I think that is a good suggestion
meadow_wind; to add that
information to the welcome section - so that new members can learn to understand that slimming down images here at the forum is highly welcome, contributing to smoother browsing experience / avoiding a slow down a thread to load.
Using a computer like you do, does indeed make things a lot easier; to compress images in for example Photoshop [-> File -> Export -> "Save for Web (legacy)" ] or though a wealth of other apps, which can do similarly.
Graphics
often (but not always) get the smallest file size when saving them in GIF or 8-bit PNG's. Those two formats actually preserve the quality of graphs, while maintaining small file sizes (as long not too many details are present in the graph). The very strongly compressed JPG on the other hand, creates fuzzy lines, where colors start to "bleed", smooth tones get "stripy".
Yet, even a slightly fuzzy graph, can be good enough to read at the forum - so, perhaps it really that crucial - yet good to know what does what.
First is a PNG-8 while the second illustration shows 25% JPG compression. Notice how fuzzy the strong JPG compression affects the quality of the graph.
GIF file: 64 kb | PNG-8 file: 32 kb | PNG-24 file: 98 kb | JPG 90% file: 140 kb | JPG 25% file: 34 kb |
Actions in Photoshop
When i resize a photo that is let's say 2500 pixels wide, you can create "Actions" (In which you "record" a set of steps, which henceforth will be executed automatically every time you push an "Action" button)
It allows me for example to resize any photo down to either 1200 pixels or (700 px if it is a vertical photo) - while also adding a white frame around it with a thin darker line to make it look nicer. Those things can be beautifully done in Photoshop and help, when you deal with many photos without having to repeat every step manually over and over again.
Compressions
There is no rule how much or little to compress. For images I like to upload to the forum, i try to avoid that it degrades too much visually, while keeping an eye on the desired filesize (I try to keep it below 150 kb or 0.15 MB) When using an already strong compressed image from the internet, then it doesn't really matter that the compression is strong (but will still keep the already small size small).
Naturally, strong(er) compressions should only be used when posting something
online - but not for storing good photos in your private library - because compression throws away image info, that you never can get back (for example when you wish to change an image in terms of color balance, contrast, etc - which doesn't work well with too compressed images).
Screendumps / Screenshots
The reason that PNG screenshots are to heavy in file size - is twofold:
Everything is saved as 24-bit PNG (higher bit density) file - but at the same time also creates large dimensions (Read; much larger than what is needed here at the forum) The dimensions from one screen dump test on my iPhone - which dependent on your mobile phone's actually screen size - results into 1284 x 2772 pixels (= 3.6 MB) file. Albeit my iPhone says in this case - its a 8.4 MB file !
That's a lot.
So, why are mobile phones doing this ?
Well, because the modern screens are often made with very high resolution (many pixels). In the Apple world it is called "Retina". In order to achieve that crispy (non-jagged) look on screen, a screenshot (or photo or anything you look at) - everything is (in reality) much larger in dimensions. It is like you take a huge photo, press it into a smaller surface - but on a high very resolution screen, that photo looks unusual crisp and detailed. Therefore the screenshots you make, are much larger in both size as well dimension.