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Sizing images for digital projection

Larry Allen , Jan 04, 2006; 05:32 p.m.

What size should a digital image (tif) be sized for projection with a digital projector? I am hoping to use some tif's for a program. I don't know the model of the projector, it belongs to the auditorium. Previously they have only been using Jpegs and have used them just as they came from the camera. Maybe I should just save them as Jpegs?

Thanks

Responses

Simon Meeds , Jan 04, 2006; 05:43 p.m.

Ideally you need to know the resolution of the projector and mach the resolution of the computer to it, then assuming you want to show your images full screen you should make your image files the appropriate size: VGA 640x480; SVGA 800x600; XGA 1024x768; etc.

The most common projector resolutions today are SVGA and XGA, though some high-end units probably have higher specification: 1152x864, 1280x720, etc.

If you don't manage to find out what resolution the projector is, then I would suggest sizing your images to XGA. XGA is the lowest resolution which is really useful for photographic purposes and is supported by most modern projectors whether of higher or lower native resolution. The computer should be set up to XGA. If the projector only has native support for SVGA, for example, it will reduce the resolution produced by the computer, if it supports a resolution higher than XGA it will perform interpolation. In either case the output is unlikely to be ideal, but if the auditorium management can't be bothered to let you know the resolution of the projector they can't really expect any better.

Good luck with your presentation.

Dennis Price , Jan 04, 2006; 05:46 p.m.

Just think of a digital projector as a computer monitor, and size your pics accordingly.

800x600 at 72dpi is a typical size. Some projectors handle 1024x768 or larger. If you can't determine beforehand, perhaps it would be a good idea to make two versions of your presentation using those two different sizes.

Unless you know that the application program will support TIFFs, I would suggest you use jpegs as they are probably more universal.

Simon Meeds , Jan 04, 2006; 05:55 p.m.

Anyone who mentions dpi in relation to this question has no idea what dpi means - dots per inch. It's only relevant for printing. A projector shows even better than a monitor how unapplicable it is to electronic display... just move the projector or change the zoom - where does your dpi go then?? Forget dpi, you're only concerned with pixels!

Dennis Price , Jan 04, 2006; 06:03 p.m.

Oops, sorry about including the ref to dpi. Didn't even realize that I typed that in. Fingers sometimes go faster than my brain.

My apologies if I caused any confusion...

Jim Strutz - Anchorage, AK , Jan 05, 2006; 11:08 p.m.

I agree that XVGA (1024x768) is probably the best option unless you can find out the resolution of the projector. I have seen a few reasonably priced SXVGA, or XSVGA (1280x1024, I think) projectors recently, but unless they just bought it, or spent a fortune for one last year, the resolution is probably no more than XVGA.

I also agree that JPG files are the better way to go with this. The files are smaller and they will load faster for smoother transitions. If they, or you, are using a very fast computer with plenty of RAM it may not matter, but JPG is more universally supported by projection / slide show programs. The difference in quality will not be seen by anyone.

Are you using your computer, or the one at the auditorium? If not yours, how are you going to transport your images (CD, USB drive), and how are you loading them into the display program? What program will be used for display? Power Point is commonly used in a lot of places, but there are far better options for displaying slides/images.

John Reynolds , Aug 26, 2008; 08:50 a.m.

When I follow the directions above (size the image to 1024x768 and reduce the dpi to 72) the image starts to pixelate on my monitor at 'fit to screen' size. Even when I reduce the dpi to only 150 this happens, only less. At the original dpi of 300 and sizing the image to 14"(the horizontal dimesion of my 19" monitor), the image is fine. Since, as I understand it, a projector will project what appears on the monitor it seems that dpi DOES matter. As does size - sizing the image to 1024x768 produces an image that is 3.413"x2.28" and even at 300dpi (in fit to screen mode) the image shows pixelation. So using the directions posted here will produce a very poor result. Something is either wrong with the instructions posted here or with the way I'm applying them.

Jim Strutz - Anchorage, AK , Aug 26, 2008; 12:11 p.m.

Wow! This thread is almost three years old -- a lot has changed since then. Higher resolution projectors for one, and more powerful computers that can handle the larger resolution images for another.

But John, you ARE applying this wrong. Most LCD or DLP projectors still have less resolution than your 19" monitor, (probably 1280x1024 or 1280x960) so taking a 1024x768 image and fitting it to your monitor WILL show pixelation as it interpolates the image up to fit. That's normal. But on the XGA projector it will still look great. The computer doesn't take the image on your monitor and display that on your projector. It renders the image file to both devices separately if it has a dual display video adapter in the computer, and if it has a single display adapter for two ports the output devices themselves will still render the image differently. So the advice still stands; adjust your image for your final output device.

You can size the image to look best on your monitor if you want, and then the XGA projector will interpolate it down to 1024x768 as it displays. And if you are looking for the best looking image on BOTH machines that's the best way to go, as final down rezzing by the projector is better than up rezzing to fit the monitor. However, sizing an image to fit a higher rez device than necessary is a waste of bandwidth. Faster computers with more memory makes that mostly a mute point however.

And no, setting dpi still makes no difference on either monitor or projector. Only the size in the number of pixels matters. Resetting dpi AND the image dimensions together changes the total number of pixels, and that's what you are seeing.

John Reynolds , Aug 28, 2008; 08:08 a.m.

Yes the thread is old - that's the wonder of a Google search! In the process I discovered this site which has all sorts of great information.

I played around with the infomation you gave me and you were right - the pixelation I was seeing was from upsizing a 1024x768 image to my monitor size. Sizing the images to my monitor resolution (1280x1024) solved the problem.

In the end, I elected to size my images to a monitor width of 14" since, in this case, the jury chairman will be operating the computer and projector for the jury members and I want him to see clear as possible images on the monitor. Doing this brought the pixel count to 2100 on the horizontal side increasing the file size a bit but, as you mentioned, most computers today should be able to handle this.

Thanks for responding to my post. I was starting to panic and can now make my submission with confidence.

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