Poor image quality of rendered .tiff files

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  • Updated 8 years ago
Hi
I work for Hasselblad and I am trying to render some .tiff files using seadragon-min.js. We have used this tool before without any issue but for images I am currently trying to render, I am get some noise or bad pixels in certain areas of the image. I have also tried using the "Create your own" function on the zoom.it website with the same result. The images are of very high quality (8956 x 6708 pixel) and as I said it has worked before but not now. I was wondering if it could have anything to do with the connection between where my images are lying on our server and the zoom.it server which receives the image. I can see from zoom.it website that is not yet possible to upload an image but is there any other solution to rendering the images. This rendering process was in place when I started working here so not 100% sure about all issues. Thanks

JohnK
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John Kelleher

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Posted 8 years ago

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Bill Crow, Seadragon Group Manager

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Hi John,

It would help to have a better understanding of exactly what type of artifacts you are seeing. Is there as sample image on zoom.it that you could point me to so I can see exactly what is being rendered?
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John Kelleher

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Hi Billy

Thank you for the quick reply, I am sorry I didn't get back to you quicker but last Friday was a bank hoilday here in DK and I was out of office yesterday. Anyhow here are some samples from zoom.it and I have also included some links to pages which we would like to have on our website but have not published them as yet due to the problems with the images. Having talked with the photographer who took the pictures he has given me a run down of the issues with the rendered images:

zoom.it/y33c - There are artifacts with regards to green and red colors around the end of the Barclays Bank sign. There are also blotches in the skyline, best seen between the top of the HSBC building and the building to the left (Alternative link: http://www.hasselblad.com/promotions/...)

zoom.it/qhrA - Image appears softer than the original image, this is an issue with most of the images which have been rendered. (Alternative link: http://www.hasselblad.com/promotions/...)

To best see the issues, you should download the originals, which you can do so from our website - http://www.hasselblad.com/sample-file..., when you compare the rendered images to that of the originals you will see the difference. I hope this is enough info to give an understand of the problems we are having but if you need anything else please contact me. Since we are a high end camera company, it is important that images we use on the web are of a high standard and as I said before we have used the tool to great effect previously and would like to continue to do so. Thanks again for your assistance

John

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John Kelleher

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Hi Bill

My apologises, just reading back through the mail and realise I spelt your name wrong. Sorry for the mistake

John
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John Kelleher

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Hi Bill

Hope all is well. I was wondering if there was any update with regards to the rendering issue I am having. It is of great importance that I find a solution to the problem with zoom.it soon as we need to go live with the comparsion views I sent you earlier. Hope we can find a fix.

Thanks for your help
John
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Bill Crow, Seadragon Group Manager

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Hi John,

I suspect the artifacts you are seeing are due to JPEG compression. zoom.it transforms the very large TIFF file into a tiled pyramid made up of hundreds of JPEG tiles at various resolutions to be able to provide the buttery-smooth, low latency pan/zoom animation. Both of the type of artifacts you identify would be typical of the lossy compression with color-subsampled JPEG files.

It's been years since I worked on this stuff, so I can't remember all the details of how we implemented zoom.it's conversion algorithm. A TIFF file is not a web standard file format, so we have to convert the format when we create the tiles and I suspect we default to JPEG for the conversion of any non-standard format.

However, PNG files are a standard web file format that also support lossless image encoding. I believe that we will convert a PNG source file to a tiled pyramid of PNG files rather than JPEG files. The interaction performance will suffer because of the larger file size of the uncompressed images, but it should guarantee that there is no quality loss due to JPEG compression.

So, I recommend that you try converting your source images to PNG files instead of TIFF files and then use the PNG file as the source for zoom.it. If my recollections on how everything works is correct, that should solve the problem.

If I can find any time tomorrow, I'll try to test it myself as well.

Bill
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John Kelleher

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Hi Bill

Thank you for the reply. I have tried rendering the images again after converting them to PNG and it fixes the artifacts issue. Unfortunately it doesn't solve the softness issue. I have done tests where I have adjusted the luminosity of the image and then rendered but the image still appears softer than the original. I don't know if you have download the original images but if you have below are 2 links to images (both converted to PNG format and luminosity adjusted) that where rendered in zoom.it. If you compare it with the original you can see a difference. Not sure if this can be fixed but if you have any possible suggestion that could fix it somehow that would be great.

http://zoom.it/v0u6

http://zoom.it/utm9

Thanks again

John
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Bill Crow, Seadragon Group Manager

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This is likely because Seadragon (Deep Zoom and zoom.it) is ALWAYS resampling and rescaling the image. To be able to deliver the zero latency continuous zooming, Seadragon is always showing a cross dissolve (with variable translucency) between images of two different scales. So, other than at very specific zoom positions, you are always looking at a cross dissolve between two different resampled views of different resolution tiles. I have no doubt that this will create some apparent softness at the pixel level.

Bill
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John Kelleher

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Hi Bill

Thanks very much for your help. It seems loading the images as png has solve the problem to a level which is appropriate for the photographer, so all good. Thanks again

John
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John Kelleher

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Hi Bill

I know I said we sorted the above issue but having created a comparison page, with zoom functionality, it has come to my attention that the image which appears on the right side has an issue. When I have similar images in a comparison view the image, although the same image on both sides, on the right side has a softness to the image. I was wondering if you have ever come across a similar issue before.

Thanks again

John