Working with Compressed Images

File compression allows you to limit an image’s size by encoding the file’s data more concisely and efficiently. Snowbound imaging SDKs, image viewers, and batch conversion applications enable you to read and write a wide variety of compressed images. Our products support over 100 file formats including the sampling listed below.

TIFF is a popular file format for storing bit-mapped images. Images created in the TIFF file format can be any resolution, and can be black and white, grayscale, or color. The TIFF format is a wrapper around images. It is not a compression format. There are various compression types within the TIFF family. Snowbound supports all of them including CMYK, Compressed, Group 3, Group 4, Huffman, JBIG, JPEG, LZW, Packbits, and Uncompressed.

The JPEG file format is a compression algorithm for 24 bit color and 8 bit grayscale images that greatly reduces image size. JPEG is one of the few formats for which compression can be specified. The JPEG file format compresses small pixel blocks of data that make up an image. As compression is increased, underlying image data for hue and saturation is gradually discarded with very little loss in apparent image quality until compression ratios are quite high. Due to this type of compression, JPEG images are lossy. You cannot recreate an image back to its original state.

Group 3 (G3) and Group 4 (G4) image formats are line-oriented, black and white document formats. Group 3 is more commonly used for faxes. Group 4 is a more popular compression algorithm used for documents. Both can stand alone but typically they are found within a TIFF file format header or within a proprietary document header created by one of a variety of document management companies.

JBIG2 is a highly-compressed black and white image format that uses symbol recognition and substitution for very dramatic compression results. Compression rates of up to 100:1 compared to uncompressed black and white TIFFs are possible. Using the same file, JBIG2 is able to compress data up to 70% smaller than TIFF Group 4. Without sacrificing apparent image quality, it is possible to reduce files to a much smaller size to make it easier to store, download, and transmit. These smaller files can be viewed by virtually anyone across the enterprise. All files saved as a PDF with embedded JBIG2 can be read by Adobe Acrobat 5.0 or higher

Unlike other solutions that use a JBIG2 header but use JBIG compression, Snowbound’s implementation takes full advantage of the standard symbol recognition and substitution technology. For example, a 1 MB uncompressed black and white image can be compressed to 85 KB in Group 4 and 25 KB in Snowbound JBIG2 implementation.

You would call JBIG2 compression as you would save to any other file format. Use the following function to save the file format as JBIG2:

IMG_save_bitmap(“file.jb2”,0,JBIG2);

Additional Resources

  • Image Compression - Snowbound offers a wide range of solutions for the compression and decompression of images and documents
  • Image Conversion - Reliable, high-speed image conversion is one of the fundamental capabilities of every Snowbound Software product.

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