you may want to check to see whether any corrupt-data
* warnings occurred (test whether jerr.pub.num_warnings is nonzero).
*/
/* And we're done! */
Quote:}