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Reducing JPEG file sizes

Uluru_5

What is JPEG?

JPEG (Joint Photographic Expert Group) is one of the most common image file-types on the internet currently, chances are when you export a file using your photo editing software you are likely exporting to JPEG to then send to someone, put on Facebook and so on.  In order to balance file-sizes, JPEG offers the ability to adjust the degree of compression applied to an image which allows the user to make a trade-off between image size and the quality (that is the lower the quality, the smaller the size).

Typically, this is controlled at a very global level and when exporting a file the user would select the quality of the JPEG image (e.g. commonly 80%) however, this number may have an impact on quality of one image but not another (that is its not really an image aware number) this is where there are some specialist tools which are valuable for striking a balance between file size, and quality per image, auto-magically. The most common tool that I know of (and that I use) is called JPEGmini. This tool works by analyzing the image using a quality detector which mimics the human visual system, it then adjusts the compression to the maximum amount before compression might cause perceivable visual artifacts.

To show how much of a difference this can make, I exported a full resolution image of the picture below;

Uluru_5

Figure 1: The image that was exported, note this is a lower-resolution version just for an example.

 

What are the reductions in file-size, and are there quality impacts?

At full 100% resolution and quality, exported as JPEG this image had a file-size of 20.8 MB. When i ran it through JPEGmini Pro 3, it reduced the file-size by around 77% leading to a reduced file-size of 4.69 MB (around 16.9 MB reduced). Of course file-size is not all that matters, and in reality there is really no point in having reduced file-size images if it means that the quality is no longer acceptable. To show the difference between images, I have compared them both in Lightroom (below);

Figure 2: The after (left) and before image (right) showing the differences between images. Note: this is a thumbnail, full comparison image is about 4.65MB in size.

 

In the above example, it lead to a reduction of about 77% in the file-size of the image with no perceivable image degradation at typical magnifications. Now I am sure if you were pixel peeking you would likely see a difference at very high magnifications, and if you are printing larger scale it may not be as beneficial but for most purposes I think it shows fairly well how the software can reduce file-sizes without affecting quality. To see how the software would perform with other images, I exported nine (9) other landscape images at full resolution, 100% quality JPEG and recorded the initial file-size, before running each of the images through JPEGmini Pro 3 and calculating the reduction in file-size, the results are presented below;

 

ImageOriginal File-size (MB)Percentage Reduced
134.048%
24.962%
33.974%
42.664%
51.261%
61.865%
73.559%
814.576%
924.959%

 

The difference in percentage reduced IMHO is a good example of how image aware the software is, it is analyzing each image to work out how much it can reduce the quality without it affecting how people see the image. This means that the amount being reduced will often change between images (e.g. Image 1 was reduced far less than say Image 8). Having that ability to be image aware and set differing quality levels auto-magically is a huge time-saver!

 

So how do I use this in my workflow?

Since JPEGmini Pro incorporates into Lightroom Classic, I tend to use it automatically if I am exporting a JPEG image as a set-and-forget process. This means that each time I export a JPEG image (unless i turn it off) each image it automatically optimized to strike a balance between file-size and quality. If I am doing processing of images, I typically export as a TIFF or PSD file (which are not optimized by JPEGmini) and when I have finished I export the file as a JPEG (from say Affinity Photo) and then manually reduce the filesize in the JPEGmini Stand Alone Program.

 

So far I have only been using JPEGmini Pro 3 for less than a week, and it keeps track of the total amount you have saved as a result of optimization. In my case in less than a week I have saved 1.03 GB of space. I used JPEGmini Pro 2 prior to the latest update, and with that I had saved more than 35GB of space (not counting optimizing space on my work computer)

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