Photo file size and format: the 5 MB upload limit

This page explains the numbers behind a photo file: what makes one photo file larger than another, how the iPhone's HEIC format compares with JPEG, and how to bring a pet photo under the 5 MB upload limit while keeping enough pixels for a print. The portrait studio takes one image file of up to 5 MB for each portrait, and a larger file gets the message "Please choose a photo under 5 MB." The main pet photo guide covers taking the photo itself.

Two sizes: megabytes and pixels

A photo has two sizes, and they are easy to mix up.

• Pixel size is how many tiny squares of colour make up the picture, counted across and down, for example 4,000 by 3,000 pixels. This decides how much detail the photo holds and how large it can be printed.
• File size is how much storage the photo takes, measured in megabytes (MB). The 5 MB upload limit is about this number.

The two are linked, but loosely. A photo with more pixels usually makes a larger file. The format and the amount of compression, the way the file packs the pixels into fewer bytes, change the file size too. Two photos with exactly the same pixel size can differ in megabytes by a large amount.

For a portrait, the pixels are what matter. The goal is a file under 5 MB that keeps as many pixels as it can, especially around your pet's face.

Why some photos are so large

Resolution settings

Newer phones can take photos with many millions of pixels. Apple says supported iPhones can switch the main camera's default resolution between 24 MP and 12 MP, where MP means megapixels, or millions of pixels, and can take 48 MP photos with Resolution Control turned on. More pixels make a larger file. Google says Pixel phones have a Full HD setting that lowers the resolution to save storage; the page on phone camera settings explains why to keep the higher setting for a pet photo and deal with the file size afterwards.

Format and compression

Encyclopaedia Britannica explains that the JPEG standard keeps files small by averaging colour variation and discarding what the human eye cannot see, a process called lossy compression. Britannica says an image can be compressed by a factor of 100 to 1, with some loss of quality at those limits, and that factors of 20 to 1 are easily done with a loss of quality that is practically invisible to the eye. It also says many digital cameras store images as JPEGs so more pictures fit on a memory card.

Apple says the iPhone 7 and later models, on iOS 11 or later, can capture photos in HEIF, the High Efficiency Image File Format. Apple calls the format HEIF; many apps, and the photo checker on this page, call these photos HEIC. Apple says HEIF offers better compression than JPEG, so photos use less storage on the device and in iCloud Photos while keeping the same visual quality.

Live Photos

Apple says a Live Photo records what happens 1.5 seconds before and after you take the picture. When you share, Apple says you can tap LIVE in the corner of the photo to send only the still image, and that a Live Photo sent by Mail arrives as a still. For an upload, the still photo is what you need.

HEIC and JPEG compared

Apple says that capturing in HEIF is recommended, and that the older formats are more broadly compatible with other devices and operating systems. It also says that when you share HEIF media by AirDrop, Messages or email to a device that does not support the format, the photo might be sent automatically in a more compatible format such as JPEG.

The photo checker on this page reads your photo in your browser. If your browser cannot open a HEIC file, the checker asks for an image such as a JPG, and exporting the photo as a JPEG solves it.

Converting HEIC to JPEG

Apple gives the steps for a Mac: open the HEIF image in Photos or Preview, choose File, then Export, then choose a format such as JPEG before saving. To make all new iPhone photos JPEGs, Apple says to open Settings, tap Camera, tap Formats, then tap Most Compatible.

Apple adds one more detail. When you import photos from an iPhone into Photos, Image Capture or a PC over a USB cable, they might be converted to JPEG. To stop that, Apple says to open Settings, tap Apps, tap Photos, and choose Keep Originals.

Bringing a photo under 5 MB

Try these in order. Each step keeps more of your pet's face than the next.

1. Crop away empty space

A photo of a pet on a large sofa has a lot of sofa in it. Cropping removes the parts you do not need and keeps every pixel of the face. Apple's guide to Preview on a Mac says you select the area you want to keep and discard the rest. Leave a margin around the ears and chin, as the page on camera height and angle explains, because a print may trim the edges.

2. Save as JPEG

If the photo is a large HEIC or PNG file, export it as a JPEG. Britannica's figure of 20 to 1 compression with practically invisible loss shows how much space JPEG can save.

3. Reduce the pixel size in small steps

If the file is still over 5 MB, reduce the pixel size. On a Mac, Apple says to open the image in Preview, choose Tools, then Adjust Size, select Resample image, and enter a smaller value in the Resolution field; Preview shows the new size at the bottom of the window. On Windows, Microsoft's free PowerToys includes Image Resizer: after installing it, you right-click an image in File Explorer and choose Resize with Image Resizer. Microsoft says sizes can be set in pixels, percent, inches or centimetres, and that the Fit option scales the image in proportion without cropping it.

Reduce in small steps and stop as soon as the file is under 5 MB. Every step down in pixels lowers the detail available for a large print.

Keep the original

Make the smaller copy as a new file and keep the full-size photo. A later print, or a second portrait, may need every pixel of the original. Apple says that in Preview you can undo a crop straight away with Edit, then Undo Crop, and that you can restore an earlier version later with File, then Revert To, then Browse All Versions. Microsoft's Image Resizer saves the resized picture as a new file, and its settings show an example in which a file named example.png becomes example (Small).png, so the original stays untouched.

How many pixels to keep

The pixels you keep decide how sharp a large print can be. Pixels per inch, or ppi, is the number of image pixels along each inch of the print. The four Purrealism print sizes are 8 × 10, 12 × 16, 18 × 24 and 24 × 36 inches, and the same photo gives fewer pixels per inch on each larger size.

The photo checker further down this page shows the pixels per inch your photo gives at each of the four print sizes, and puts each one in a band: 300 ppi or more, 150 to 299, or under 150. Run it on the photo before and after you shrink it, to see what the change costs. The guide to art prints and paper explains what these bands mean for a print.

What the photo checker shows about the file

The photo checker works in your browser, and the photo never leaves your device. For the file, it shows:

• The file size in MB, marked against the same 5 MB limit the portrait studio uses.
• The pixel width and height, with the pixels per inch at each print size.
• Brightness and sharpness scores, explained on the pages about black, white and two-tone coats and sharp pet photos.

A photo that passes the size check, keeps a high pixel count and shows your pet's eyes sharp is ready for the portrait studio.