XnView Software

Not to be confused with "progressive JPEG", just to get that out of the way.

I'm suggesting displaying files as they load. This will make for a much snappier experience, because there will not be the (ever so slight) delay before a file is displayed. Incremental display is the same thing that web browsers do, and it works for almost every kind of file.

So I'm not saying this will be faster, I'm saying it will "feel" faster. Also it will allow the user to keep going from picture to picture, having loaded each one to, say, half-way, while each half-loaded picture is visible enough to the user in the process.

ok, but only XnViewMP has this feature

I tried it, but I don't see this happening.

In a directory with lots of large pictures, it's easy to see that a picture gets loaded either completely or not at all. But I certainly don't see it displaying incrementally.

Sorry, XnViewMP load picture at lower resolution and after high resolution (not progressive)

I see, so that's why it makes no difference when viewing large pictures on a slow medium (say, camera photos on an SD card).

Would it be a good idea to implement true incremental loading/decoding?

No you are right, I think the author and I must have misunderstood the meaning of "incremental display".

I was talking about displaying a picture the way a browser does. And let me tell you it feels faster when an image viewer has implemented this. It feels a LOT faster, even on a fast medium showing small pictures. Why? because it starts displaying something *instantly*, rather than after the delay caused by loading&decoding.

XnView works like this:
1. Image is fully loaded into memory
2. Image is displayed in low quality
3. Image is displayed in high quality.

As Pierre has pointed out, there is no such thing as progressive loading. If I get you (thany2) right, you would like a different loading:
1. Part of Image is loaded into memory
2. Part of Image is displayed in low quality
3. If there are more parts, repeat Step 1. Otherwise: Display whole image in high quality

Loading a part of an image and displaying it right away before loading the next part might work for some file formats (and compression types), but not for all file formats. I guess this is the reason why XnView does not support partial loading and displaying.

It works for PNG, JPEG, BMP and "simple" TIFF. Those are the most widely-used formats iyam.

/edit
It will work for ANY kind of those files. Interlaced/progressive has nothing to do with incremental display (which is a misconception I have oftenly seen happening).

To be perfectly clear: just like a web browser
Those guys can do it, too.