File Size Restriction

[MissDirections]

Hi.

I am planning to get some photos printed on vinyl wallpaper. The physical dimensions of the wall paper will be 1300mm x 2500mm and as I am ordering it online, there is an upload restriction of 8MB (file formats allowed are .pdf .jpg and .zip).

I would like to collage multiple images to create my wallpaper and plan to resize and edit each image before collating them in one large image. Then I will resize that image to be the final one (if that makes sense).

What I want to know is, is there any simple way to work out what my final image's pixel width and height will need to be to fit the 8MB restriction? I have no idea what the printing dpi is, the website only indicates that images should be 'at least 4MB for good quality'...which means nothing.

Ideally I would like to work with a starting image with 4x or 16x the pixels so it resizes nicely...I just don't know where to start.

Any help would be greatly appreciated :-)

[Ego Eram Reputo]

This is a good question, so I'm going to take some time replying.

Most of the time, resolutions are referred to in inches, so I'm going to do a quick conversion of your image sizes:

1300mm x 2500mm = 51.2in x 98.4in

That was easy! We'll store this information for use a bit later in this post.

File formats:

You have .pdf .jpg and .zip to choose from. Zip is not a file format - it's a compression system. You use it to squeeze the excess out of a file or group of files. If your PDF or JPG is too large, you could compress it by zipping.

That leaves PDF and JPG. A quick non-scientific trial revealed that the JPG version of a random photo was in fact larger than a PDF created using the Paint.NET PDF plugin (found here: Im(age)PDF). 1280 x 960 pixels = 928.4kb PDF but was 1.1mb as a JPG at 100%. Really, there is only 10% in it, but the JPG could easily be reduced by dialing down the save quality.

That means you can use either file type (JPG is probably easier).

When preparing images for print its recommended to work as large as possible. Unfortunately in your case this will not be possible. We got your image size in inches earlier, let's look at how that translates into pixels at various print resolutions (DPI):

51.2in x 98.4in @ 100DPI = 5120px x 9840px

51.2in x 98.4in @ 200DPI = 10240px x 19680px

51.2in x 98.4in @ 300DPI = 15360px x 29520px

That's an awful lot of pixels even at the low resolution! If you try filling the smallest canvas with random images & save it as a JPG you could get a file 50mb in size!

In my demo trial I had to drop the quality slider down to 59% to get an image 5120px x 9840px down to 8mb. Zipping afterwards saved me another 2mb, so I could have made the quality a bit higher - maybe 75%.

So here's the rub: If you use a goodly sized canvas, you'll have to lose a lot of quality in order to get it down to 8mb.

If you start with a smaller canvas, the jpg quality can be proportionately higher in order to still come in under 8mb. At half the size I could save the image at 96% quality to get 7.9mb.

Zipping the final JPG will save you more size.

If it was me, I'd use the half sized canvas 2560px x 4920px, save work-in-progress files as PDN, then when finished save it as a JPG with the quality wound up as high as the filesize will allow - then ZIP it.

[MissDirections]

Thank you so much! I have been fiddling with numbers on paper all day trying to estimate what I'm in for.

Can't wait to go home and set up my canvas now!

[Ego Eram Reputo]

Glad I could help. Oh and welcome to the forum!

[Red ochre]

Hello MissDirections (good user name),

Good answer EER.

I hope the image is 51 inches wide and the actual strips of wall paper are smaller than that – or it could be a tricky job hanging it!

I, for one, would be interested to see how you get on and whether you are pleased with the results or not – perhaps you could report back when the project is up on the wall.

Good luck!

[MissDirections]

I can do that. I am being tricky though and planning to cut up the large sheet into smaller images, hence making the collage and needing to know the size before I piece it together. Works out much cheaper that way than getting the company which makes them to print each one separately.

The largest image will be 150cm wide by 60cm high. And the longest will be a strip 240cm high and 30cm wide, that one will run the full height of the wall.

I rent and can't hang large pieces easily, getting this printed and delivered will be less than $200 and it's removable so it seems like a pretty good solution :-)

[MissDirections]

After resizing and combining all my photographs to make the wall sized collage and sending it off, I was emailed by the company and told that if I wanted it cut up around each photo then I should send them individually or they would charge me for their time to create an outline layer.

So I was able to send each photo with it's original quality 4-8MB each.

Much happier with that.

It's in the 'printing queue' now.