10 Common Mistakes When Compressing Images and How to Avoid Them

Introduction

Product photo from a few years back that still bothers me. Customer saw it and thought we were selling a blurry version of the item. We weren't. Cranked the quality way down. Didn't realise how bad it looked until the emails started.

That wasn't the only one. Blog post where every image looked shot through frosted glass. Another time I overwrote the original file. Nothing to fall back on. Just gone.

Now I run through the same mental checklist every time I touch an image. Writing it out so you don't have to learn this the hard way.

Compressing Too Aggressively

Slider goes zero to a hundred, you think lower is better. Wrong.

Quality falls off a cliff at some point. Photo at 30 percent might look fine in a thumbnail. Zoom in and you get blocky artefacts, smeared details, colours bleeding into each other.

Stick to around 80 percent. Going lower? Test at full size first. Image Compressor on Moon Tools Hub shows file size updating while you move the slider. Easier to eyeball it that way.

Ignoring Dimensions, Using the Wrong Format

Two mistakes that often go together.

First, dimensions. Photo that's 4000 pixels wide but displays at 800 on your site is carrying 3200 pixels of pure waste. Resizing does more for file size than any amount of compression ever could. Check before you compress. Resize to what you actually need.

Second, format. JPG for photographs. PNG for graphics, logos, transparency. WebP does both well. Compressing a photo as PNG and you end up with a file much larger than it needs to be. Compressing a logo as JPG and you get artefacts around the edges. Unsure? WebP is a safe bet for almost anything on the web.

Forgetting to Keep the Original

Hurts most because it's permanent.

Compress an image and the discarded data is gone. Overwrite the original with the compressed version and later need higher quality? Out of luck.

Learned this with a client project. Compressed a batch, saved over the originals, client asked for larger versions for print. Had to go back to the photographer. Embarrassing.

Always keep a backup. Work on a copy. That's it.

Not Previewing Before Saving

Five seconds to preview. Five seconds.

People skip it. Blurry images end up on their sites. Then they wonder what went wrong.

Used to be guilty of this too. Compress a batch, upload, notice days later something looked off. By then, redo the whole thing.

Look at the compressed image at full size before saving. Zoom in. Something off? Adjust and try again.

Compressing Already Compressed Images

Generational loss. Real problem with JPG.

Every pass loses a bit of quality. Do it repeatedly and damage adds up fast. Image doesn't just get smaller, it gets visibly worse each time.

Start from the highest quality version you have. That's the whole fix.

Auto-Compress Tools Without Control

Some tools handle compression automatically. Upload, they do their thing, you get a result. No control over how much compression happens.

Used tools that turned a good photo into a pixelated mess because their "smart" algorithm decided that's what I wanted. Used others that barely reduced file size. Frustrating either way.

Use something with a slider. You decide, not some invisible algorithm.

Not Compressing at All

Opposite mistake. People so afraid of losing quality they never compress anything. Storage fills up, pages load slow.

Get it. Was there once.

With careful settings you can reduce file sizes dramatically while keeping visual quality essentially unchanged. Start around 80 percent. Compare side by side with the original if you're nervous. Put them side by side. Bet you can't.

Using PNG for Photographs, Not Testing on Display Size

Two more that I still see constantly.

PNG for photographs is a bad idea. Lossless compression doesn't discard data, so for images with millions of subtle colour variations, PNG files become enormous. Can end up ten times larger than the equivalent JPG. Compressing a photograph, use JPG or WebP.

Testing on display size is the one I forget myself. Compress an image, look at it on my desktop monitor, think it's fine. Then see it on a phone and realise it's too small, or too large, or the quality was worse than I thought. Images look different depending on screen size. Sharp on a large monitor might look blurry on a high-res phone. Test on the devices where they'll actually be viewed.

FAQs

Most important thing to remember?

Keep the original.

How do I know if I've compressed too much?

Zoom to 100 percent. Blocky areas, smeared details, colour banding. Any of those, too far.

Same settings for every image?

No. Photos, graphics, screenshots behave differently.

Resize or compress first?

Resize first.

Does Moon Tools Hub store my compressed images?

No. Everything happens in your browser.

Final Thoughts

Compressing images well is a skill. Improves with practice.

Slow down a little. Resize. Pick the right format. Set quality carefully. Preview. Keep the original safe.

Do those consistently and you'll be producing clean optimised images without thinking about it.

Want to try this right now? Head to the Image Compressor on Moon Tools Hub. Upload an image, mess with the settings, see the difference.

Few times through and it becomes second nature.

Posted in: Image Tools