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Old Oct 29, 2009, 8:33 AM   #1
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Default Accidental posting discovery

Just for your information, I have this morning accidentally produced a beautiful lesson in how not to post images in these forums if you want them to look as sharp as expected, at...

http://forums.steves-digicams.com/landscape-photos/161532-autumn-bathroom-window.html#post1014246

I had returned to the forums after a break, and found that my usual posting technique produced an unsharp result when displayed in my browser. On investigation, I realised that this was due not to my technique or any change in the Forums; it was the nature of the image, a very fussy autumnal foliage picture, demanding more compression after resizing than I usually find necessary.

I have left both images in place in that thread, as I suspect with hindsight that several other regular participants may have fallen into the same trap.

Nice to be back
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Old Oct 29, 2009, 8:51 AM   #2
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Alan:

If you exceed the maximum file size allowed (currently set to 260000 bytes, or approximately 253.9KB) or dimensions (currently set to 1024 pixels on the widest side for easier viewing without scrolling on more monitors), the forums software will try to downsize the images (and recompress them at a lower jpeg quality) to try and allow members to upload them anyway (even if they are not within the limits you'll see set when you upload photos). That's what is probably causing the degradation you're seeing.

We used to prevent attaching images if the file size and/or dimensions in pixels were too large for the limits you'll see on the screen for attaching images to posts. But, so that members could upload them anyway, the forums software is now resizing and recompressing images that exceed the set limits. This process also removes the EXIF.

So, for best results, make sure to stay within the limits for both file size and dimensions you'll see when uploading images. That way, the forums won't need to resize and recompress them using a lower JPEG Quality.
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Old Oct 29, 2009, 11:09 AM   #3
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Quote:
Originally Posted by JimC View Post
...exceed the maximum file size allowed (currently set to 260000 bytes, or approximately 253.9KB) or dimensions (currently set to 1024 pixels on the widest side for easier viewing without scrolling...
....the forums software is now resizing and recompressing images that exceed the set limits..
Yes, thanks, Jim. I think doing an automatic resize is an excellent idea, so long as one realises it's happened.

I now think I may indeed have noticed when this change happened, because just before I went on summer holiday I'd found myself having difficulty in displaying a few images suffuciently sharply. To my astonishment I found myself getting a better result using a straight 'pixel resize' and no sharpening, than my usual fancy interpolation methods plus a bit of USM. I expect I'd find these were fussy foliage, hence oversized images, if I could remember which ones they were!

The curious thing is that today's offending image was resized not to 800x600 (which it was already, so it didn't need it) but to 799x599, when I'd optimised it for 800 by 600. As sharpness is an optical illusion based on edge effects, I suspect that may be enough to undo the sharpness. I'm neither a physicist nor a visual perception psychologist, so this is a guess. Maybe someone properly qualified in those fields as well as digital imaging might spot this thread and comment!

Thanks again for the explanation,
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Old Oct 29, 2009, 11:14 AM   #4
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The downsizing algorithms being used leave something to be desired (image quality is relatively degraded if downsizing is attempted by the forums software, since it's not real "smart" in that area [yet]).

So, I'd be careful to stay within the set resolution and file limits to avoid that kind of thing. Your results are typical (it's going to downsize a bit first, hence your notice of the slight decrease in dimensions, and apply a relatively strong jpeg compression, which will degrade quality considerably over what you could accomplish yourself with an editor). There are pros and cons to that approach (denying the ability to upload photos that exceed the set limitations as the forums were setup before, or trying to accommodate more users by attempting to resize/recompress images to stay within the set limits without more work from the member posting the photos)
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Old Oct 29, 2009, 11:21 AM   #5
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P.S.

The same thing applies to photos in albums here. Make sure to stay within the file size and resolution limits for best results. Here's one recent thread discussing it:

http://forums.steves-digicams.com/co...es-albums.html

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