[vtkusers] Read PNG from in-memory buffer?

[Andras Lasso]

You can use libpng directly (it's included with VTK). See how it is done in the PLUS toolkit:
DecodePngImage(unsigned char* pngBuffer, unsigned int pngBufferSize, vtkImageData* decodedImage)
https://app.assembla.com/spaces/plus/subversion/source/HEAD/trunk/PlusLib/src/PlusDataCollection/BkProFocus/vtkPlusBkProFocusOemVideoSource.cxx#ln549

Andras

-----Original Message-----
From: vtkusers [mailto:vtkusers-bounces at vtk.org] On Behalf Of Elvis Stansvik
Sent: September 29, 2016 7:32
To: VTK Users <vtkusers at vtk.org>
Subject: Re: [vtkusers] Read PNG from in-memory buffer?

2016-09-29 13:29 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
> 2016-09-29 11:35 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>> 2016-09-29 9:29 GMT+02:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>>> I'd like to read a PNG from an in-memory buffer. Looking at 
>>> vtkPNGReader, it seems it only works with files in the file system. 
>>> In general, is there some way to use the reader classes in VTK with 
>>> in-memory data, or would I have to write my own custom reader?
>>>
>>> My need for this is not great, I was simply hoping to be able to 
>>> keep this particular PNG in the Qt resource system (so in the end, 
>>> embedded in my executable), load it using Qt file facilities, and 
>>> use VTK on the read in-memory data.
>>
>> I realize now that I can probable use QImage to load/decompress the 
>> image, and pass the uncompressed data to a vtkImageImport, but I 
>> can't find any docs on what format vtkImageImport expects for the pixels.
>> Anyone know?
>
> I had a go at this approach, using QImage::Format_RGBA8888 as I think
> (?) that's the format vtkImportImage wants, but the resulting image 
> looks garbled when shown in VTK:
>
>     // Load image with QImage
>     QImage image(":/images/orexplore-logo-80x47.png");
>
>     // Convert to RGBA8888
>     image = image.convertToFormat(QImage::Format_RGBA8888);
>
>     // Have a look at the image to make sure it's OK
>     auto debugLabel = new QLabel();
>     debugLabel->setPixmap(QPixmap::fromImage(image));
>     debugLabel->show();
>
>     // Import into a vtkImageData
>     auto imageImport = vtkSmartPointer<vtkImageImport>::New();
>     imageImport->SetDataSpacing(1, 1, 1);
>     imageImport->SetDataOrigin(0, 0, 0);
>     imageImport->SetWholeExtent(0, image.width() - 1, 0,
> image.height() - 1, 0, 0);
>     imageImport->SetDataExtentToWholeExtent();
>     imageImport->SetDataScalarTypeToUnsignedChar();
>     imageImport->SetNumberOfScalarComponents(4);
>     imageImport->SetImportVoidPointer(image.bits(), 1); // Note:
> QImage::bits() deep copies
>     imageImport->Update();
>
>     auto mapper = vtkSmartPointer<vtkImageMapper>::New();
>     mapper->SetInputData(imageImport->GetOutput());
>
>     auto actor = vtkSmartPointer<vtkActor2D>::New();
>     actor->SetMapper(mapper);
>
> Anyone know exactly what format vtkImageImport expects, or, if it 
> expects RGBA (unsigned char), why the above won't work?

Whoa. Just found
http://www.vtk.org/doc/nightly/html/classvtkQImageToImageSource.html
:) I'll of course use that. Sorry for the noise.

Still interested in why the above approach wouldn't work, out of curiosity.

Elvis

>
> Elvis
>
>>
>> Elvis
>>
>>>
>>> Elvis
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