JPEG Compression and Optimization
JPEG is a widely accepted standard for compressing photographic images. VIMAS JPEG engine designed to keep maximum image quality, while performing this lossy compression algorithm. It is used in VIMAS image optimization utility Web Image Guru and in software development kit VIMAS Imaging SDK. Below briefly described JPEG optimization parameters available in these VIMAS products.
1. JPEG Compression.
Compression is the main JPEG optimization parameter. It defines the compression level of the image. As you may see from Fig.1 and Fig.2, the larger its value - the smaller file size and worse image quality. Web Image Guru has effective preview engine to simplify the search of the optimum trade-offs between image quality and file size. You may estimate the quality of the VIMAS JPEG compressor in the pictures below or examine more examples here.
Fig.1 Web Image Guru JPEG
Compression 25, File size 16.3 K
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Fig.2 Web Image Guru JPEG
Compression 105, File size 6.8 K
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2. JPEG Color Tuning.
Color Tuning is used to change compression level of the color component (Chrominance compression ratio). Negative values reduce, and positive increase compression ratio of chrominance component. Fig.3 displays image compressed by Jasc Paint Shop Pro 8 that doesn't have such control. It has more smudged left part (and larger file size!) than image optimized by Web Image Guru with using Color Tuning feature.
Fig.3 Jasc Paint Shop Pro 8 JPEG
File size 6.96K
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Fig.4 Web Image Guru JPEG
Compression 75, File size 6.80K
Color Tuning -30
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3. JPEG Subsampling.
Subsampling lets you specify stronger image compression by discarding some unimportant color information. It produces artifacts visible on the sharp color edges, as on left part of Fig.5. JPEG images without Subsampling have more artifacts in regions with sharp details, as in the top and bottom-right parts of Fig.6.
Fig.5 Web Image Guru JPEG
File size 6.80 K, Subsampling On
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Fig.6 Web Image Guru JPEG
File size 6.80 K, Subsampling Off
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4. Sharpness.
Sharpness lets you, by using value less than 100, perform some additional image smoothing during JPEG compression. Setting this parameter to value 0 usually will result in smallest file size, but not as sharp as possible image. This feature is very useful for heavily compressed images. Setting Sharpness to 0 allows greatly reduce artifacts in text and face areas on Fig.8.
Fig.7 Corel Photo Paint 12 JPEG
File size 6.80 K, Subsampling Off
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Fig.8 Web Image Guru JPEG
File size 6.80 K, Subsampling Off
Sharpness 0
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5. Weighted JPEG optimization.
Weighted optimization in JPEG compression lets to compress different areas of a JPEG image at different levels. Images on Fig.9 and 10 have equal file sizes, but the last one has better quality text areas due to the weighting (stronger compression) of the central girl photo.
Fig.9 Web Image Guru JPEG
File size 6.80 K, No weighting
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Fig.10 Web Image Guru JPEG
File size 6.80 K, Weighting On
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VIMAS image processing technologies:
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