# How to span 1 Wallpaper across iMac 27" 2017 & External Display

Discussion in 'Design and Graphics' started by biniaz, Sep 23, 2017.

1. ### biniaz macrumors newbie

Joined:
Sep 19, 2017
Location:
London
#1
I have tried Multi Monitor Manager & other programs to do this but the image on the 23" AOC 1920x1080 is always off. I came across a thread here & tried to follow it but haven't been able to get this right.

My new iMac is 27" 2017 model which I have AOC 23" attached. I gather that the iMac is 5120x2880 and the AOC 1920x1080. I was advised to try to use Photoshop to do this with layers and boxes which would include the bezels but I haven't a clue how to do this. I have included the thread below - if anyone can advise that would be amazing. This is what Im trying to do and think I have the resolutions correct but may need help with that to confirm I have but mainly don't understand how to do this in Photoshop

#2

Hello! I currently have a 15" retina MBP with a 24" 1080p display as a second monitor. I would like to make a wallpaper that spans across both displays, with the bezels on each representing a break in the actual image. I am running into difficulties in making the image line up correctly across the displays.

Here is how I have my monitors laid out:
View attachment 643866

Resolutions for each:

rMBP: 2880x1800 (but I am currently running the "Default" setting, which "looks like 1440x900")
24" display: 1920x1080

Any help would be greatly appreciated. Thank you so much!!
Click to expand...
I was in your shoes a few years ago. The real trick is match the pixel density on each screen so that it really looks like each monitor is a window looking onto the scene. Some simple proportional math will help you with that. The effective pixel density of the retina display is (2880^2 + 1800^2)^(1/2)/15 = 226.4155 pixels per inch (ppi). The pixel density of the 24" display is (1920^2 + 1080^2)^(1/2)/24 = 91.7878 ppi.

You have to increase the size of the image you use on the 24" monitor to match the pixel density of the laptop screen. So the horizontal resolution of the image you need on the 24" monitor is 1920/91.7878*226.4155 = 4736. Similarly, the vertical resolution is 2664.

Now that you know the working pixel density (226.4155), you need to measure the width of the bezels in inches and then multiply by 226.4155 to know how much space in the image to allow for them. For example, if each bezel is 1/2-inch wide, then you have one inch or 226 pixels of gap between your images.

Now, use your favorite image editor that supports layers to make some boxes of the right pixel sizes to represent your laptop screen, the external monitor, and the bezels. Arrange these boxes on top of a large image for the wallpaper and save out the two images you will need for the wallpaper: one image for each display. This will allow the images to line up on both monitors. In your case, you will need a starting image of 2880 + 226 + 4736 = 7842 pixels wide and 2664 pixels tall.
--- Post Merged, Aug 8, 2016 ---
By the way, here is a link to some very large images you can get started with. http://osxdaily.com/2013/02/15/12-stunning-high-resolution-wallpapers/ If you already have images you want to do this with that are not large enough for full retina resolution, then divide your working pixel density in half (113.2078) and use the effective resolution of the retina display (1440x900) for your image size calculations.

2. Sep 23, 2017
Last edited: Sep 23, 2017

### jahala macrumors regular

Joined:
Feb 7, 2008
#2
Hi. I wrote the advice you quoted. I looked up the DPI for the 5K iMac and found it to be 218 dpi. I also calculated it for your 23" 1080p AOC monitor and it is 96 dpi. So for your AOC monitor, you want an image that is 1920/96*218=4360 pixels wide and 1080/96*218=2452 pixels tall. I will assume that the 23" monitor is either left or right of the iMac (not above or under).

This means that to take advantage of full resolution of the 5K iMac and have the lines "flow" from one monitor to the next properly, you need an image that about 10,000 pixels wide and 2880 pixels tall. iMac screen (5120) + AOC screen (4360) = 9480. You also need 218 more pixels of width for every inch of space between visible portions of the two screens.

I took a screenshot of my monitor layouts file in Pixelmator. You can see the various layers on the left. This one is set up for an 11" macbook air at 1366x768 (green), three 24" monitors at 1920x1080 (pink), or two 17" monitors at 1280x1024 (cyan). For the 24" monitors, the bezels and distance from laptop screen are represented by the orange boxes. The bezels of the 19" monitors are shown in pink.

So you make one box on each layer, arrange them properly and then bring in the wallpaper image as an underlay. Arrange it so you can see the parts you want on each monitor, then copy the appropriate region of the wallpaper image and paste into a new file. Those new files are the ones you use as the wallpaper on the iMac and the AOC. I hope that helps.

3. ### biniaz thread starter macrumors newbie

Joined:
Sep 19, 2017
Location:
London
#3
Wow. Thank you very much. I was a little out on my sums but had downloaded images that were above that size so I was on the right track.

The problem I have is with the image software. As I have Photoshop I have never used it to do something like this.

You are correct I have the iMac to the left and the AOC to the right
WOW. Thank you.

My sums were slightly out but I had downloaded images to use that were that large so was on the right track. You are correct I have the iMac to the left and the AOC to the right.

The problem I have is how to set this up in Photoshop as I have never used it for this and don't know what I'm doing with it. When I open up Photoshop what size do i start with and what do I do from there? I sometimes wish I wasn't so OCD with these things but I am & need everything in it's place and to look just right.

