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-   -   Image Resizing (http://e-group.uk.net/forum/showthread.php?t=47032)

Graham_of_Rainham 20th January 2018 03:55 PM

Image Resizing
 
I've posted the following on FaceBook, but value your collective input:

"I visit many photographic clubs and there is one reoccurring issue that is raised:

What is the "best" process for resizing images for projection?

Currently the PAGB standard for DPI is 1400x1050, but with cameras producing many times more resolution, how best can those millions of precious pixels be compressed down, so that the picture projected on a screen looks its best?

There are a great many "opinions" out there, but little by way of a consensus on what is considered the optimum solution.

Any links to good guides or information will be appreciated.
"

Thanks

wornish 20th January 2018 04:43 PM

Re: Image Resizing
 
TV s these days are moving to 4K resolution and even 8K is being demonstrated.

Ultra HD. 4K UHD (2160p) a resolution of 3840 pixels 2160 lines (8.3 megapixels, aspect ratio 16:9) and is one of the two resolutions of ultra high definition television targeted towards consumer television, the other being 8K UHD which is 7680 pixels 4320 lines (33.2 megapixels).

There are many projectors capable of 4K resolution at "reasonable" prices.

I would be very surprised if a projector capable of only 1400 x 1050 would be a match for those capable of 4K.

shenstone 20th January 2018 05:45 PM

Re: Image Resizing
 
When I do presentations I always try and find out what the projector native resolution is and resize appropriately

Having said that it also depends on how bothered I can be once it is down below a certain size the difference you will see on screen is limited

Therefore my usual 4/3 ratio is 1600x1200 (UXGA) and my default widescreen size is 1920x1200 (WUXGA)

Below that I will let the software/projector interpolate not expecting anyone to see much difference

Having said that when I recently had some of my pictures sown on a 4K projector with about a 100ft throw resulting in pictures about 15ft across and I did put in 4096x2160 (or that height on 4/3 format pictures) and they looked totally fabulous until the adaptor failed and we had to drop back to standard HD :-(

small point for you - not being involved with camera clubs I had never heard of PAGB so googled it and I found this on the Lancashire & Cheshire Photographic Union pages...

Quote:

You are probably aware that the PAGB have taken a decision to adopt a new standard resolution of 1600pixel by 1200 pixel for images entered into competition from July 2017
seems they are falling in line with me :-)

regards
Andy

sapper 21st January 2018 11:53 AM

Re: Image Resizing
 
I just export from LR to the size my club asks for, 1400px wide x 1050px high. I usually just fill in one of the boxes son I don't lose the ration of there image.

drmarkf 21st January 2018 02:21 PM

Re: Image Resizing
 
In Cambridge we moved to 1600x1200 when we upgraded our projector last year. We've just held our annual DPI competition for 35 local clubs at this resolution.

I must say I just check sharpening etc on screen in Capture One with the output set at whatever resolution is needed, and make any adjustments by eye before pressing the process button.

Graham_of_Rainham 21st January 2018 04:25 PM

Re: Image Resizing
 
Consider the situation of the person who has an image straight from the camera at: 5568 x 3712, which is also a 3:2 aspect ratio.

To get that down to 3840 2160, 1600 x 1200, 1400 x 1050 or 1024 x 768 (or any other ratio) requires a resize... So just how do you squash 5568 pixels into 1600 pixels ?

Each original pixel needs to be interpolated by a factor of 3.48, but exactly how do you choose which method is best?

There are a lot of different algorithms, some are good at some image content and others for different content... https://en.wikipedia.org/wiki/Image_scaling

So: If you are only viewing the image on a monitor which has a different resolution to the projector, you may get a nasty surprise, on club night, when the rigging lines of the yachts in the harbour look like a staircase. :eek:

I've seen many examples of regular patterns (railings, corrugated sheeting, etc.) that when compressed takes on the look of a bar code.

I've not found a "Learned Work" from any reputable source, that provides any guidance on this. The RPS is notably quiet on the whole subject... :o

wornish 21st January 2018 05:02 PM

Re: Image Resizing
 
All you can do is try it first on your computer i.e reduce it to the required pixel size for the projector and have a look for the compression artefacts that can be created. If your monitor resolution is less than the projectors then you have an extra challenge.

As you say there are lots of different algorithms available some work better than others.

birdboy 21st January 2018 05:26 PM

Re: Image Resizing
 
I am no expert on this but I wonder if you will get better answers from the Astrophotography world They are really concerned with image rescaling, there is something called binning. They really love their maths and algorithms.

https://pixinsight.com/doc/tools/Int...rResample.html

wornish 21st January 2018 05:31 PM

Re: Image Resizing
 
Quote:

Originally Posted by birdboy (Post 437991)
I am no expert on this but I wonder if you will get better answers from the Astrophotography world They are really concerned with image rescaling, there is something called binning. They really love their maths and algorithms.

https://pixinsight.com/doc/tools/Int...rResample.html

You are absolutely right. The Pixinsight developers in particular are notorious for their mathematical approach to all image processing.


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