Version: 4.2.0 SVN (using Devel)
Compiler: 4.2.4 vanilla
Installed from: Compiled sources
Every other existing web browser can show PNG images while they are being loaded.
Konqueror cannot do that.
Are you talking in a standalone viewer? What viewer are you using?
Open any heavy enough (say > 2MB) PNG file in Konqueror like http://kde.org/announcements/announce_4.2-beta2/desktop.png
Firefox/Opera/IE will show this file progressively line by line, while Konqueror will only display this image after it has been fully downloaded.
Maksim asked you to tell which image viewer do you use? (View-> View Mode -> which one is selected). I can reproduce this behavior when using gwenview kpart, but embedded image viewer displays PNG image progressively.
I have now done the following: I ran Konqueror, then went to Settings -> Configure Konqueror -> File Management -> File Associations -> Image/PNG -> Embedding and set "Embeddable Image Viewer" the first in the "Service Preference Order". Now images are being shown correctly (progressively).
However the bug is that "Embeddable Image Viewer" should be set as default for Web browsing, because I cannot justify using GwenView kpart for the simple task of viewing PNG images in Konqueror.
Gwenview has a lot more functionality, such as zooming. The "Embeddable Image Viewer" is just a thing wrapper around KHTML's internal decoders. Anyway, I bet bug 178406 is about the same issue; let's hope the reporter of that responds.
*** This bug has been marked as a duplicate of bug 178406 ***
I cannot see how these two bugs are related to each other but you probably know better. However I still believe that PNG images in Konqueror should be handled by "Embeddable Image Viewer" as it is far more convenient for users (and after all you can later open the images in GwenView if you want to transform them).
I do not think 178419 is the same as this one. 178419 is about the lack of incremental display of images while they are loaded. Something the Gwenview KPart still lacks.
This bug also applies for standalone JPEG and GIF images. I think until Gwenview KPart supports incremental display of images the defaults should be changed.
KDE 4.4 still suffers from this problem.
Still the issue in KDE 4.5 beta 1.
Still broken in KDE 4.6 beta 1.
At least in Fedora 21 this bug is fixed because Fedora uses GwenView by default.
Is GwenView the default in new KDE versions or it's only Fedora?
Gwenview is a standalone local image viewer, which as far as I can tell isn't relevant to the originally reported issue in Konqueror.
Seems to be fixed in neon-testing-20200602-1042.iso (had to install via apt install konqueror) and also Konqueror seems to be abandoned.