<![CDATA[Qt6 reading JPEG encoded as Progressive using more memory (sometimes till out-of-memory) than Baseline]]>Hey all,

  • We are using Qt6 on an embedded device (ARM64 imx8) with limited RAM (total about 400MB).
  • While loading JPEG image (Iink) which is encoded as progressive in an Qt Widget application :-
    bailey.jpg: JPEG image data, JFIF standard 1.02, resolution (DPI), density 72x72, segment length 16, progressive, precision 8, 7360x4912, frames 3
  • using QImageReader::read to read image scaled to 30px x 30px instead of 7360px x4912px :-
     // Reader for JPEG
 QImageReader reader("bailey.jpg");
 reader.setScaledSize(QSize(30, 30)); // directly decode at 30x30

 QImage image30x30;
 if (!reader.read(&image30x30)) {
     qWarning() << "Failed to load:" << reader.errorString();
     return -1;
 }
  • Even though a scaled down version of image e.g 30px x 30px is asked
    • From my understanding that memory used during decompression (using IDCT shrink-on-load from libjpeg (link)) should be :-
      width × height × channels × bytes per channel = memory (MB)
    • calculation for above image :-
      7360 * 4912 * 3 * 1  = 103MB
    • But since we are asking for a scaled version so libjpeg would scale to 1/8 as its theoratical limit
      (7360 / 8 ) * (614 / 8) * 3 * 1 = 1.7MB
    • so expect it to maximum consume 1.7MB and not 103MB
    • may be i am wrong about it but this is just little knowledge of how i have it
  • During the read, it seems like it is loading whole image that it causes out-of-memory for kernel to kill the application eventually.
  • The default QJpegPlugin linked is libjpeg :-
    $ ldd /usr/lib/plugins/imageformats/libqjpeg.so 
...
libjpeg.so.62 => /usr/lib/libjpeg.so.62 (0x0000ffffbd350000)
  • But when same image was converted from progressive to baseline (Iink) then it did use some memory but not till out-of-memory
    bailey.jpg: JPEG image data, JFIF standard 1.02, resolution (DPI), density 72x72, segment length 16, baseline, precision 8, 7360x4912, components 3
  • Therefore the question is :-
    • does QJpegPlugin and eventually libjpeg can they handle progressive images efficiently or is it a bug or limitation of library itself?
    • or should we convert JPEG to baselines as it seems to respect the downscaling and not load whole image into memory ?
]]>https://forum.qt.io/topic/163221/qt6-reading-jpeg-encoded-as-progressive-using-more-memory-sometimes-till-out-of-memory-than-baselineRSS for NodeWed, 23 Sep 2026 23:02:57 GMTFri, 12 Sep 2025 08:07:31 GMT60<![CDATA[Reply to Qt6 reading JPEG encoded as Progressive using more memory (sometimes till out-of-memory) than Baseline on Fri, 12 Sep 2025 08:59:10 GMT]]>
  • I added the links to the image in the description above but adding under again :-
  • yeah sure i added that as a bug to be checked by the Qt Team :-
    • ]]>    https://forum.qt.io/post/831504https://forum.qt.io/post/831504Fri, 12 Sep 2025 08:59:10 GMT    <![CDATA[Reply to Qt6 reading JPEG encoded as Progressive using more memory (sometimes till out-of-memory) than Baseline on Fri, 12 Sep 2025 08:12:45 GMT]]>Please provide a small jpeg and create a bug report. I can only think that libjpeg does either something wrong here or the Qt plugin does not handle a specific combination of parameters correctly.

    ]]>    https://forum.qt.io/post/831503https://forum.qt.io/post/831503Fri, 12 Sep 2025 08:12:45 GMT