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I'm a techie and when attending various training presentations, I'll take a photo of a slide that is being presented.

Now I want to save this training slide for posterity.

What resolution is adequate for storing a training slide long term. The goal is that I should be able to read it, copy it to a MS Word document when creating a document that summarizes the event, or print it so I could read it.

My gut feeling is to use 800x600 but I have no technical basis for this.

I know there are a lot of factors that go into this. In one case, I'm attending a music lecture which highlights musical notation, in another lecture it's highlighting a powerpoint slide.

I'm not looking for perfect. I'm looking for an answer where 5 years from now I'll be happy with having information from a lecture that I attended and took notes but didn't put them into a MS Word document.

At this time, I'm resizing (in place) images using LightRoom and Photoshop so once I've resized them (in place) I can't go back to the original image.

A related question has to do with the resolution. I notice that the pictures I have taken are 240 pixels/inch. If I simply change the resolution to 120, the image size drops considerably. In one example,

3024 x 4032 @ 240 pixels/inch, 68.8M
1512 x 2016 @ 120 pixels/inch, 17.4M

Is it better to change the image size, and keep the resolution, change the resolution or change both. In general, I'm going to be viewing data on the computer (not printing). I realize for prints, you want to maintain a much higher resolution.

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  • 1. What's wrong with just using the native resolution of your camera? Storage is pretty plentiful these days. 2. Printer resolutions are typically 300-600 dpi, so 800x600 ends up being a 1-2 inch thumbnail when printed. 3. Consider asking the speaker for notes. If they're going to refuse on the basis of copyright or some such, they'd likely also frown on your photographing the slides. – xiota Dec 7 '19 at 5:40
  • Have you considered sketchnotes? You'll retain the info better and the notes will be much more meaningful for "posterity". – xiota Dec 7 '19 at 5:43
  • If you just want a single slide, the resolution doesn't matter as long as you can read it. If it's important enough, you can recreate the slide in the presentation software of your choice. – xiota Dec 7 '19 at 5:46
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    Isn't this the same exact question that is periodically asked by a new user, closed by the community, and then deleted by the OP (so not searchable the next time it comes up)? – Michael C Dec 7 '19 at 6:46
  • @xiota, years ago when the max size of an image was 1Kx1K, that was OK. The image sizes might be 4M, now they are 4K x 4K over 68M. I might start with an image that is 68M, and end up with one that is 1.8Meg. I don't want to pay for 30 to 40 times the cost for storage if I don't have too. – PatS Dec 10 '19 at 5:11
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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.

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There is one other thing to expect when photographing anything projected via an electronic projector (that is, by anything more modern than a slide projector or overhead projector):

Electronic projectors tend to do tricks like displaying all three color channels sequentially, going from color to color very quickly ... or not projecting all of the image at the exact same time... or taking short, millisecond "breaks" between frames ....

All this can really upset a video or photo camera in a lot of ways. You can get color artifacts, stripes, missing pieces of slide. So it is best to rehearse with the projector and camera you have, testing various settings until you find a combination of settings that reliably works - then stick with these settings.

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Is it better to change the image size, and keep the resolution, change the resolution or change both.

PPI means nothing until time to print or display. A 300 x 300 image can be 100PPI, 200PPI, 300PPI...it doesn't matter, it's still a 300 x 300 image.

When you took your example from 3024 x 4032 to 1512 x 2016, you killed off a lot of pixels. You didn't simply "keep the image size and change the resolution." No, you killed the image size. The resolution only matters so far as the display of said image. On a 72PPI screen, you've now a smaller image. If trying to print, you now have less detail and will be forced to print smaller before pixelation occurs.

What I'm trying to get at is PPI doesn't much matter. You need enough total data to be able to see whatever it is on the slide that you're trying to see.

I don't want to pay for 30 to 40 times the cost for storage if I don't have too

How many lectures do you attend? How many slides do you shoot?

Assuming the full RAW resolution of a 5Dmk4 at 40MB, it'd take you 25,000 images to fill a Terabyte, a Seagate 1TB Barracuda at the time of this writing goes for $65 retail, or $.0026/RAW image.

Add to this the fact that you won't be shooting RAW but will be shooting or converting to JPG for long term storage and the number get even more in your favor.

I really don't understand cost as an argument here.

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  • I guess I was thinking not just in lectures but in photo image sizes as well. So for me, the cost is also the cloud storage costs. AWS S3 pricing (aws.amazon.com/s3/pricing) is $150 to $276 per year for a terabyte (1000G x $0.023 per GB/mo * 12mo = $276). The benefit of using AWS is that I don't have to copy the data to a new drive every 5-8 years when the drives fail. So if I could spend only $9.20/year instead of $276/year, I'd prefer that. The $9.20 is based on $276/30 = $9.20. Over 10 years that's $2,760 vs $92.00. – PatS Dec 17 '19 at 1:08
  • @PatS if you don't have need to access the files on a daily basis then the cost of cloud hosting is really expensive for a simply archival solution. There are many different physical media you can choose from for archiving these images. Make 2 copies - one you keep locally and one you keep in a safe deposit or other secure location. – OnBreak. Dec 17 '19 at 4:51
  • Have you done this (safe deposit box)? The problem I had with it, was that my images were created daily, weekly, monthly and the remote archive was always missing data. I tried it once. :-) Then I realized I wouldn't keep up with it. So I try to keep the files small so I can mirror remotely. I've used SpiderOak, Dropbox, and Microsoft OneDrive (and multiple Terabyte portable drives). For me the easiest thing is to have my local photos mirrored to say Drobox. – PatS Dec 17 '19 at 5:38
  • @PatS I have every image stored locally on a RAID setup that is copied to a low tier dropbox account. These are for working files. When I'm done with them, I move them to a local but separate HDD for medium term access while prepping full BD-R sized folders. When I've amassed another BD-R's worth, I burn two discs and scrub the files from dropbox. One disc stays with me, the other goes to offsite storage. End of day, the images are onsite on BD-R + HDD and offsite on BD-R. – OnBreak. Dec 17 '19 at 6:15
  • I still don't get your argument. Either you pay ridiculously for cloud storage and its ease of use and access or you do what you need to do for a system like mine. Refusing to make time for a good archiving solution and then complaining about cloud costs is, to be frank, pissing into the wind. – OnBreak. Dec 17 '19 at 6:17

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