How Do I Prepare Images for Digital Projectors?

I was wondering if anyone has done any tests of digital projectors and preparing images for projection? Or if you might have any resources you could point me to?

The situation is that I’m getting involved in some local camera clubs and for their meetings and competitions they require 1024x768 images that get projected to around a size of around 152x114 cm. And then the commentator stands right up next to the screen and comments that every image lacks sharpness. I’d like to give them some reference as to what should be expected in this situation and what distance the commentator and judges should view these projected images from.

Thanks in advance for any direction on this.

One could actually use the last two calculators I provided on the page about digital photo enlargement to first back-calculate the minimum viewing distance (based on 20/20), and then for that distance one could apply the appropriate sharpening (by calculating the PPI projected on screen at that distance/resolution).

Just by crude estimates, for your scenario this would come to a viewing distance of 15 ft for someone with 20/20 vision (when projected to ~150cm max dimension). At that distance there would be roughly 18 pixels per inch.

This calculation is actually in part based on an old Adobe white paper on sharpening from a long time ago. Even though it was intended for print enlargement, it should follow that it applies equally to projection images. The only difference might be that some projectors soften the image more than others (DLP vs Lcos vs LCD, etc), so you may need to over-sharpen a bit to compensate. Hope this helps.

Thanks! I will try out the calculators and pass along the information to the group.

Another issue is the colour space. Clubs specify sRGB for digital projection whereas Adobe 1998 is commonly used for image editing and simply assigning the sRGB profile results (on my monitor at least) in a loss of saturation and when the image is projected it looks a little washed out. Should I therefore increase the saturation after assigning the sRGB profile?

Thanks for any guidance. Regards, Tony

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Originally Posted by Tony

Another issue is the colour space. Clubs specify sRGB for digital projection whereas Adobe 1998 is commonly used for image editing and simply assigning the sRGB profile results (on my monitor at least) in a loss of saturation and when the image is projected it looks a little washed out. Should I therefore increase the saturation after assigning the sRGB profile?

Thanks for any guidance. Regards, Tony

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Hi Tony, welcome to CiC!

You want to convert the color space, not assign it. Simply assigning a sRGB color space to an AdobeRGB image is the same as viewing an AdobeRGB image in a non-color managed application. When you convert the color space, out of gamut colors will be clipped, but you will not need to adjust your saturation (In fact, on anything less than the highest quality displays you shouldn't even notice a difference).

The trick for projectors looking good is made up of two things: 1. It must be used in a very (very) dark room, and 2. The brightness/contrast settings must be correct. I own a ColorMunki for my calibration and profiling, it has the ability to calibrate and profile projectors. If you have some funds to purchase one then you will see a dramatic difference on the projector - especially since they are constantly being used under various lighting conditions, the bulbs start to dim as they age etc.

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Originally Posted by KentDub

When you convert the color space, out of gamut colors will be clipped

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Hi Kent,

Whether OOG colours are clipped depends on what rendering intent is used. Relative colorimetric and absolute colorimetric will clip, but perceptual won't.

One point which I don't understand about digital projectors is what is the optimum pixels per inch size of the original photos?

Because of my ignorance in this subject; when I have needed to supply images for various talks, etc, I have just copied the images to a CD and handed it to the presenter with the 'You may need to resize them before use' caveat.

They usually show OK but I have never discovered if any resizing was done. And judging by the apparent lack of any satisfactory answer, I suspect the users didn't understand what resizing meant anyway.

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Originally Posted by Geoff F

One point which I don't understand about digital projectors is what is the optimum pixels per inch size of the original photos?

Because of my ignorance in this subject; when I have needed to supply images for various talks, etc, I have just copied the images to a CD and handed it to the presenter with the 'You may need to resize them before use' caveat.

They usually show OK but I have never discovered if any resizing was done. And judging by the apparent lack of any satisfactory answer, I suspect the users didn't understand what resizing meant anyway.

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The PPI of the projector is basically an effect - but not one you can control. It is completely dependent on the distance the projector is from the screen. Assuming they will display your image full screen, you should size and sharpen your images to the native resolution of the projector. The DPI (akin to PPI) settings within photoshop/metadata are completely ignored in this situation. Windows-based systems like to run at 96-DPI internally, but again, it's completely dependent on the display connected to it (as to the true/effective dpi). Because projects can throw a very large screen, in order for the image to look good, you must factor in viewing distance. The farther away the "sharper" the image (pixels become closer together; denser). Sharper might not be the best word - but it will look better from a farther distance. If you so desire you can calculate the optimum distance by taking the screen size and resolution of the screen, and calculate the viewing distance proportional to a standard monitor.

Ask the media guy working the event what the resolution of the projector is, and confirm that he will be showing everything fullscreen. Again, all you'll need to do is resize and sharpen for the resolution he gives you.

Put it this way Geoff - "you can't have too much information in an image - but you can have too little". It's really only a question of how big the resultant files will be; on the Internet that's important, but if they're on a CD then size really isn't so much of a concern.

Hi Kent and Colin,

Thanks for the help on color space vis a vis the preparation of images for DP, the advice is very helpful.

Best wishes, Tony

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Originally Posted by Tony

Thanks for the help on color space vis a vis the preparation of images for DP, the advice is very helpful.

Best wishes, Tony

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No worries Tony - that's what they "pay us the big bucks" for ;)