Image properties for social media?

Question

My experience of social media is extremely limited, but I have occasionally been asked by a group to send them an image for use on their media. Sometimes as non-technical people only used to mobile phone images they have failed to upload the pictures or butchered them in an effort to do so.
In darktable I have presets that I use for exporting files for different uses.
The settings I can imagine include (there may be more):

1. pixel dimensions (ppi, file size)
2. file type (png, jpg, tiff, etc)
3. compression level (for smaller file size and less chance of reproductions)
4. colour profile (sRGB, AdobeRGB, etc)
5. styles (for adding modules to the pipeline - perhaps a crop, watermark and border)

I was thinking along the lines of this guide for twitter which shows how the images are used, their aspect ratios and file size limits:

The ideal image size and aspect ratio are 1200px X 675px and 16:9, respectively. The maximum file size is 5MB for photos and animated GIFs. You can go up to 15MB if you’re posting via their website.

You can tweet up to four images per post. Two images will appear stacked side by side, both with an aspect ratio of 7:8.

What settings are optimal / most useful for the various platforms?

Answer 1

None of 1-4 matter. All the major social networks (definitely including Facebook, Twitter and Instagram) re-encode any uploaded photos with their own settings, optimised for their use case (reducing file size/bandwidth) rather than yours. Obviously they can't re-add quality that wasn't there, but they can and will remove any carefully optimised settings you use.

Point 5 (styles) is much more a artistic decision than anything else; if you think your photos look better with a border, add a border - although again remember that the social networks often show a crop of the uploaded image in the main feed rather than the full image.

Answer 2

As mentioned in Philip's answer, sites will re-compress to their own standards, but you might as well start off with as good an image as they'll let you upload.

In brief:-

1. Pixel dimensions, whatever they ask for. DPI/PPI has zero relevance for on-screen display.

2. png if you need transparency, otherwise jpg.

3. Related to 1. If they have a file-size limit, set compression to land just inside it. May need trial & error.

4. sRGB for web/screen. Never trust any other profile to ever be accurately reproduced on random computers from random web sites in random browsers.

5. No style, unless they have a house style you must follow [if they do, also check if you must apply it or they will after upload.]. Watermarks are trivial to remove for anyone determined enough. See How to make the signature/watermark look better?

There is no "one size fits all" & each platform will have its own specification. You need to read their info & test all you will be using.
Also note that many sites use Responsive Design, meaning your image may be re-cropped on the fly to fit the viewer's screen, landscape or portrait.

Answer 3

I noticed that there was no mention of aspect ratios in the previous answers.

With Instagram, I've found that square or 4x5 (portrait) images tend to get better results because they fit within the platform's window better. Anything else is cropped and users have to go out of their way to view the entire image. There's some speculation that 4x5 images receive more attention as they do a better job of filling the screen on a mobile device.

I'm sure that there are similar strategies for Facebook and Twitter.