Question

How do scans saved as JPEG images (compressed and lossy) compare to scans saved as PNG images (compressed and lossless)?

Answer

There are several things to consider when instructing uScope Navigator to save scanned images as JPEG vs PNG.

Image Quality

JPEG images are compressed using a lossy compression algorithm. uScope Navigator saves JPEG images with a Q (quality) setting of 90 which achieves a good balance between image size and image quality. Nonetheless, at high levels of magnification, JPG artifacts are obvious.

PNG images are also compressed. However, they are done so that there is no loss of image data. Therefore, PNG image quality is always better than JPEG.

Image Size

Both JPEG and PNG images are compressed. However, the amount of compression depends on the content of the image. For example, an image that is a single color will likely compress much better as a PNG than as a JPEG. However, images with a lot of varied content will compress better as JPEG than as PNG. In general:

• JPEG images are compressed at a typical ratio of 14.3:1 at Q90.
• PNG images are compressed at a typical ratio of 2.7:1.

JPEG images output by uScope Navigator are most always smaller than PNG images. Typically, 5.3 times smaller, and this may be a consideration for systems with limited memory.

Image Speed

A common feature of whole slide images is that they are large. PNG images are larger than JPEG images. And, as such, they take more time to load, process, and render. Therefore, for a faster presentation experience, JPEG images are better.