Troubleshooting Photos –
Ragged Blocks Of Color In Photo, With Little DetailÂ
Problem
The color is uneven, with ragged blocks of color appearing in areas that should be smooth color. There are fringe effects around the edges of objects. Fine detail is missing.
What should you look for?
Look for the characteristics – known as artifacts – visible in the photos above and in the detail below. In areas of continuous color, look for obvious squares of color like those in the right side of the detail below. Around the edges of objects, there may be ragged lines where the tones change abruptly. There may also be a lack of subtle detail – look at the yellow stamen in the flower below, little more than a yellow blob in jpeg 3. See also the lines radiating out from the center of the flower – in jpeg 3, only the five major lines are visible, whereas in jpeg 60, hundreds of fine lines are visible, along with delicate gradations of color.
Note that the squares in these photos appear in areas of roughly continuous color and tone, or at the edges of changing colors or tones. In some photos, you may see squares that look like exaggerated versions of the detail that was present in a smaller version of the photo. These squares may appear because of poor choices when re-sizing a photo. See this page on resizing to be sure you recognize the difference.
This 250% detail from the photos above shows where the differences lie. Note the relatively crude blocks of color in jpeg 3, compared with the many tones flowing smoothly from one into another in jpeg 60. The blockiness of jpeg 3 jpeg 3 virtually eliminates the possibility of fine detail or subtle coloring – but it does reduce the file sizes dramatically. The original TIFF of the three flowers is over 0.5 MB (500 Kb), whereas the jpeg 60 version, which is very, very close in appearance is just 32 Kb and the jpeg 3 version is a mere 8 Kb. The Web would not be possible in its present form without compression like this.
What should you do?
JPEG is the principal file format used in digital cameras. Therefore, knowing in broad terms what JPEG is and how it works is like knowing which film to use – it won't guarantee great photos, but it will help you avoid having good photos spoiled because you made the wrong choice.
JPEG has distinct strengths and limitations that you can use to your advantage. They are outlined on About JPEG, with a definite focus on practical use of the format and ideas you can use to make JPEG work for you.
How do you fix it?
Fixing a JPEG that's been compressed more than you like is well nigh impossible. You can make some of the artifacts – the blocks of color and the fringing – less obvious by applying some selective blur followed by sharpening, but you simply cannot recover the lost detail.
Go back to the earliest version of the image file. Perhaps it's on your camera or saved on your computer in a pre-compressed version. If you got the photo from the web, perhaps you can find a larger, less aggressively compressed version somewhere else.
To avoid the problem in future, always set your camera to take "high-quality" JPEGs and save copies of the original files on your computer or on CD. You don't always have to take photos at the largest available pixel dimensions, but if you take "high-quality" JPEGs, you'll have better-looking photos that you can scale up, print and generally do more with. If you need to compress them for the Web or e-mail, you can do that later. For more on choosing compression levels for different purposes, see About JPEG.
