UKC

I'm doing am illustrated talk and wanted to have the opening shot display a map (of Canada).
It obviously needs to be about 2mb in size.

I'm using a Mac, I've tried copying, 'saving as....." and so on but with little success. Copying simply keeps it on the screen but I can't then see a way of getting 'info' which will let me see whether the saved image is big enough.

I've seen a few illustrated talks where the speaker has a nice map. Failing that I could simply photo a map and project that. But is that the only way?

In reply to Dave Perry:

http://commons.wikimedia.org/wiki/File:Canada_relief_map_public_domain.png

Most or all of the images on wikipedia are supposed to be public domain.

In reply to Dave Perry: Are you sure it needs to be 2mb that sounds absolutely massive (to me) for projection purposes

In reply to Dave Perry:
I don't know if it meets your needs but you can "copy" from Google Earth. Bring the map area you need into your screen Then >>File >>Save >>Save Image. It will then be saved as a JPEG.

Hope this helps.

In reply to Dave Perry:

I've given a couple of illustrated talks before and was led to believe that 2mb was a decent image.

That said thanks to Elsewhere I have an excellent 4mb picture of Canada for my talk.

However, all the information given is greatly received and anything else received will be perused.

Out of intereast Obi, how big is 'normal'?
And thanks mypryex too, I didn't know it got saved as a jpeg file.

In reply to Dave Perry:

if you search for images in Google, at the top of the search results is a bar which says "web, images, videos" etc. click on "images" and then click on "search tools" which will give you another menu. click on "size" and select "larger than" and you can select only images larger than 2MP.

You don't need the resolution to be as high as you might think for projections because, although the screen is larger, people are sitting further away.

In reply to Bob Hughes:

Another gem I didn't know. Thanks Bob.

In reply to obi-wan nick b:


Well, assuming it's a 24-bit RGB image (i.e. 3 bytes per pixel), that 2MB gives us 666kpixels in the image.

Assuming it's a 4:3 aspect ratio, that gives us an image 942 x 707 pixels.

If it's a 16:9 widescreen, then that would be 1088 x 612 pixels.

So not that enormous, given the likely resolution of the projector. A full HD projector, for example, has a resolution of 1920 x 1080 pixels, so your 2MB image would occupy about a third of the screen area.

There's not much point in inserting an image of a greater resolution than the intended display 'device'. That goes for web images, printed images and projected images.

In reply to captain paranoia:

You need to get the size right for your projector (and at 72 or 96 ppi) and then compress as a jpeg. Should be very acceptable quality at a lot less than 2MB.

In reply to Dave Perry:

Being an amateur at digital projectors I suppose my main worry or concern was that the picture would project too small - I assume I'm correct now in assuming that the size of the projected image will be the same even if the number of pixels or the mb size is less?

In reply to Dave Perry:

The number of pixels have to stay the same, but you can compress the amount of memory required to store that considerably in a jpeg. Tip: never compress a jpeg (that's already compressed) - always make it from the original, trying different quality settings.

In reply to Dave Perry:

You might be interested to know that, for A/V presentations to people like Rotary Clubs etc I now prepare a dvd and ask them to provide a dvd player/screen.

In reply to Gordon Stainforth:

Yuck, why on earth would you compress as a jpeg? You'd want to save as PNG. Compressing a Jpeg will just flatten the image and make it even more shit.

In reply to Removed User:

You may well be right. It's quite a few months since I last constructed a talk. I've a hunch you're right and that I used pngs for all my images. Certainly, though, the less memory you use, the smoother the show goes. (You wait for that red light to turn green if you use Apple Keynote)

In reply to Dave Perry:

I will be using a club's projector. And last time I used it I had all my pictures ready to go on a disc. I was even provided with an operator. "Next one Fred...."

My worry about vastly different projected sizes stems from when i gave a talk using my own digital pictures - which would have varied in size and quality somewhat, a couple I'd borrowed off the internet were absolutely crap - by crap I mean far too small when projected onto the screen to be seen by anyone further than the front row!! Even though I assume all my own images were of slightly different sizes (pixles & mb) when projected they appeared on the screen all exactly the same size - which makes slightly more pleasant viewing.