Is there anywhere on youtube or other sites that would explain this better to me regarding how to set these layers up? Or is Pixelmator easier to use to do this? I know my setup isn't going to change for years so once I have this done I don't need to worry plus I can set wallpapers for the kids on there sections of the computer.

Part of me wishes I had bought 2 iMacs lol would have made life so much easier!!!

4. ### jahala macrumors regular

Joined:
Feb 7, 2008
#4
Attached are two photos. One is the wallpaper before I prepared the images for each monitor. The other is how my monitors look after following my process.

5. ### biniaz thread starter macrumors newbie

Joined:
Sep 19, 2017
Location:
London
#5
Thats what I want
--- Post Merged, Sep 24, 2017 ---
I have even bought Multi Monitor Wallpaper app but it never lines up so when I saw your post I wanted to do the same but understand the sums behind it but can't put it into practice in the software
--- Post Merged, Sep 24, 2017 ---
Also can this be used in Windows 10 for the wallpapers there? On MacOS do I need to change Display Settings to Fill or Stretch or Scaled to Best for Retina Display?

6. ### jahala macrumors regular

Joined:
Feb 7, 2008
#6
I previously recommended you try to find images that were about 10,000 x 2880. That is your starting size in Photoshop.

Here is a link to a crash course on layers. I am not doing anything complicated with them. I just make one layer for each colored box that I need. That way I can manipulate them individually. It does not really matter which order the layers are in as long as the wallpaper image is on the bottom. I set all my colored box layers to 40% opacity so that I can see the wallpaper image underneath them.

I found this link that explains how to make a rectangle of a specific size in Photoshop. I hope it works for you. I don't have Photoshop so I cannot test it myself. Once you can create a new layer, set the opacity to less than 100%, and create rectangles of specific sizes, you are in business. Then it is just measuring and math.

The only thing to point out is that the layer with the wallpaper image should be the active one when you copy the region so you can paste into a new file and scale down to the monitor resolution. Then export to a JPG.

7. ### biniaz thread starter macrumors newbie

Joined:
Sep 19, 2017
Location:
London
#7
I have got Pixelmator now - Is it possible to get a template from you where all I need or others need to do is delete Layers or Monitors they don't need and change the sizes of those boxes or Layers to rep there monitors and setup? Then Underlay there image and copy out the layers they need?

8. ### jahala macrumors regular

Joined:
Feb 7, 2008
#8
If windows 10 will allow you to assign a different image to each display, then my technique will work. Apparently, there is hope. If you want to show one image spanning both screens and get the same effect, then you have to cut out the parts covered by bezels and empty space and then move the part that goes with AOC over next to the iMac part. I have tried this and found it difficult to get the break between monitors correct. I usually end up with one column of pixels on the wrong screen which drives me nuts.

9. ### biniaz thread starter macrumors newbie

Joined:
Sep 19, 2017
Location:
London
#9
It all drives me nuts if it's not just right lol

10. ### jahala macrumors regular

Joined:
Feb 7, 2008
#10
Excellent! Download the attached zip file and unzip it. It contains the layouts I showed above. Open it Pixelmator. You can use Edit->Canvas Size... to adjust the height and width of the canvas to 10000x2880. When you are ready for the wallpaper image, just drag it into the Pixelmator window.
--- Post Merged, Sep 24, 2017 ---
If you want to use Photoshop, you can export the Pixelmator file to a PSD that photoshop can open. The PSD is huge so I am not able to post it here.

File size:
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11. ### biniaz thread starter macrumors newbie

Joined:
Sep 19, 2017
Location:
London
#11
Thank you very much. Could I Private Msg you and ask something there also

Joined:
Feb 7, 2008
#12
Sure

13. ### jahala macrumors regular

Joined:
Feb 7, 2008
#13
For the wider audience, I made a video that shows how to use Pixelmator to make the wallpapers once you have figured out what size everything should be.

14. ### biniaz thread starter macrumors newbie

Joined:
Sep 19, 2017
Location:
London
#14
Amazing Video thanks. Just one question. When you do the 2nd monitor you didn't change the pixels size when you copied it in. It was still 4360x2352. Wouldn't you need to change that to 1920x1080 or that screen size?
--- Post Merged, Oct 7, 2017 ---
Also 218 I thought was the bezel gap? I put my res at 300 will change this.

Using smaller images than 10000x2880 would just mean black bars or pixelated image on the iMac is that correct?

15. ### jahala macrumors regular

Joined:
Feb 7, 2008
#15
Actually, the first time I did the video, I did make the image size for the second monitor 1920x1080, but after I pasted in the image I forgot to scale it down to fit so I wanted to make sure that did not happen to others. Of course you can do that if you want.

You are correct about what happens if your images are not large enough. You can scale down the layout template uniformly by any amount that allows you to work with smaller images, but the OS will scale them back up to fit your screen.

I would rather deal with the scaling myself in the beginning so I can try to mitigate it.

16. ### camomac macrumors 6502a

Joined:
Jan 26, 2005
Location:
Left Coast
#16
I really like this tread. Thanks for sharing.