RedEyedJedi

I recommend the courses from 7thseasonstudios.com
Jeremy explains things fully, with no repetitiveness, and straight to the point.
Hope that helped

See:
Macros
Macros Macros: Equations Macros: Layer Behaviour Batch Processing with Macros And also the help file about macros here.

Because Affinity doesn't have the simplify filter called Cutout, you have to get creative and the way you can do that is to use the Frequency Separation Filter to retain detail and using either median blur or a box blur, create blocks of colour in conjunction with the posterise adjustment filter.
You can make a swatch of the colours using the swatch from image option in the swatches panel.
Posterise Level was set to 4
Box Blur was set to 5

Photo by Kal Loftus on Unsplash
 
Barack_Obama_Hope_Poster.afpalette

Well, while cruising the www in my quest for information, I came across this... It is an online version of a very popular GIMP plugin called G'MIC and it look what it has under the Artistic section of its filters.

This is what it produced on default settings

The preview is a bit hit and miss so what you see isn't necessarily what you get but its close ish.

Here's a macro that creates an "Obama Hope Poster" from a photo. It uses a Posterize adjustment and a Gradient Map.
Note: it is a single "afmacro" file, not a library category. Import it into the Macros panel, not into the Library panel.
Obama Hope Poster.afmacro

Hi

This tutorial may help, although this video is different from what you're looking to do the concept would be the same. Taking a part of one image and adding it into another. 

You may need to lower the opacity setting on the new set of teeth to show a kind of before/after effect. 

I hope this helps.
J

An interesting simple exercise is to create a square document 1000px x 1000px add 100px black and white stripes vertically and export that file to a jpg. Now rotate those vertical stripes so they are horizontal and export to jpg again using the same settings.
The jpg with horizontal lines will have a smaller file size than the one with vertical lines, yet they both have the same content.
 

Set the file to 72DPI and the file size should be small enough to email if you export it to jpeg on high quality.

And if it is to big for email you can use this
https://wetransfer.com

Wallpapers for Macs typically are JPEG files. Apple includes several dozen high resolution wallpaper images in the /Library/Desktop Pictures folder at the 5120 x 2880 px image size. But even though they are all the same image size, they range in file size from over 26 MB down to a bit less than 3 MB.
The reason for this difference is JPEG uses lossy compression to reduce file size at the expense of reduced image quality. In this sense 'quality' means the amount of fine detail in the image -- removing more of it results in greater compression & thus smaller file sizes. A consequence of this is that images that do not have a lot of fine detail to begin with can be compressed to smaller file sizes more than images that do, even at the same relatively high quality settings.
So, the final file size of your wallpaper exported as a JPEG will depend on how many fine details it includes, as well as the export quality setting & its pixel dimensions. If you have access to a Mac, compare for example the Zebras.jpg to the Pink Forest.jpg file in the /Library/Desktop Pictures folder -- because the first has tons of fine detail while the second has very few of them, the second can be a much smaller file without significant loss of quality. You can take advantage of this by filling areas of your wallpaper with the same color, by applying a minor amount of blurring to soften edges, etc., but that will depend on the design of your wallpaper & how you want it to look.
Also note that on Macs the System Preferences > Desktop & Screensaver offers several different ways to fill the screen with the wallpaper image, so it is not always necessary to match the screen size & image size exactly. Because of this, the DPI of the exported JPEG doesn't matter much.

Thank you. i understand now 

I would just set new page size and scale objects as one, then look what should be done to aspect ratio... but that is the quick and dirty way. Most objects are vector and background is [image] so there should be no impact on quality.

The pixel image is resampled using whichever method you choose (what I outlined in cyan in my screenshot). A brief explanation of the available methods is buried in the Export help topic:

What R C-R requested points out several things. If the width only needs changing, you should be able to only resize the document, keeping the elements centered. If you want to re-position elements, constraints may be the way to go. Myself, have only used those a few times, but the feature appears to give extensive control over how any elements are positioned within the bounding area.
 

You can do this in Document Setup. Under the Dimensions tab, there is a section that says "Objects will," and by default, "Anchor to page" is selected. Switch to "Rescale," and then add in your new dimensions above that. Rather than just change the artboard size, it will change the size of the vector objects inside as well.

That method should work fine. Just make sure the width-height lock is open & set the width to 8 inches:

I suggest using the Lanczos algorithm for better quality in the background image file, & if you are picky, before doing this, make these minor changes:
1. Select the group that contains your converted text (third from the top in the Layers panel) & in the Stroke panel tick "Scale with object." That will apply that stoke setting to all the subgroups & their curves in one go.
2. Expand one of the 2 subgroups with your converted text so you can see the subgroup with the fx symbol, click on that symbol, & at the bottom of the window that opens, tick "Scale with object."
3. Do the same for the other subgroup with your converted text.
4. Select the top level rectangle, click on its fx symbol & (you guessed it!) tick "Scale with object" for it as well.
5. Now do Document > Dimensions, rescale as above & you should have an 8x3 inch document.
In the attached Trooper 8x3.afdesign file, I did all of the above except I forgot to do #4.  I included the history so you can see my steps.

On Windows, holding down the Ctrl key (equivalent to Cmd ⌘ on a Mac) makes the selected object(s) resize from the centre. The effect of the Shift key modifier will depend on your Preferences settings, but the default setting for ‘Move Tool Aspect Constrain’ makes objects with a natural aspect ratio (e.g. images) retain that aspect ratio unless the user holds down the Shift key.

Holding the shift key constrains the size for objects; not images. When you drag the corner for images, it is already being constrained without having to hold Shift - which makes sense since it would distort it. Is that what you're thinking?
You must be on Windows, because when I hold Ctrl and resize, objects and images scale and rotate.

Your welcome, I will probably work on something tomorrow 

I'll have to make a tutorial on creating a Menu in Affinity Publisher as there don't appear to be any around.

Yes Affinity Publisher is your best app