Large images are one of the most common reasons web pages load slowly, emails bounce, and upload forms reject files. A photo straight from a modern phone can be 3–8 MB, yet a version that looks identical on screen can often be a few hundred kilobytes. Getting there is mostly about two decisions: the right dimensions and the right format and quality. This guide explains both.
Step 1: Resize Before You Compress
Dimensions matter more than any compression setting. A 4000 × 3000 pixel photo has 12 million pixels. If it will be shown at 1200 pixels wide on a website, three quarters of those pixels are wasted. Reducing it to 1200 × 900 cuts the pixel count by more than 90% before compression even starts.
Useful target widths:
- Full-width website images: 1600–2000 px (to stay sharp on high-resolution screens)
- Blog or article images: 1200 px
- Thumbnails and product grids: 400–600 px
- Email attachments to view on screen: 1600 px is usually plenty
Use the Image Resizer to set exact dimensions, then compress the result.
Step 2: Choose the Right Format
| Format | Use it for | Avoid it for |
|---|---|---|
| JPEG | Photos and images with smooth gradients | Logos, screenshots with text, anything needing transparency |
| PNG | Screenshots, diagrams, logos, images with transparency | Large photos, where files become very big |
| WebP | Website images of almost any kind | Very old software that cannot open it |
WebP is supported by all modern browsers and typically produces smaller files than JPEG or PNG at similar visual quality, which makes it a strong default for websites. For images you will send to other people or print, JPEG and PNG remain the most compatible choices.
Step 3: Pick a Quality Setting
JPEG and WebP use a quality setting, usually shown as a percentage. Higher quality means a larger file. The relationship is not linear: dropping from 100% to 80% often halves the file size with little visible difference, while going from 60% to 40% saves less and starts to show artefacts.
- 80–85%: A safe default for photos. Differences are very hard to spot.
- 70–75%: Good for web images where speed matters most.
- Below 60%: Expect visible blockiness around edges and in skies.
PNG is lossless, so it has no quality setting in the same sense. Saving a photo as PNG usually makes it bigger, not smaller.
How the ToolGhost Image Compressor Works
The Image Compressor re-encodes your image in your browser using a quality slider from 10% to 100% and lets you choose JPEG, PNG, or WebP output. You can see the original and new file sizes side by side and adjust the slider until you find the balance you want. Because processing happens on your device, your photos are never uploaded.
One useful side effect: re-encoding an image this way does not carry over the original file's hidden metadata (EXIF data), which can include the camera model and GPS location where a photo was taken. That is a privacy benefit when sharing photos publicly, but it also means you should keep your original if you need that information.
Checking the Result
- View the compressed image at 100% zoom, not just as a thumbnail.
- Look at areas that show compression first: skies, skin tones, fine text, and sharp edges.
- Compare file sizes. If a small change in quality barely changes the size, go back to the higher quality.
- Keep the original in case you need a higher-quality version later.
Why It Matters for Websites
Page speed affects both visitors and search rankings. Google's Core Web Vitals include Largest Contentful Paint, which measures how quickly the main content, often a hero image, appears. Oversized images are one of the most common reasons for a poor score. Beyond compression, websites can help by:
- Setting width and height attributes on images so the layout does not jump while loading.
- Lazy-loading images further down the page.
- Serving smaller images to mobile devices.
- Writing descriptive alt text, which helps accessibility and image search.
Common Mistakes
- Compressing an already-compressed JPEG repeatedly: Each save loses more detail. Always start from the original.
- Using PNG for photos: It preserves every pixel exactly, which produces unnecessarily large files.
- Using JPEG for screenshots with text: Text edges become fuzzy. PNG or WebP keeps them crisp.
- Skipping the resize step: Compression alone cannot compete with removing unneeded pixels.
Frequently Asked Questions
Why did my PNG get bigger after converting it?
If the source was a JPEG photo, saving it as PNG stores every pixel losslessly, which takes more space. Use JPEG or WebP for photos.
Does compressing an image reduce its resolution?
No. Compression keeps the same pixel dimensions and reduces the data used to store them. Resolution only changes if you resize the image.
What size should images be for email?
For viewing on screen, 1600 px on the long side at around 80% JPEG quality usually produces files well under 1 MB each.
Is it safe to compress personal photos online?
With ToolGhost, yes: images are processed in your browser and not uploaded. With other services, check whether files are sent to a server and how long they are kept.