Multiframe Dicom file not readable by some viewers

Question

I have developed a program in C++ that works in 2 major steps :

• extract frames from a video with ffmpeg and convert them to jpeg ffmpeg -i videofile.mp4 -q:v 1 -r desired_framerate tmp_04%d.jpeg

• create a multiframe Dicom file from those jpeg images via DCMTK

  //Example for one image
  
  // Get the n-th image
  QFile* imageFile = new QFile("Path/To/Image");
  
  // Read the image inside a byte array
  QByteArray * ba = new QByteArray();
  imageFile->open(QIODevice::ReadOnly);
  *ba = imageFile->readAll();
  
  // Insert the byte array in the Dicom file
  cond = jpegPixelItem->putUint8Array(reinterpret_cast<Uint8 *>(ba->data()), ba->size());
  
  // Rinse and repeat
  

It works well and can be displayed on most viewers but some complain about the Transfer Syntax being wrong. As of now, I'm using the "JPEGLossless:Non-hierarchical-1stOrderPrediction" but It seems some viewers can't read my Dicom file unless I change the Transfer Syntax to "JPEG Baseline (Process 1)" which is a lossy Transfer Syntax.

I assume the problem comes from the first step of the program with ffmpeg that might be creating lossy JPEG images but I'm not sure because I'm using the "best" q:v scale as I've seen in other posts on the subject.

Therefore, my 2 main questions are:

• why do some viewers have no problems displaying the dicom file whereas some others can't?
• is there any way to obtain lossless JPEG images from a ffmpeg command?

Answer 1

why do some viewers have no problems displaying the dicom file whereas some others can't ?

Probably because they catch the inconsistency between the TransferSyntaxUID in the DICOM header and the encapsulated JPEG data which is lossy JPEG.

is there any way to obtain lossless JPEG images from a ffmpeg command ?

AFAIK there is no way to guarantee mathematically lossless compression with the frame extraction of ffmpeg. But with DCMTK you could convert the resulting DICOM image to other formats. The command line tool dcmdjpeg can be used directly or serve as an example how to extend your code to do that.

Although it cannot be technically verified, I advise against pretending the image being losslessly encoded. The MPEG stream does have a lossy compression.

If you store the DICOM image as lossless JPEG, I strongly recommend to set Lossy Image Compression (0028,2110) to "01" to avoid repeated lossy compression. See the tag desciption in DICOM