Magick ++未加载TGA Blob

Question

I have a buffer containing the data for an RLE-compressed 8-bit RGB TGA image. I want to load this into a Magick++ Image but I keep getting

Magick: no decode delegate for this image format `' @ error/blob.c/BlobToImage/353

Here is my code

#include <Magick++.h>
#include <fstream>

int main(int argc, char** argv)
{
    std::ifstream file("window_borders.tga", std::ios::binary | std::ios::ate);
    std::streamsize size = file.tellg();
    file.seekg(0, std::ios::beg);

    char* buffer = new char[size];
    if (!file.read(buffer, size)) return 1;

    Magick::Blob data_blob(buffer, size);
    Magick::Image m_image(data_blob);

    return 0;
}

If I identify it I get

window_borders.tga TGA 330x390 330x390+0+0 8-bit sRGB 33106B 0.000u 0:00.000

Annoyingly, if I specify this info, then it works just fine. I can even convert it:

Magick::Image m_image(data_blob, Magick::Geometry("330x390"), "TGA");

m_image.magick("JPEG");
m_image.write("test.jpg");

And indeed test.jpg and window_borders.tga look identical. Why can't it detect the format automatically?

Answer 1

Why can't it detect the format automatically?

The TGA format never really had a unique "magick-number" header, or some other quick+reliable way to identify if a TGA exist within a blob.

If I remember correctly, later extended version of TGA introduced the string TRUEVISION-XFILE as a magick identifier, but at the files footer table.

I'm not an expert, but I imagine some software designers would be shaking their heads.

Now, not only are you responsible for knowing the file format ahead of time (by given filename) , but have to fully & correctly read the image-header to determine where the image-data stops, and the image-footer starts.

I would guess that this would be a large contributing factor into why there's no IsTGA method like we have IsPNG , IsTIFF , and so on...

As you've previously discovered one solution.

Magick::Image m_image(data_blob, Magick::Geometry("330x390"), "TGA");
// This should work too.
Magick::Image m_image(data_blob, Magick::Geometry("0x0"), "TGA");

But you can also do the following.

Magick::image m_image;
m_image.magick("TGA");
m_image.read(data_blob);