strange image attachment display behaviour

[timelessbeing]

I attached two PNG images to a post. Both have identical dimensions. Both placed inline. Tags look simply like this:

Code: Select all

[attachment=2]venthose.png[/attachment]
[attachment=3]pcvhose.png[/attachment]

Why is one image rendered as a thumbnail with hyperlink to the actual image file, and the other is rendered full size with no hyperlink?

Link to actual post:
http://chevygmcvans.com/viewtopic.php?t=11053

Thanks.

phpBB 3.3.5

[Mick]

290C216D-20E9-4C5B-B796-BE312295836A.png (114.35 KiB) Viewed 2894 times

The second one I clipped a smidgeon and it shows, presumably, how it should? It’s probably to do with your image settings in ACP> Attachments. The create thumbnail should be yes and the thumbnail width/height should be small.

[timelessbeing]

it shows, presumably, how it should?

That is what I would expect. But even in your example ... the sizes are slightly different. The attachment dimensions are exactly the same (to the pixel).

It’s probably to do with your image settings in ACP> Attachments.

This does not explain why one attachment is displayed one way, and the second attachment is displayed another way.

The create thumbnail should be yes and the thumbnail width/height should be small.

Create thumbnail was set to yes.
"Maximum thumbnail width/height in pixel" was 400px.

[timelessbeing]

Let's try attaching the same files here ...

Well, well ... same problem on this forum.

[Mick]

Did the two pics start out life as screenshots? Can you convert them to jpeg and increase their size and see how they work. I’m just trying to determine if it’s an issue with screenshot pngs, pngs in general or something else.

FWIW - These two images are both jpegs taken with an iPhone and they’re a good deal larger than the thumbnail setting and work ok. I’m not certain what the issue is with your images. Can you try some pics similar to the below that are much bigger than the thumbnail setting on your board and see what happens?

[timelessbeing]

Did the two pics start out life as screenshots?

No. But why would it matter? An image is an image.

Here are they are converted to JPEG.

I'll try to find some more examples ...

[timelessbeing]

Here are some more B&W PNGs (677x610)

[Mick]

It looks to me that the pngs aren’t performing how we would expect in this case but the jpegs are. The reason I don’t know, maybe someone else will chime in.

Here are they are converted to JPEG

They seem to be working fine. viewtopic.php?p=15892826&sid=80cc017cf3 ... #p15892826

[timelessbeing]

Here are some larger B&W PNGs (1355 x 1221 px)

[timelessbeing]

and here are some small B&W PNGs (317 x 342 px)

[timelessbeing]

Well I think I've figured it out.
Thumbnail behaviour for PNGs depends on file size not file dimensions. The threshold seems to be 12 kB. Anything below gets displayed full size, no hyperlink, and includes file information caption (ex "pcvhose.png (11.4 KiB)"). Anything above is displayed in reduced size, hyperlinked to the original file, and no info caption.

I think this is undesirable behavior. As has been demonstrated, this creates an inconsistent viewing experience for images with the same dimensions.
I do not believe that PNGs of identical dimensions will differ so drastically in download time, that they would need to be displayed differently. The thumbnailing algorithm should be based on dimension, not file size.

[Gwyneth Llewelyn]

Wow, that was quite a discovery!... I was trying to understand why the behaviour seemed to be so inconsistent when using PNG instead of JPEG. Now I see why!