Jaggies in Polar Coordinates filter

JS
Posted By
John_Shanks
Jul 28, 2004
Views
353
Replies
9
Status
Closed
Is there a way to improve on the Polar Coordinates (rectangular to polar) filter? It is producing a low resolution image with jagged edges.

I suspect it is mapping FROM pixels of the original image (then crudely interpolating) rather than mapping TO pixels of the new image, which would be preferable. However I could be wrong.

PanoTools does a much better job (see here <http://www.spacific.net.nz/polar/> for an example comparison) and I might just have to buy it, but if the Photoshop filter can be made to do the job then all the better.

Any ideas?

Thanks.

(PS CS, Mac G4, typical image 4000 by 4000, but seems to occur on any size)
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CC
Chris_Cox
Jul 30, 2004
Hmm – something is wrong. I have never seen Photoshop’s polar coordinates produce aliased samples like that. At a minimum, it always does bilinear interpolation.
JS
John_Shanks
Jul 31, 2004
Thanks Chris.

For a 1000 x 1000 image there isn’t much difference but the PanoTools method is still better. Basically the jaggies get worse as you move out from the origin. This makes me suspect that the Polar Coordinates filter has been programmed poorly: possibly using fixed increments of the polar angle (say one-hundredths of a degree or radians, or whatever). This is fine near the origin and for smaller images, but for larger (e.g. 4000 x 4000) images the angle increment is large in pixel terms out towards the edge.

Well that’s what I suspect. As a test perhaps you or others can try this:

Create a new 4000 x 4000 image, white background. Using the Line Tool in fill-pixel mode, draw an 8 pixel wide line across the image almost at the bottom. Now apply the Polar Coordinates filter. I have added part of what I get to the link here <http://www.spacific.net.nz/polar/>. I would be most interested to hear if others get a smoother result (and how!).

(Incidentally, I have interpolation set at Bicubic (Better).

Many thanks.
CC
Chris_Cox
Jul 31, 2004
The current version does use fixed point math – but it should work fine up to about 8000 pixels across.

And the plugin doesn’t know anything about the app interpolation preferences.
JS
John_Shanks
Jul 31, 2004
Thanks Chris,

"but it should work fine up to about 8000 pixels across"

Maybe it should, but it doesn’t — well, not for me!

If someone could try my test mentioned above I would be most grateful, then I’ll know whether it’s just me, and I can act accordingly.

Cheers
SS
Susan_S.
Jul 31, 2004
John – yup, I get the exact same results as you do. It looks pretty horrid. (I run panotools in my copy of Elements in Classic mode so I can use the original freeware version)
JS
John_Shanks
Jul 31, 2004
Susan, many thanks for taking the trouble. Panotools it is then! Strange that Adobe are either unaware of the filter’s poor quality, or haven’t got round to fixing it. It’s a very simple formula for the transformation.
P
progress
Aug 1, 2004
although normaly, useably = no errors
JS
John_Shanks
Aug 2, 2004
Well OK the Panotools filter takes longer, but who cares? I am happy to wait the 20 secs it takes for a 4000 pixel wide image. In fact I would gladly wait 5 minutes if I knew I would get a good result. Using the polar filter isn’t something one wants to do repeatedly and often anyway.
CC
Chris_Cox
Aug 5, 2004
John – can you email me () an image that you would normally apply Polar Coordinates to? I’d like to test my ideas and see if the quality is acceptable to you.

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