JPGExtra – Sample JPG File
To demonstrate what JPGExtra does and why it's needed, let's look inside a typical JPG file to see the types of "extras" (or "metadata") and how JPGExtra can optimize such files by cleanly removing those extras.
Sample JPG File
This is a fairly typical photographic image that one might see on any website:
- File name: BushOrchids240x320.jpe
- Image size: 240 x 320 pixels
- File size: 41,314 bytes
The photo was taken with a digital camera and resized with Adobe Photoshop. The resulting image fits on a web page without scrolling and has sharp detail and good color.
The problem is not what we CAN see but what we CAN'T see. Let's take a peek inside the file...
Revealing What's Inside
Decoding the innards of the above sample JPG file reveals all sorts of "extras" (or "metadata"):
- JFIF Header: Small bit of data, mainly to indicate that the file is in traditional JFIF format.
- Exif data: Date and time of the original photo, shutter speed, aperture and other photographic settings, even the make and model of the camera.
- Thumbnail(s): Miniature version of the photo, which is used by some software for fast previews. Much smaller than the main image (only 96 x 128 pixels) and lower quality (note the "ripples"). The image editing software, Adobe Photoshop, adds two identical thumbnails. I've seen some JPG files with three!
- Photoshop data: Various other information added by Adobe Photoshop.
- Adobe XAP data: More info from Photoshop, this time in XML format, and often containing only 1/4 data and 3/4 blank space.
- ICC profile: Color profile for more accurate color rendition on different systems (eg. screens, printers). Ignore the actual "rainbow", which I added to show that this block has something to do with color.
- Adobe data: Tiny bit of additional data added by Adobe Photoshop.
- Main image: Finally, after all of the "extras", we reach the actual image data.
This JPG file contains about 44% of "extras", the bulk of which are downloaded and then simply discarded by most web browsers. It's a real waste!
Luckily, we can fix it, as shown below...
JPGExtra to the Rescue!
Here's the innards of the same JPG file after optimization with JPGExtra:
- JFIF Header: The header is still there, completely unchanged.
- Main image: The image is still there, completely unchanged.
- Extras? All of the extras (18,000 bytes!) have been cleanly removed.
On this sample, JPGExtra achieved savings of 44%, which is pretty impressive! Of course, I've ensured that the original JPG file contained a good selection of "extras", but it's a fairly realistic example.
On smaller images, even more impressive savings are common because the "extras" constitute a greater percentage of the