[libcamera-devel] [PATCH] qcam: saveImageAs: Set image quality explicitly

[Laurent Pinchart]

Hi Kieran,

On Thu, Mar 19, 2020 at 12:32:38PM +0000, Kieran Bingham wrote:
> On 18/03/2020 15:41, Laurent Pinchart wrote:
> > On Wed, Mar 18, 2020 at 03:13:36PM +0000, Kieran Bingham wrote:
> >> The QImageWriter defines a method to set the output image quality.
> >> Explicitly set it to 95 to override any defaults.
> > 
> > You could add, although it's a Qt implementation detail, that by default
> > the JPEG image handler uses a quality of 75, which isn't considered high
> > enough ?
> 
> Indeed, some element of 'ringing' has been observed in the output
> images, so I have increased the quality level.
> 
> Thank you for determining the default setting, I hadn't identified what
> the QT5 default was. I assumed I could get Qt to tell me, but the
> .quality() method returns -1 for me :-(
> 
> I can update the commit message to:
> 
> "
> The QImageWriter defaults to an image quality value of 75 which can lead
> to perceivable visual artefacts.
> 
> Improve the quality of the output by explicitly setting the image
> quality to 95.
> "

Works for me.

> >> Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> > 
> > Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > 
> >> ---
> >>  src/qcam/main_window.cpp | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/src/qcam/main_window.cpp b/src/qcam/main_window.cpp
> >> index ae1760dfd647..1869fdfc8679 100644
> >> --- a/src/qcam/main_window.cpp
> >> +++ b/src/qcam/main_window.cpp
> >> @@ -360,6 +360,7 @@ void MainWindow::saveImageAs()
> >>  		return;
> >>  
> >>  	QImageWriter writer(filename);
> >> +	writer.setQuality(95);
> >>  	writer.write(image);
> >>  }
> >>  

-- 
Regards,

Laurent Pinchart