Here are some tips for people preparing photographs for showing on a digital projector. They're intended for anyone presenting work at a Redeye event, but should be useful more generally for presentations and slideshows.

Sizing images

Projectors come in a range of resolutions or pixel dimensions. At Redeye we usually use projectors that are 1024 x 768 pixels, or 1400 x 1050 pixels. Both of these are in the ratio of 4:3, a common ratio for presentation projectors.

However we sometimes encounter venues with widescreen projectors; either 1920 x 1080 or 1920 x 1200 pixels. 

In each case, the first number is the horizontal dimension.

If you don't know the resolution of the projector, we recommend sizing images to fit the highest projector resolution you are likely to find. So horizontal images should be 1920 pixels across, and vertical images 1200 pixels high. Square images 1200 pixels square. In any of these cases, a little larger is fine.

At the time of writing (2016), 4K projectors are occasionally used. These provide much larger dimensions. If you know your images will be projected on a 4K projector, find out the native resolution and prepare images accordingly.

File format and compression

Problems can arise if images are very large, which can slow down the slideshow software. This particularly applies to large TIFFs and sometimes JPEGs that have been saved at maximum quality.

When you are saving images for projection, use JPEG format. When you save each image you should be offered a range of quality settings and we recommend Level 8 in Photoshop, also known as 60% or the lowest “High” setting. This provides the best compromise of size and quality. Do not use the “maximum” or level 12 quality setting - this can slow the slideshow down.

If you are familiar with colour management, we recommend saving images in the sRGB colour space. Most projectors have an sRGB preset which should be a close match for this space. Remember to use “Convert to profile” not “Assign profile” if using Photoshop - the latter will give incorrect colour.

Borders

Some photographers like to put borders round their images when preparing them for projection. If you want to show your images at their strongest, this border should be black. We advise against using white borders. While white might look good on your computer screen, many projectors project a very bright white, which can dazzle viewers and make the images harder to look at. If you want that effect or need a visible border (ie not black), we suggest trying a mid grey.

Software for preparing images for a slideshow

If you are asked to send a slideshow in advance, there are two options in common use. You can prepare a slideshow in Microsoft PowerPoint, or just send JPEGs.

In PowerPoint: you have control over any text, transitions and slide backgrounds. However there are occasional problems with mismatched screen ratios. You should find out in advance whether the projector ratio is 4:3, 16:10 or 16:9.

One other problem with PowerPoint is that it doesn’t automatically save movies inside a presentation. If your PowerPoint includes movies, make sure to send the movie files along with the PowerPoint file.

As JPEGs - the main problem here is when images are projected in the wrong order. Be careful when numbering images. Many people use a numbering system like 1smith.jpg, 2smith.jpg ... etc. The problem with that is the computer reads the first character first. So 11smith.jpg will appear before 2smith.jpg. To get round this problem, use a three digit numbering system and start from 100. So 100jones.jpg, 101jones.jpg ... etc will work perfectly. 

Sending or supplying presentations

If you are sending in advance, you can send presentations as email attachments up to about 20MB. Larger than that you will need to use a file transfer system such as mailbigfile.com.

If you are bringing a presentation, the best thing is to put it on a USB flash drive. Bring a spare as these drives can fail.

Using your own laptop

If your presentation is in a particular software format, such as Apple Keynote, or if you will be using lots of different applications, demonstrating techniques, or making last-minute changes, you might want to use your own laptop. In which case:

 - Make sure you, or the event organiser, has the appropriate adaptor.

 - Charge your battery fully or bring a mains cable.

It’s also possible to project from a phone or tablet. You’ll definitely need the appropriate adaptor.

Improving the quality of projected photographs

If there’s a choice for the connection between laptop and projector use a digital (HDMI, Thunderbolt or Mini DisplayPort) rather than analogue (VGA) connector.

It’s quite common to see blown out highlights, clipping and other problems in projections. Most projectors default to a bright and contrasty preset, intended for graphics in a lowish ambient light level, but not darkness. If you know what you are doing it’s possible to improve things. Using the projector remote control, select a different preset such as sRGB, or reduce the gamma or contrast setting. If you have more time you can try calibrating the projector from system preferences, settings or control panels.