Compression Analyzer

About Compression Analyzer

Geneza Compression Analyzer was made during 1st GENETHON (3rd of December 2013), a coding event dedicated to small, but useful utilities related to digitised images. GENETHON mission is to create tools that will make our everyday operations easier. GENETHON is internal coding event organized by Geneza.

Geneza Compression Analyzer is a completely free tool available to all the professionals worldwide that are missing this kind of tool and of course to general public. It is designed to quickly display effect of JPEG compression on source image.

Many times we are faced with questions about JPEG compression, effect of such compression on original images, file sizes, suitability for archiving as "digital original" and similar. We often also hear that JPEG at high compression ration has no effect on quality of images, which might be true for quick fooling of the eye, but is far from real situation.

The purpose of this tool is not to show if JPEG compression is good or bad, it is meant to display the actual effect on image, so people can decide themselves what level of compression is acceptable to them. We have created this tool using open source technologies (imagemagick mostly) and we allow images up to 20MB of size to be uploaded and analyzed. Your images will be automatically deleted from server by cronjob every few hours. Analysis that you can do with this tool also be done manually in Photoshop or other image manipulation tools, but it will take you considerable amount of time.

JPEG compression introduces three degradations to original image:

  • General loss of sharpness and oscillations around high-contrast edges. These manifest due to approximating intensity transitions with smooth functions (cosines). You see them as small "dots" or "halos" around the edges. They are particularly easy to see in the images of text of hand-drawings.
  • Blocking structure: image is processed separately for every 8x8 block (or bigger in case of chroma downsampling), block edges become visible at high compression ratios.
  • Loss of color detail: it depends on saving parameters, the program may aggressively "downsample" (reduce resolution of) chromaticity channels; it is rarely an issue for the natural photography.

Compression Analyzer sample

How Compression Analyzer works:

  • Your image is uploaded to server, where we create on-the-fly crop of this image, fitting the display area in your browser with selected region from small navigator available on upper right side of interface.
  • This new crop of original file is used to create new JPEG version with compression/quality level that is selected in interface.
  • A pixel-by-pixel difference map is created between new JPEG and original file with grayscale map where lighter color is showing bigger change of color between new and original pixel and darker color is showing smaller change between pixels.
  • A map of differences with lighter version of original shown in background is created. On this display, all pixels that are different from original are colored equally in red. At this display, a special slider is available where user can select a threshold sensitivity to color change of pixels. Slider allows a range between 0-20% of color change to be ignored in display. Please note, that Sensitivity reduction is only preview filter effecting the preview display area, and not the actual number of pixels effected by compression.