Hopefully, I'm only going to be using my own images this time (lesson learned), but some of the ones I want to use are only 1mb and I thought that if I projected a 1mb image it'd be half the projected size of a 2mb image?

In reply to Gordon Stainforth:


Dots per inch only has meaning when talking about a particular physical format display medium; a monitor screen of given physical and pixel dimensions, or printed page with given image physical dimensions. It has no meaning for a digital image (until that image is displayed). I'm sure I've tried to make this point before... ah yes, 8 Sept 2003....

I can take an HD image (1920 x 1080 pixels) and print it on a stamp (with a suitable printing technology; about 2000dpi), or project it on to the side of a building with an HD resolution projector. The visible dpi of these cases would be very different, but the image resolution would remain constant; that of the pixel dimensions of the image.

For the case of a projected image, we need to consider the resolution of the projector; if it can only display a VGA image (i.e. its pixel dimensions are 640x480), there's not much point in using images larger than VGA, since the additional detail cannot be displayed by the projector, and it will only be resampled away. And you're not in control of that resampling, since it's done by the page renderer of whatever tool you're using for your presentation.

On the other hand, if we take an image with a small pixel size (low resolution), and force it to fill a larger pixel dimension (high resolution) screen, each of the source image pixels must be scaled up to fill multiple pixels in the display screen, but giving a blocky appearance.

Strictly, when we talk about resolution, we ought to bear in mind the visual acuity of the eye, which is about 0.5 to 1 minute of arc. So, find the distance between eye and displayed image, calculate the angle each pixel subtends, and, if it's better (smaller) than the visual acuity of the eye, that will be as good an image resolution as you need... Unsurprisingly, the eye's visual acuity, which is determined by the cone density in the fovea, is pretty close to that determined by the Rayleigh criterion for the eye's lens; nature has optimally adapted the eye so the the sense elements are no smaller than the resolution of the optical lens system in front of it.

As for my comments about image sizes last night, I don't know what I was thinking, as I completely neglected the possibility that the image was compressed. And since I've worked on motion JPEG video compression systems in the past, that's a bit of an oversight...

JPEG is lossy, yes. But the degree of loss depends on the quality factor (level of compression). The higher the quality factor, the more image detail will be retained. Image size depends on pixel dimensions of the image, on image complexity (or detail), and on the quality factor. So a JPEG image of a white sheet will be quite small (no detail), whereas a JPEG image of a bed of moss could be quite large (lots of fine detail).

If you start with a raw RGB image, I'd first re-size (scale) the image using a decent resampling filter to fit 1:1 in the allocated image area of the display space (so, if you're going to allocate 1000x500 pixels on the page for the image, scale & crop the image to 1000x500 pixels). Only then would I compress. And I'd play with the JPEG quality factor until I was happy with the image quality and size (sometimes you are limited on the data size of an image). Or use PNG's lossless compression and accept the larger data size.

In reply to Dave Perry:

I wished I'd taken some slide film with me - it was much simpler .................However:-

One more question from me:-

If my memory served me correct last time I did a talk some years ago I put the pictures on a disc or usb stick and they were automatically projected in the order I put them on the disc. But I seem to recall once they were on the disc I was unable to alter the order they were shown in.

Is there anyway I can alter the order after I have the majority on the disc or usb stick?

In reply to Dave Perry:

Choose a smaller country...solved!

In reply to captain paranoia:

Well, OK - I know the pixel dimensions are all important (usually, I see from my notes, I set up for 1024 x 768 projectors). But since all pictures are prepared first on my computer, before being put into keynote, I've always found it simplest to treat them just like images for the web, and reduced in Photoshop, from the master, to those dimensions. Then 'Saved for the web' as a jpeg. Of course there's always a compromise re quality, but anyone who's seen any of my presentations will know that the pictures always look pretty good. There is always a problem with the overall file size, and movies are always a problem (you just have to keep talking for about 20 secs sometimes before changing to the next page, waiting for that green light!)

Of course the whole thing's a luxurious doddle compared to giving a medium-format slide show with my old Hasselblad projector. Those would take days to prepare, as every slide had to be glass mounted. Every slide involving 6 sides having to be cleaned of every minutest trace of dust. (The two sides of the film, and both sides of both pieces of glass.) Then the whole thing weighed a ton.