PSD - Original

The original image is a picture of my son from a few years ago taken with my older Canon T2i SLR camera. I've left it at its full size of 3456x5184 by disabling the RapidWeaver automatic scaling features. All images are the same dimension, the only differences are image format and compression.

Saved as a PSD with some basic color and contrast adjustments the file is 87.8MB.

However macOS Catalina also says this file is 100.9MB on disk. I honestly have no idea why. If anyone knows why some files on APFS disks in Catalina sometimes have two different sizes, please let me know.

But saved as an uncompressed PNG image the file is about 20MB. So this is the baseline that I'll use to measure all the compression.

Stacks Image 118

JPEG - Low Quality - High compression

This is the format you should probably use for large photos. Setting the quality somewhere in the mid-range is usually adequate for snapshots.

JPEG - 50%

1.3MB - Squash

94% File Size Reduction

Stacks Image 94

JPEG - 25%

696KB - Squash

97% File Size Reduction

Stacks Image 92

JPEG - High Quality - Low compression

JPEG is the most lossy, but setting the quality at 75% or higher often changes the image so little that it's difficult to notice. But be careful, each percent increase comes at a huge cost to file sizes.

JPEG - 100%

15.9MB - Squash

21% File Size Reduction

Stacks Image 76

JPEG - 75%

2.6MB - Squash

87% File Size Reduction

Stacks Image 78

PNG

Although lossless, for a large photo, the file sizes are prohibitively large.

PNG - Original

19.7MB - Photoshop

This is the full size image.

Stacks Image 64

PNG - Compressed

18.6MB - Squash

7% File Size Reduction

Stacks Image 66

GIF

Each image is limited to only 256 colors (from a much larger pallet of colors). This often radically affects images and for this reason GIF is not really used for photos. It's really best for little animated memes.

GIF - 256 Colors

1.6MB - Photoshop

92% File Size Reduction

Stacks Image 104

The limitations of GIF will affect different images differently. Pay attention to skin-tones in your images. Sometimes colors aren't chosen well and it can lead to sickly green or jaundiced people. Yuck.

GIF - 64 Colors

1.8MB - Photoshop

91% File Size Reduction

Stacks Image 106

Substantial image degradation. And the file size is larger than the 256 color image. Lower quality doesn't always mean smaller size.