The positive impact of iOS 5 on the quality of iPad panos

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Wim.Koornneef
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Thu Oct 13, 2011 2:22 pm

Hello Forum,

I found some interesting things regarding crashes and quality of Pano2VR panos with iOS 5 on iPad v1.

1) The number of panos with tiles of 960px that can be open in the tabs is now 5 without crashing Safari Mobile (was 1 in iOS 4.3.2),
2) Large tiles are not crashing the app anymore (I could open a pano with tiles of 1900 px without any issue),
3) Large tiles can differ a lot in image quality (sweet spot for best quality is a tile size of 1440 px, the worst quality is 1472 px).

Here are 3 zoomed in and cropped screenshots of panos on my iPad v1 with tiles of 960px, 1440px and 1472px, judge for yourself...

Image
Image
Image

I like to ask people with iPad v2 to do some tests yourself, I increased the tile size with steps of 32px as this seems the best blocksize of webkit.
(1440 px=45 blocks of 32px and 90 compression blocks of 16px)

Tip1, use a high quality compression of 95,
Tip2, make a screenshot (PNG) of the pano on iPad when zoomed in and compare the filesize of the screenshot, the tile size that performs best (sharpness wise) will always have the largest filesize of the screenshot.

I like to hear about the results of tests with iPad v2, I expect (but this has to be tested), that for iPad v2 the optimum tile size is also 1440px.

Best,
Wim
Last edited by Wim.Koornneef on Fri Oct 14, 2011 8:46 pm, edited 1 time in total.
DemonDuck
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Thu Oct 13, 2011 6:36 pm

Why would tile size affect image quality of output like that?????
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Wim.Koornneef
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Thu Oct 13, 2011 7:13 pm

DemonDuck wrote:Why would tile size affect image quality of output like that?????
I don't know, I can only guess what is going on.

When testing in steps (960-1100-1300-1500-1700-1900) I found out that the image quality slowly improves with each larger tilesize, this improvement suddenly stopped with 1500 px. After some more testing I found the sweet spot at 1440px.

It turns out that from 960px to 1440px the quality improves a bit with larger sizes, then it falls down at the lowest quality level at 1472 px and from there it improves again very slowly up to 1900+ (I stopped testing at 1900 px).

Wim
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360Texas
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Thu Oct 13, 2011 9:29 pm

Thanks Wim. I copied your test results over to:

http://gardengnomesoftware.com/forum/vi ... 775#p24775
Dave
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wtb
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Sun Oct 16, 2011 3:43 pm

off topic:

after i installed iOS 5 on iphone 3Gs loading time in safari for HTML5 now very fast and no lag during rotation, so apple improved safari :D
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360Texas
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Mon Oct 17, 2011 4:02 pm

Vim

Cube face size is 1 part of the issue. Need to know

Original image set dimension h x w pixels. Your tested final stitched panorama dimensions h x w pixels.

For your optimized 1440 cube face size... I wonder if your final stitched image was near 4500 pixels wide ?
For your optimized 1900 cube face size ...I wonder if your final stitched image was near 6000 pixels wide ?

Constant = 3.1415
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Wim.Koornneef
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Mon Oct 17, 2011 5:38 pm

Hello Dave,

I think the size of the equi is in my case of no importance because they are large enough to create panos of 2880 px so the input size is defenitely sufficient to create even much larger tiles then 1900 px.
Btw, the series of test panos for the iPad where created from the same equi I used to create a 2880 px Flash pano.

I did not mentioned it before but I also tested the same series of iPad panos with Safari on my iMac.
On this system the enhancement of the quality with larger tiles is much more visible then on iPad, the 1900 px tiles pano is clearly offering the best IQ.

When comparing the IQ on iPad and iMac then it is also clear that the drop of quality with the tiles of 1472 px is only present on the iPad, not on the iMac, so the weird fall back of the quality on the iPad must be caused by some unknown processing of the image tiles.

Wim
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360Texas
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Mon Oct 17, 2011 6:33 pm

Just trying to help develop your work

Ipad original and Ipad 2 screen size are ■1024-by-768-pixel resolution at 132 pixels per inch (ppi) http://www.apple.com/ipad/specs/

Back in 2009 Erik Leeman also did some calculations
http://tech.groups.yahoo.com/group/Pano ... sage/33879

"Then choose a screen size that you think is big enough to cater for, and size
your cube faces accordingly:

vertical FOV = 60º (zoom ratio = 0.75)

targeted.......required.....suggested
screensize.....cubeface.....cubeface
1024x768......1330x1330.....1360x1360
1280x800......1386x1386.....1424x1424
1440x900......1558x1558.....1600x1600
1680x1050.....1818x1818.....1872x1872
1920x1200.....2078x2078.....2128x2128
2560x1440.....2494x2494.....2560x2560 "

Targeted screen size is referring to a monitor or mobile device screen. I guess this might be why we use cube face tile sizes to match the screen display for a mobile device or a desktop monitor

I am looking for Ken Turkowski's online pano calculator. Knowing the pano width I think Ken has a working forumla for determining the optimum cube face size needed for a viewer to dispaly a panorama.

I found this in Panoguide forum http://www.panoguide.com/forums/qna/7553/

[update]
Ken Turkowski's world link must have been relocated because now it points to a medical page. Anyone remember Ken's online pano calculator page and where it went to ?
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Wim.Koornneef
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Mon Oct 17, 2011 7:53 pm

Hello Dave,

The optimum tile resolution for a given screen depends on the fov, it makes a lot of difference to have a fov of 60 or 75 degree so calculating the optimum tile size is in practice only usefull when the fov is always the same. Also the zoom-in factor makes a huge difference, a lot of people will try to avoid any overzoom and limit the zoom to a 1:1 pixel ratio for screen and image.

My approach is a bit different, I try to keep it as practical as possible and I use image sizes that are not based on theoretical optimums but based on practical use like f.i. the loading time of a pano, will it crash or not, can I use a little overzoom and does it still look good, etc.

I think I am done testing, I showed the results of the improvement, the drop of IQ at 1472 px on iPad 1 and the fact that iOS 5 can handle up to five Pano2VR 960px panos on iPad 1 without crashing (*).

(*) I posted an article with a video clip on the PanoToolsNG forum about this, in case you missed it here is the article and the clip:
http://panotoolsng.586017.n4.nabble.com ... 01492.html
http://www.dmmdh.nl/forum_images/ios5_p ... panos.html

I like to ask you to do some testing yourself with your iPad 2 with iOS 5 installed.
It is not hard to do, just take a equi that is large enough for outputing a regular Flash pano and then make a htmlcss3 pano with tiles of 1440px and another one with tiles of 1472px and check them on your iPad 2.

I like to know the result, is the difference in IQ the same as on my iPad 1 or not.
If not then perhaps you can find a sweet spot for the iPad 2 by outputing some larger and smaller tiles.
Your help is much appriciated.

Success,
Wim
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