What image size should I keep for photos of lecture slides, and does PPI matter?
Asked 12/7/2019
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2 answers
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I photograph presentation slides during lectures and training sessions so I can review them later, copy material into notes, or occasionally print them. I’m trying to decide what image size is sufficient for long-term storage while keeping files manageable.
Is something like 800×600 enough, or should I keep higher-resolution files? I’m especially concerned about slides with diagrams, musical notation, or small text.
I’m also confused about pixel dimensions versus PPI. For example, if an image goes from 3024×4032 at 240 ppi to 1512×2016 at 120 ppi, is that just a resolution change, or am I actually losing useful detail? Most of my viewing will be on a computer, not in print.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
4
I doubt that 800 x 600 is good enough. Some slides will most likely have more detailed information than can be stored at this resolution.
A good presenter will try to make everything readable from the back of the room. For pure text slides, this isn't hard to do. For diagrams, I and many people I know, will bend the rule and use very small text on diagrams. So, diagrams are where the highest resolution is needed.
Consider what resolution the projector will have. 1920 x 1080 are very common, higher resolutions are very expensive. I would store at 50% greater than the common resolution, storage is cheap. If you try to match the resolution, you may get interference patterns.
I would also consider videotaping the presentation with audio, if allowed. My slides often were "talking points", they didn't contain all the detail. The slides were expanded upon by me verbally.
Originally by user84623. Source · Licensed CC BY-SA 4.0
user84623
6y ago
0
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800×600 is likely too small for lecture slides, especially if they contain diagrams, notation, or small labels. For archiving, keep as many pixels as practical; storage is cheap, and you can always make smaller copies later. A useful rule of thumb is to keep at least around projector-level resolution, and preferably somewhat higher if your camera captured it cleanly.
The important number is pixel dimensions, not PPI. 3024×4032 contains far more detail than 1512×2016. If you reduced those dimensions, you discarded image data. Changing only the PPI metadata does not improve or reduce actual detail unless you also resample the image.
So for computer viewing, focus on preserving pixel count. Keep the original files if possible, and create resized copies only for sharing or convenience. If you overwrite the originals, you can’t recover lost detail later.
Also be aware that photographing digital projectors can produce banding, color artifacts, or partial frames. Test your camera settings with the projector when possible.
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