Compressing images for Slack messages

Getting a JPEG ready for Slack messages is mostly about two numbers: pixel width and file size.

There is no single magic number, but there is a sensible range for Slack messages.

Quality is the slider people touch first, yet it is often the least understood.

Reducing file size is a sequence, not a single click.

WebP is newer than JPEG and often smaller, but compatibility still matters.

Choosing the wrong format can make a file five times larger than it needs to be.

Resizing is the single biggest lever for file size.

A few habits cause most of the blurry or oversized images we see.

You do not need an app to shrink photos on an iPhone.

Android phones can compress images right in the browser.

On Windows, a browser-based compressor avoids installing extra software.

Mac users can compress JPEGs without opening Preview or Photoshop.

Strictly speaking, JPEG compression always discards something, but you can make the loss invisible.

When you have dozens of images, consistency matters as much as size.

If an upload keeps failing, the image is usually larger than it needs to be in more ways than one.

Run through this list before you upload.

Hitting an exact size limit is easier with a target-size compressor.

Yes, but how much depends on your settings.

Blurriness after compression usually comes from resizing too far, not from JPEG itself.

Photos carry hidden metadata such as camera model, date and sometimes GPS location.

Dimensions decide how sharp an image looks and how heavy it is.

JPEGs can be saved so they load top to bottom, or as a blurry preview that sharpens.

Colours that look vivid on your camera can look dull after upload if profiles are mishandled.

Speed is the most visible benefit of compression.

You do not need paid software to compress images well.

Screenshots behave differently from photos.

Scanned pages are often saved at very high resolution.

A repeatable workflow saves time and keeps results consistent.

The honest answer is: more than you think.

Image compression comes in two flavours.

Text inside photos, like signs or slides, needs a gentler touch.

Faces are where viewers notice compression first.

Product photos must look accurate because people judge the item by them.

Good file names help you, your team and search engines.

Many online compressors upload your images to a server. That is not always necessary.

Size limits are written in kilobytes and megabytes, and the units trip people up.

Aspect ratio is the shape of the image, and the wrong one leads to awkward crops.

iPhones save photos as HEIC by default, and not every site accepts it.

An upload error is frustrating when the message is vague.

Short on time? Here is the fastest route.