Image resizing for projection

[Lon Howard]

Hi,

Gosh I feel almost guilty about asking a question since I said I was back but then disappeared again, but my other life has been too crazy. Anyway ...

Every time I have submitted digital images for projection, the rules always call for image resizing in addition to converting to jpegs. Now I have to do the projecting myself for a Lions Club program and have been practicing with the projector at home. It appears that all of the psd files I have tried are projecting just fine on a blank wall at home. They have not been resized or converted to jpegs. So I'm wondering why the images should be resized or converted, not only in this case, but in general as well since you always experience some loss of image quality when they are resized. There's got to be an answer ... any ideas are greatly appreciated.

[Dave Humphries]

Hi Lon,

For you, what you do works, but if you submit images to another party, they won't want humongous PSD files for competitions, since they take longer to transfer/load and may require PS or similar to view them (depending what apps are installed on the computer).

Jpg is a standard format for image display - and you should convert to the sRGB colorspace also, since I doubt a projector will be better than this.


For web, or I believe projection, you should always downsize to the native resolution of the display device*, so that one image pixel = 1 display pixel exactly. As long as full screen is used, this ensures that a 1:1 relationship exists and no interpolation of pixels occur.

It is particularly the 'on the fly' resizing/zooming (in or out), by browser or Windows, that kills image sharpness.

* After downsizing you should, no must, output sharpen, which avoids the loss of quality you are referring to and help it look its best at the new resolution.
Try USM (UnSharp Mask) with something like 80-100% amount, 0.4px radius and 0 or 1 threshold.

So the first thing you need to know is the native resolution of the projector to be used.

By the way, this answer is provided 'from theory', if anyone with practical experience can give a better answer, or correct any errors in mine, please do speak up.

[Manfred M]

Check the specs of your projector and prepare your files to whatever native resolution it puts out. Often they have an even lower resolution than your typical computer screen (the one I use a lot at work is around 1280 x 720 max) and I would be very surprised if it even comes close to doing sRGB.

[Mike Buckley]

Dave and Manfred nailed everything.

The only other thing I can suggest is to make sure your projector is not displaying a color cast. The reason I mention this is that I have used two digital projectors (mine and my friends' projector) and the default settings on both of them displayed a noticeable yellow cast. I was able to easily alter the settings in my projector to eliminate the yellow cast. I don't know if that would have been possible using my friends' projector, as I use my projector when showing photos in their home.

[tclune]

Check the specs of your projector and prepare your files to whatever native resolution it puts out. Often they have an even lower resolution than your typical computer screen (the one I use a lot at work is around 1280 x 720 max) and I would be very surprised if it even comes close to doing sRGB.

I think Manfred nailed it. I took a photography class that used basically this kind of technology for reviewing students' work in-class. The projector would decimate the photos for projection, which had anywhere from no effect to a devastating effect on the images. The photos that were most impacted ended up looking grainy and specular -- the instructor used the term "pixillated,' which is evocative of the effect if inaccurate. The particular device used for that class did not up-res, so you were better off resizing to a bit too small than being a bit large. Obviously, I don't know whether your system has a similar problem, but that is something to watch out for. FWIW

[Lon Howard]

Thanks to all of you for your insight. I actually have created some actions that do those kinds of things to my images that are going for projection; but now I know what to look for in order to be able to detect the deficiencies in images that have not been resized. So far the only differences I've seen are the loss of quality in the downsized images but I haven't gone through very many images yet; so I will fine tune my pixel peeping and provide some feedback later, right now I'm up against a time clock to get about a hundred or so ready to present tomorrow. Thanks again!

[FrankMi]

For what it is worth Ron, I have visited two local camera clubs that use projectors in their meetings for contests and in both cases, what should have been outstanding images based on the originals, were displayed so horribly by the projectors that it wasn't worth submitting digital images for viewing.