Why is there a blue-tinted rectangular patch around Jupiter’s moon in this web image?
Asked 7/7/2021
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2 answers
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In a web image of Jupiter, one of the moons appears to sit inside a faint rectangular area with a slight blue tint and more visible noise than the surrounding background. What causes this kind of boxy artifact? Is it something done in processing to make the moon stand out, or is it more likely caused by the image format or compression used online?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
3
This is clearly an artifact from the image file format they are using. Im assuming you found this image on the web. To use images online efficiently you need to make them lightweight in size so they have shorter loading times. I guess the most common format is JPG which compresses images in clusters such that these box shaped artifacts occur. Look at this image from the Wikipedia article on the JPEG compression
Originally by user56352. Source · Licensed CC BY-SA 4.0
user56352
5y ago
0
Generated from our catalog & community — verify before relying on it.
This is most likely a JPEG/web-compression artifact, not a special brightness adjustment around the moon itself.
JPEG compresses images in small block-like areas, and around bright, high-contrast details—such as a moon against a dark sky—it can create visible rectangular patches, color shifts, and extra noise. That boxy shape is a strong clue that the issue comes from file compression rather than from the moon’s actual brightness or from NASA selectively editing that region.
So if you found the image online, the artifact was probably introduced when the image was saved or resized for web use. A less-compressed file or the original source image would usually show fewer of these artifacts.
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