Forum : Advice & Critiques

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Topic: Image compression

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microwar (Over 1 year ago)
Do Photosynt compress the images before upload, and will a pre comression speed up the prosses (Precalc and upload)?
I can see a clear difference when i recompress the images from my camera (Canon eos450D) on my pc. (3.1MB -> 581KB). I can also see the uncompressed size is unchanged (28.8MB)

Is there a limmit on the resolution?
I tryed uploading 3880 x 2592 (10.1Mpix) some months ago, but the upload froze.
So now i just shrink them to 50%.
tbenedict (Over 1 year ago)
I've been uploading 4000x3000 images for a while.  It does work, but typically I'll do big uploads on a broadband connection.

Tom
Nathanael (Over 1 year ago)
Microwar,

All my synths since late December last year have been composed of 3872 x 2592 images and I have no problems with it. Sometimes, yes, there are errors with an upload, but I don't believe they have anything to do with the size of the images because I would occasionally have them before I got my current camera.

What Photosynth does is divide each of your photos into several resolutions and divide each of those resolutions into a series of jpg tiles. I don't know what quality setting it's saving those jpg tiles at, but if compression is taking place, it would be here. Before these collections of tiles are uploaded to the site, they are zipped up (.dzi = deep zoom image; dziz = deep zoom image zip). You can test this the next time you're making a synth by typing %temp%/photosynther into Windows Explorer and copying (not moving) one of your dziz files out of the images folder. Add .zip to the end of the filename and you should be able to peek inside.
Nathanael (Over 1 year ago)
Out of curiosity, what did you mean by "I can see a clear difference when i recompress the images from my camera (Canon eos450D) on my pc (3.1MB -> 581KB)"? Do you mean a difference when viewing these images outside of Photosynth or a difference in loading time/quality after using them in a synth?

Also, where are you reading the 28.8MB size at?

Thanks for any answers.

I suspect if there is a maximum resolution for images it would be quite high, since I belive Photosynth uses the same deepzoomtools.dll that Deep Zoom Composer uses to convert images to the dzi format.
microwar (Over 1 year ago)
When i download the images from my camera, they r in jpg format, but low compression, when i recompress this images on my pc(open the pic, and save it again in jpg), they drop down to around 10% of the original. I recompress images before uploading them to save time.

I tryed ones to upload a 200MB jpg (29556 x 14321, 1.2gig uncompressed) from nasa, but ran out of memmory.
Nathanael (Over 1 year ago)
As to the big NASA image, yeah that's pretty hefty. I imagine that anything using the deepzoomtools.dll would be capable of completing the job but since everyone has a different amount of RAM installed, it's likely a bit difficult to estimate where the limit of how large an image you'll be able to convert is on your machine.

I still say photos straight off of your camera should do just fine. A 10 maegapixel image is a fair bit less than a 423 megapixel image. :)

It really would be nice to have something built in to Deep Zoom Composer and Photosynth that would read the installed RAM and give you an estimate of the maximum sized image that your machine is capable of converting and specific per-image warnings if that estimate's boundary is transgressed.
NateLawrence (Over 1 year ago)
For several years now (if not in all of Photosynth's public availability) the only constraint on maximum individual photo size in Photosynth has been a file size of 32 megabytes.

Because JPEG compression is lossy compression (variable quality and thus variable file size, but never more than 99% of the original image's quality when decompressed), 32 megabytes does not correspond to any particular resolution.

The 32 megabyte per image limit does not apply to panoramas stitched with ICE http://bit.ly/microsoftice or Photoshop http://bit.ly/pstops

I believe that Photosynth has publicly stated which image quality they compress individual photos in a synth to, however I cannot find the quote at the moment.

The ICE team reports that they always save panoramas at 90% image quality when uploading to Photosynth, regardless of ICE's image quality setting.
https://twitter.com/natelawrence/status/131712820789248001
https://twitter.com/MicrosoftICE/status/131789532076064768
NateLawrence (Over 1 year ago)
As to microwar's question of reducing image file size prior to placing photos in Photosynth in hopes of speeding up processing and/or upload time...

>> Smaller data will take less time to upload.
>> Reducing image quality (and thus file size) without reducing resolution only makes your photos look worse. Photosynth will do this once, itself, regardless of whether you do or not.
>> Reducing image resolution will worsen the viewing experience for anyone wanting to zoom into your photos or combine your photos with others for a bigger synth of a particular subject.
>> Reducing an image's resolution will not lighten the processing load for Photosynth in image matching until you lower the resolution below 1.5 megapixels because Photosynth only uses a 1.5 megapixel version of each photo which is above that resolution for the image matching. After you get below that threshold, you will be robbing Photosynth of information which might have been used for useful matching.
NateLawrence (Over 1 year ago)
The most that I can really say is that in the coming years, the photos that we are taking today will look pitifully low resolution or low bitrate or low color gamut or low dimensionally. 

I believe that in ten years from now, you'll be happier if you chose the maximum quality allowable today.

Here an earlier discussion on the topic: 
https://getsatisfaction.com/livelabs/topics/what_image_quality_and_resolution_should_i_use
asdf
Cheungxin (2 months ago)
Interested in this topic and would like to see that in the coming years.
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http://www.rasteredge.com/solutions/image-compressing/
http://www.rasteredge.com/dotnet-imaging/image-compression/
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