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cannot produce Targa(tga) image with transparent background
Posted: 2011-03-16T01:16:44-07:00
by academy25
Hi all, I have a QImage (QT's image class) with transparent background. I use the following code to convert it to a Magick image.
Code: Select all
Magick::Image* TgaFileType::toImage(QImage& qimage)
{
Magick::Image *newImage ;
double scale = 1 / 255.0;
Magick::PixelPacket *pixels;
Magick::ColorRGB mgc;
newImage = new Magick::Image(Magick::Geometry(qimage.width(), qimage.height()), Magick::ColorRGB(0.5, 0.2, 0.3));
newImage->modifyImage();
for (int y = 0; y < qimage.height(); y++) {
pixels = newImage->getPixels(0, y, newImage->columns(), 1);
for (int x = 0; x < qimage.width(); x++) {
QRgb pix = qimage.pixel(x, y);
mgc.red( scale*qRed(pix) );
mgc.green( scale*qGreen(pix) );
mgc.blue( scale*qBlue(pix) );
mgc.alpha( scale*qAlpha(pix) );
*pixels++ = mgc;
}
newImage->syncPixels();
}
return newImage;
}
But when I write the resulting Magick image to file, the background all seems black. However, when I save the original QImage as png via
, the transparency is preserved.
Code: Select all
Magick::Image* image = toImage(*imgOriginal);
image->write(dstFilename);
The more weird thing is, even if I set the alpha directly to zero, via
and save the Magick image, it does the same thing resulting with a fully black background image.
How can I set alpha values to produce a transparent Targa image?
Re: cannot produce Targa(tga) image with transparent backgro
Posted: 2011-03-16T07:26:40-07:00
by magick
Call newImage->matte(true) to tell ImageMagick you want to respect the matte channel, otherwise the alpha values are ignored. Also make sure that there is not a problem with the TGA image format. Save to PNG with newImage->write("image.png"). Otherwise your code should work (we tried a mock example of your code and returned the correct results with ImageMagick 6.6.8-4).
Re: cannot produce Targa(tga) image with transparent backgro
Posted: 2011-03-16T08:39:31-07:00
by academy25
hello, I have modified the above toImage function as follows,
Code: Select all
Magick::Image* TgaFileType::toImage(QImage& qimage)
{
Magick::Image *newImage ;
double scale = 1 / 255.0;
Magick::PixelPacket *pixels;
Magick::ColorRGB mgc;
newImage = new Magick::Image(Magick::Geometry(qimage.width(), qimage.height()), Magick::ColorRGB(0.5, 0.2, 0.3));
newImage->modifyImage();
for (int y = 0; y < qimage.height(); y++) {
pixels = newImage->getPixels(0, y, newImage->columns(), 1);
for (int x = 0; x < qimage.width(); x++) {
QRgb pix = qimage.pixel(x, y);
mgc.red( scale*qRed(pix) );
mgc.green( scale*qGreen(pix) );
mgc.blue( scale*qBlue(pix) );
mgc.alpha( scale*qAlpha(pix) );
*pixels++ = mgc;
}
newImage->syncPixels();
}
newImage->matte(true);
newImage->magick("PNG");
newImage->write(&blob);
newImage->read(blob);
newImage->write("C:\\tgapng.png");
return newImage;
}
but again the tga output and png output has a black background with no transparency.
The following is the input png image with a transparent background(you can save and open it via photoshop or any software that you can check its transparent part) ,
http://img820.imageshack.us/i/transparanlena.png/
And following is the png result written by the above code
http://img828.imageshack.us/i/tgapng.png/
Re: cannot produce Targa(tga) image with transparent backgro
Posted: 2011-03-16T09:25:49-07:00
by magick
A couple of things to try. Move the matte() method before the loop. Its possible your QImage pixels are not correct. Instead set
- mgc.red( scale*qRed(pix) );
to
and do that for green, blue, and alpha. See if you get a semitransparent gray image.
Re: cannot produce Targa(tga) image with transparent backgro
Posted: 2011-03-16T10:13:23-07:00
by academy25
It works fine for png, I got a semi-transparent image. But it fails for tga, there is no transparency, I just got a gray image.
Did you succeed for the tga case? Would you please try to obtain a semi-transparent tga image with the same code?
Re: cannot produce Targa(tga) image with transparent backgro
Posted: 2011-03-16T10:19:44-07:00
by fmw42
This works for me in CLI
convert logo: -transparent white logot.png
convert logot.png logot.tga
The colors are slightly different but the transparency is there.
Re: [SOLVED] cannot produce transparent Targa(tga) image
Posted: 2011-03-16T11:22:54-07:00
by academy25
The problem is solved, didn't know that the opacity values are inverted in ImageMagick: 0 for fully opaque and 1.0 for fully transparent !!
So I subtracted the alpha value that belongs to QImage from 255, before scaling the result by 1/255.
Code: Select all
mgc.alpha( scale*(255-qAlpha(pix)) );
Setting the matte to 'true' before the loop, and considering the inverted alpha values solved the problem.
