Seeing Is Believing! MrSID vs. JPEG in an Image Compression Comparison

Glen Thompson
January 4, 2019
3 min read

Are you filling up your phone or computer hard drive with high resolution imagery? With today's high resolution digital cameras and mobile phones, it doesn't take long. The reality of how much space your pictures are taking can be quite eye-opening. And the issue is only going to get worse as camera manufacturers continue to create higher resolution imagery. While the cost of computer storage is slowly decreasing, it’s not decreasing at the same rate that the size of digital imagery is increasing, so what are you going to do? The answer is image compression.

But that answer leads to a choice. There are two types of image compression: lossless and lossy compression. Lossless compression compresses the information in such a way that maintains all of the image information and as a result there is no loss to the quality of the image. Lossy compression, however, modifies the data allowing for even smaller compression sizes but with a loss of image quality.

The JPEG file format is an industry standard lossy compression algorithm familiar to us all. Typical JPEG-compressed images have a filesize reduction of around 1/10th of the raw image size. This compression comes with a loss of image quality, with no way to regain that quality. If you care about the fidelity of the original image, what choice do you have besides the lossy compression of JPEG?

New to the creative market is the MrSID file format. MrSID has been the industry standard image compression algorithm in the GIS market place for over 20 years. It’s available in SquishPic, Extensis Portfolio, as well as GeoExpress, Express Server and GeoViewer. This file format does both lossless and lossy compression for whatever your needs might be. If you need to preserve image quality, MrSID allows you to reduce the filesizes dramatically. If quality loss is acceptable, however, that is where MrSID shines when compared to the JPEG file format.

How do we measure loss of quality between image compression algorithms? With lossy compression you are changing the data from the original values. Measuring this "change" in data from the original is a common technique, which we will display for this comparison. A common measurement used to compare compression algorithms is called an MSE which stands for Mean Square Error. This measures the "error" in the lossy compression. The original value is X and the new value is Y. There is measurable error, or difference, between the original and compressed data. Let’s look at the measurable error MSE and compare JPEG to MrSID.

In the following table we are displaying some image information along with their corresponding error. The files are the same physical size and have different "error/MSE" values. The MSE values for the MrSID files are smaller than the values of the JPEG file of the same size. This tells us that the MrSID files has less error of the JPEG files of the same size, indicating the amount of loss is less.

JPEG Quality:
10
SID Compression Ratio
130
RAW Uncompressed Image
Filesize:
6034
Filesize:
6031 size difference -3
Filesize:
786432
MSE:
109.1146
58.28732
138.3505
MSE:
62.83893
43.36351
73.56931
 
SUM MSE:
305.75242
SUM MSE:
179.77175
 

 

You can see the difference in the images themselves. The MrSID images look better—less pixelated—than the JPEG of the same file size. For me, it’s pretty easy to identify that the MrSID has the superior image quality compared to the JPEG of the same size.

So there you have it. MrSID is a powerful image compression algorithm that supports both lossless and lossy image compression. Moreover, in a side-by-side comparison of lossy image compression with JPEG, MrSID is clearly the winner as you can see. But don’t take our word for it, give it a try and see for yourselves.

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GlenThompsonGlen Thompson – QA Manager of GeoExpress, Express Server, GeoViewer and SquishPic

Glen has been doing QA for the last 20 years and is very passionate about it. He sets the bar very high for himself and strives for perfection. He loves working with imagery and LiDAR data, and looks forward to new and exciting technologies. When he's not working, Glen enjoys spending time with his wife and daughter riding dirt-bike motorcycles, playing golf and playing video games in Virtual Reality--his latest hobby.

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