Flickr causing Aliasing

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Hi all,

I have a quick query about Flickr. I've noticed that pictures I've uploaded are having aliasing added, which leads me to believe that the filtering used by Flickr is a bit odd.


zone-plate-canon1100d-large by GeordieCy, on Flickr

I created a zoneplate to see what the filters did. They do seem to cut the high frequency bits of the image, but they also alias.

Does anyone have any good workflow tips for Flickr? I'm wondering if the images need to be artificially softened before uploading?
 
No idea, can you post an example pic up on Flickr link it here and then explain what it is about the image that you think is wrong?
 
u8myufo said:
No idea, can you post an example pic up on Flickr link it here and then explain what it is about the image that you think is wrong?
Click to expand...

I've noticed that flickr seem to "process" images I upload to change the appearance.

Other photo sharing sites don't seem to have such "aggressive" filters.
 
boliston said:
I've noticed that flickr seem to "process" images I upload to change the appearance.

Other photo sharing sites don't seem to have such "aggressive" filters.
Click to expand...

Have you looked at this thread Adrian? Check out the two links I posted in post#15 in the first link and post#14 in the second one and see what you think then.
 
u8myufo said:
No idea, can you post an example pic up on Flickr link it here and then explain what it is about the image that you think is wrong?
Click to expand...

Hi,

I probably didn't explain the Zone plate well enough. The original image consists of concentric circles which get closer and closer together as they move towards the edge. At the edge the circles are 1 pixel wide.

When you scale the image, some of the information is necessarily lost (think of 2 pixels, 1 white, 1 black, if you scale this image to be only 1 pixel, this would be grey).

So for a perfect scaler, you'd expect the image I linked to to be a rectangle of detail surrounded by grey. You can't get a perfect scaler, so we get what is shown. The detail sort of bleeds off into grey with extra circles added. The aliasing is the extra detail the scaler has added.

One real pictures, this makes the picture artificially sharp and adds information where there wasn't any in the original .
 
TBH, I don't think it's doing too bad a job.

I took your full-sized original (there's your Creative Commons Attribution :)) and resized it to 800px wide in PSCS5 and I'm seeing more artefacts (particularly the abrupt cut-off lines in the circles) there than I am in the Flickr render to the same size in the OP.

Bicubic Sharper (which is what most people will use for a reduction)

zonePlate_800_bicubicSharp.png



Bicubic

zonePlate_800_bicubic.png



I don't think most people would think twice about using Photoshop for resizing and, if I've understood your explanation correctly, Flickr is doing a better job IMHO.

P.S. I've hosted these on a paid-for Photobucket account, but what I'm seeing on screen in the web browser accurately reflects what I see in the PNG files in Photoshop before I uploaded them.
 
Last edited:
Musicman said:
TBH, I don't think it's doing too bad a job.

I took your full-sized original (there's your Creative Commons Attribution :)) and resized it to 800px wide in PSCS5 and I'm seeing more artefacts (particularly the abrupt cut-off lines in the circles) there than I am in the Flickr render to the same size in the OP.

Bicubic Sharper (which is what most people will use for a reduction)

zonePlate_800_bicubicSharp.png



Bicubic

zonePlate_800_bicubic.png



I don't think most people would think twice about using Photoshop for resizing and, if I've understood your explanation correctly, Flickr is doing a better job IMHO.

P.S. I've hosted these on a paid-for Photobucket account, but what I'm seeing on screen in the web browser accurately reflects what I see in the PNG files in Photoshop before I uploaded them.
Click to expand...


Happy for anyone to use them. You're right about the Photoshop ones being slightly worse. Perhaps I'm just being truly picky. I've only seen the problem on an image of a field of grass in Flickr so thought I'd check.

It's more of an issue in video as the alias can moves in the opposite direction to camera motion.
 
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