Lossless photo compression, and what AccioPix actually does to your uploads
All photo services compress what you upload. Few tell you how. Here is our way. On a normal connection, photos uploaded to an AccioPix event keep their full resolution, every pixel you shot. A JPEG under about 3 MB that is already upright goes up untouched. The rest are re-encoded at high quality, so no difference shows at normal viewing size. The single exception, on a very slow connection, is explained below.
Lossless, near-lossless, lossy
Lossless photo compression saves the exact same pixels in fewer bytes. Lossy compression drops detail that the eye is unlikely to miss. Near-lossless is our name for the cautious end of lossy. The dimensions stay untouched. The re-encode is set high enough that you must compare both files at full zoom to tell them apart.
The field tracks that closeness with the structural similarity index of Wang, Bovik, Sheikh and Simoncelli (IEEE Transactions on Image Processing, 2004). The metric compares images by structure, just as vision does, instead of raw pixel error.
The upload, step by step
- Small, upright JPEGs go as they are. If the file is already under about 3 MB and needs no rotation, the uploader sends your original bytes. Nothing is re-encoded.
- Everything else is re-encoded in your browser. Your own computer re-encodes the picture before sending anything, starting at JPEG quality 95. It steps down only as far as needed to reach around 3 MB, and never below 85. Resizing is turned off. A 45-megapixel file stays 45 megapixels.
- Rotation is fixed. The camera's orientation tag is baked into the pixels. No viewer will ever display the photo sideways.
- Location is removed, camera details kept. The file keeps the capture time, camera, lens and exposure. That is how the album puts the photos in the order they were taken. The GPS position is cleared first, because album photos go to guests, and so are other blocks that can repeat it, such as XMP and IPTC, and the video tucked inside a motion photo.
- Colours stay true. An original sent as it is keeps its colour profile, Display P3 or Adobe RGB included. A re-encoded photo is converted to standard sRGB on the way, and labelled as sRGB, so no viewer over-saturates it.
- A small preview is created. Browsing the album uses an 800-pixel copy. Downloads and deliveries take the full-size file.
If the browser cannot handle the re-encode, the server takes over. It uses JPEG quality 90, progressive, with no resizing. That path drops the metadata completely.
The exception: very slow connections
The uploader checks the line. It looks for a very slow connection, a 2G network, a round trip over half a second or a download speed under 0.5 megabits a second. In those cases it asks you once whether to send 1,920-pixel copies of about 1 MB, so the work finishes. Nothing shrinks unless you say yes. Crowded venue Wi-Fi can trip that threshold.
HEIC and RAW
Your browser turns iPhone HEIC files into JPEG before upload. The server cannot decode HEIC. You can upload RAW files, but neither the browser nor the server can develop them. Instead, the uploader takes the full-size JPEG preview the camera embedded inside the RAW file. On most current cameras that preview has full resolution. Still, it is the camera's rendering, not your edit. Export your edited JPEGs when the look matters.
Originals stay with you
Use an AccioPix album to deliver photos, not to store them. Your originals, along with their full metadata, belong in your own storage. We only keep a full-resolution copy so you can share it.
The free tools work differently
We designed our free photo compressor for the opposite task. It makes files small for email, forms and websites. By default it uses a 2,048-pixel edge at quality 80, because size is the only goal there. The codecs belong to the same family, but with settings for another purpose. Read the guide on reducing photo size without losing quality.
Checking it yourself
Upload a photo, pull it back from the album, and compare them. On a normal connection, the dimensions match the original. Place both side by side at 100 per cent. Look at fine texture: hair, fabric, foliage. Any compression shows there first. It is the fairest test of photo compression quality you can run.
Frequently asked questions
Does AccioPix compress my photos?
Gently, and often not at all. Photos always keep their full resolution unless you choose smaller copies. A JPEG under about 3 MB that is already upright goes up exactly as you shot it. The rest are re-encoded at high quality to around 3 MB, so you cannot see the difference at normal viewing size.
What is lossless photo compression?
Lossless compression stores the exact pixels in fewer bytes. Nothing is thrown away. It saves less space than lossy compression, which cuts detail your eye is unlikely to notice.
Does AccioPix keep the photo's location data?
No. The GPS position is cleared before upload. We keep camera details like the capture time, lens, and exposure. This lets the album order the photos by when each shot was taken.
Can I upload RAW files?
Yes. The system pulls the full-size JPEG preview embedded in the RAW file. That shows the camera's rendering, not your edit. Upload your exported JPEGs if your edit matters.
References
- Wang, Z., Bovik, A. C., Sheikh, H. R. and Simoncelli, E. P., 2004. Image quality assessment: from error visibility to structural similarity. IEEE Transactions on Image Processing, 13(4), pp. 600-612.
Related reading
How to compress a whole shoot in your browser without uploading it anywhere, and how to stop WhatsApp from re-compressing your delivered photos.