setGamma/setQuality to QImage

[ArmanS]

Hi All,

I'm need toset/get gamma and quality/compression to/from QImage. There is very little documented about it. What I've been able to do so far is the following (e.g. for Quality):

int getImageQuality(const QImage &image)
{
  Q_ASSERT( !image.isNull() );
  QByteArray byteArray;
  QBuffer buf(&byteArray);
  buf.open(QIODevice::WriteOnly);
  QImage imageTemp(image);
  if (imageTemp.save(&buf, "PNG")) {
    QImageReader reader(&buf);
    return reader.quality(); // IT REACHES HERE. BUT ALWAYS RETURNS -1
  }
  return -1;
}
 
void setQuality(int Q) // MY TEST VALUE IS 50
{
  QByteArray ba;
  QBuffer buf(&ba);
  buf.open(QBuffer::ReadWrite);
  QImageWriter writer(&buf, "PNG");
  writer.setQuality( Q ); // SETTING A TEST VALUE 50
  bool ok = writer.write( myImage() );
  Q_ASSERT( ok );
  if (ok) {
    QImage img;
    ok = img.loadFromData(ba, "PNG");
    Q_ASSERT( ok );
    if (ok) { 
      qDebug("Quality = %d", getImageQuality(img)); // ALWAYS RETURNS -1
    }
  }
}

int getImageQuality(const QImage &image)
{
  Q_ASSERT( !image.isNull() );
  QByteArray byteArray;
  QBuffer buf(&byteArray);
  buf.open(QIODevice::WriteOnly);
  QImage imageTemp(image);
  if (imageTemp.save(&buf, "PNG")) {
    QImageReader reader(&buf);
    return reader.quality(); // IT REACHES HERE. BUT ALWAYS RETURNS -1
  }
  return -1;
}

void setQuality(int Q) // MY TEST VALUE IS 50
{
  QByteArray ba;
  QBuffer buf(&ba);
  buf.open(QBuffer::ReadWrite);
  QImageWriter writer(&buf, "PNG");
  writer.setQuality( Q ); // SETTING A TEST VALUE 50
  bool ok = writer.write( myImage() );
  Q_ASSERT( ok );
  if (ok) {
    QImage img;
    ok = img.loadFromData(ba, "PNG");
    Q_ASSERT( ok );
    if (ok) { 
      qDebug("Quality = %d", getImageQuality(img)); // ALWAYS RETURNS -1
    }
  }
}

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SO, but it's not working. as if no effect.
Can you please help me with this?

Thanks in advance!!

[wysota]

PNG is a loseless format, it doesn't support changing the quality.