A phone photo is easily five megabytes or more. Attach three of them to an email, or put one on a web page, and the size starts to matter. The usual advice is to "compress the image", but that phrase hides two different things, and a third thing you may not know about travels in the same file: a block of hidden data that can include where you were standing. This article explains what makes an image file large, how to make it smaller without it looking worse, and what to check before you share a photo.
What makes an image file big
Three things decide the size of an image file.
The number of pixels. A photo that is 4000 pixels wide and 3000 tall has 12 million pixels. The same picture at 1600 by 1200 has 1.92 million, which is 16 percent as many. Fewer pixels means less to store, and on a normal screen you will often not see a difference, because a web page rarely shows a picture wider than a thousand or so pixels.
The format. JPEG, WebP and PNG store the same pixels in different ways. JPEG and WebP are lossy: they throw away detail that the eye is unlikely to miss. PNG is lossless: it keeps every pixel exactly, which is perfect for a screenshot with sharp text and a poor fit for a photograph.
The quality setting. For the lossy formats, a quality number controls how much detail is thrown away. Lower numbers give smaller files and, eventually, visible damage.
Resize first, then compress
The most effective step is usually the first one: make the picture the size it will actually be shown. A photo shown at 800 pixels wide on a page gains nothing from being stored at 4000. Shrinking the dimensions removes most of the data without touching the quality of what remains.
Then choose a format and quality. For photographs, a quality around 75 to 85 in JPEG or WebP is a sensible starting range: most pictures look the same as the original at normal viewing size while the file is far smaller. Go lower in steps and look at the result at the size it will be shown, not zoomed in. The point where smooth skies start to show blocks or banding is the point to stop.
Which format to pick
- Use JPEG for photographs that must open everywhere.
- Use WebP for photographs on the web when you control the page. It usually produces a smaller file than JPEG at similar quality and supports transparency, but a few older programs and upload forms still refuse it.
- Use PNG for screenshots, logos, diagrams and anything with flat colours and sharp edges. Do not use it for photos: the file will be much larger than a JPEG of the same picture.
Remember that lossy compression is not reversible, and it adds up. Every time you open a JPEG, change it and save it again, a little more detail is lost. Keep the original and always compress from it, rather than compressing a copy of a copy.
The part people forget: what a photo says about you
Cameras and phones write a block of information called EXIF into every photo. It normally contains the make and model of the device, the date and time, the exposure settings, a small embedded preview, and the direction the camera was held. If location services were on for the camera, it also contains GPS coordinates, often accurate to a few metres.
Editing programs can add more: XMP and IPTC blocks that carry captions, keywords and an author name, and a colour profile.
This is useful when you sort your own library. It is less welcome when the file leaves your hands. A picture of a parcel posted for sale can reveal the street you live on. A photo of a child sent to a group can reveal the school. Some websites and messaging apps remove this data when you upload, and some do not, and the rules change. Do not assume. A file attached to an email or sent as a document is normally delivered exactly as it is.
You can look at the data yourself. On a Mac, open the photo in Preview, choose Tools, then Show Inspector, and look at the Exif and GPS tabs. On Windows, right-click the file, choose Properties and open Details: the GPS section is listed there, and the same dialog has a link to remove properties and personal information. On an iPhone, the Share sheet has an Options button with a switch for Location.
Doing both in one pass
The image toolkit on this site handles resizing, compression, format conversion and removal of hidden data together, and it runs in your browser, so the photos are not uploaded. A typical sequence:
- Drop your photos on the box. The list shows each one at once with its current size.
- Choose "Set the width" and enter the width you need, for example 1600, or leave the size alone.
- Pick JPG or WebP and a quality, or keep the original format.
- Read the "Removed" line on each row. If a photo had GPS coordinates, they are listed with the word removed, so you can see exactly what you would otherwise have shared.
- Download single files or all of them as a ZIP.
The new file is created from the pixels alone, which is why the location, camera model, date and preview are not carried across. The colour profile is converted to standard sRGB so colours stay correct on ordinary screens, and the rotation your phone stored in a flag is applied to the pixels, so the photo is upright everywhere.
Common mistakes
- Compressing a screenshot to JPEG. Text becomes fuzzy. Keep PNG, or use WebP at a high quality.
- Enlarging a small picture to make it sharper. More pixels cannot add detail that was never captured. The tool never enlarges.
- Trusting a platform to clean the file. Remove the data yourself before you share, then check the result.
- Deleting the original. Lossy files cannot be restored. Keep the original photo and publish a copy.
A short checklist
Before you send or publish a photo: reduce it to the size it will be shown at, choose JPEG or WebP for photographs, start around quality 80 and lower it only while it still looks right, and make sure the location data is gone. That takes a few seconds per picture, and it protects both your bandwidth and your privacy.