QImage getting black areas for GIF frames

[ChrisW67]

Your code reads an image imageCount() + 2 times. I expect the last two images are the problem children.

QImage* image = new QImage();
QImageReader* reader = new QImageReader(gif);
reader->read(image);
 
for(int index=0;index<=reader->imageCount();index++)
{
reader->jumpToNextImage();
reader->read(image);
QString frameName = dir + '/' + QString("out%1.jpg").arg(index,5,10,QChar('0'));
image->save(frameName,"JPEG",100);
}

QImage* image = new QImage();
QImageReader* reader = new QImageReader(gif);
reader->read(image);

for(int index=0;index<=reader->imageCount();index++)
{
reader->jumpToNextImage();
reader->read(image);
QString frameName = dir + '/' + QString("out%1.jpg").arg(index,5,10,QChar('0'));
image->save(frameName,"JPEG",100);
}

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Line 3: reads first image in file (discarded)
Line 5: Loop of imageCount() + 1 iterations
Line 7: index == 0, jump to second image in file. index == 1, jump to third image...
Line 8: returns false (ignored) on last two loops

Try this on your problem image

const QString gif("test.gif");
QImage image;
QImageReader reader(gif);
qDebug() << "Count =" << reader.imageCount();
for (int index = 0; index < reader.imageCount(); ++index) {
    if (reader.read(&image))
        image.save(QString("output%1.png").arg(index, 3, 10, QLatin1Char('0')));
}

const QString gif("test.gif");
QImage image;
QImageReader reader(gif);
qDebug() << "Count =" << reader.imageCount();
for (int index = 0; index < reader.imageCount(); ++index) {
    if (reader.read(&image))
        image.save(QString("output%1.png").arg(index, 3, 10, QLatin1Char('0')));
}

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[elephant]

No I think that error was just introduced in the code to extract the images to a file for tests.

However, I did look more closely and the problem is the disposal method "Previous".

For examples see this page: http://www.imagemagick.org/Usage/anim_basics/#previous

Using your code with the example gif with disposal method "None" (http://www.imagemagick.org/Usage/ani...anvas_none.gif), frame #3 includes frame 2,1 and 0 all on top of one another. This is correct.

Using the gif with disposal method "Previous" (http://www.imagemagick.org/Usage/ani...anvas_prev.gif) frame #3 includes frame 2 and 1, but does NOT include frame 0. This is not correct.

I guess as a side question, does anyone know if there are options for how qt handles the disposal method?