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© December 2005
revised 28 September 2009

Supplementary graphic file formats test page: JPEG-2000

This page supplements an earlier set of JPEG-2000 compression tests, completed in November 2005, which also made a case study of antique maps.

For the first set of trials, the two TIFF files I compressed were lower-resolution images (one grayscale, one true color), of the sort deemed more appropriate for Web publication when file size and download time are the primary concerns. In general, I follow a guiding principle that the quality of compressed images I post to the Web should be good enough for serious research and scholarship, but of as small a file size as possible. The sort of high resolution required for peer-reviewed publication or intense scholarly scrutiny is not, in most cases, a necessity. Hence, I try to keep all enlargements within a range of 1000–3000 pixels wide, with a 1000-pixel width, the norm.

There are, however, select cases where a higher resolution than the norm is desirable, and the image tested here — 8040x5702 pixels — falls in that category. With so many pixels to describe, the starting file size is a hefty 131.18MB.

This test image of what is now known as “the Velasco map” was prepared upon request for a colleague who has need of the higher resolution. Indeed, two lower-resolution versions of the image have already been posted to she-philosopher.com —

  • the 740x526 pixel image that appears at the top of the first of five Gallery Exhibits on color and/or modern reproductions of the Velasco Map, and

  • the 2650x1884 pixel image accessible from the “View an enlarged 2650 x 1884 pixel JPG image” link immediately below

— and are, I believe, more than adequate for most purposes. By way of comparison, the latter lower-resolution 2650x1884 pixel image is a 1,039,030 byte (0.99MB) JPG file, which I compressed from a starting TIFF file of 14.30MB using Photoshop’s “Save for Web” JPG codec (my driver of choice for the bulk of images I post to the Web).

Given that the high-resolution 131.18MB TIFF file tested here is about 9 times the size of the TIFF file used to produce the lower-resolution versions of the Velasco Map already posted, I expected the JPEG-2000 compression format to substantially out-perform standard JPEG, GIF and PNG formats.

It did not.

Indeed, the default settings in the LEAD Technologies plug-in for Photoshop produced a compressed file of 5.25MB, slightly larger than the 4.85MB file I was able to produce with Photoshop’s “Save for Web” JPG codec.

As before, optimal compression requires experimentation, and manual tweaking of the JPEG-2000 driver’s standard and advanced settings. Having done this, I was able to come up with a compressed file size of 2.62MB, but even this file size is matched by Photoshop’s “Save for Web” JPG driver, using its LOW setting (2.78MB). Unfortunately, I could not ascertain the quality of this compressed file, as Photoshop was unable to write the file to disk without using more memory than my system has available. I suspect image quality would be comparable, though.

For the current set of tests, I have used knowledge gained from the first go-round to streamline the process a little (a necessity, given the large size of the files, both compressed and uncompressed).

As user feedback has shown the files produced with LEAD Technologies’ JPEG-2000 plug-in for Photoshop to be most reliable, this time around, I limited my tests to this particular codec. I also chose to restrict my JPEG-2000 file types to the standard JP2 (i.e., no J2K tests were made).

Although I created a range of test files using IrfanView’s JPEG driver, I decided to discard these as none of them met the quality of the comparably-sized JPEG files generated with Photoshop. Hence, no references to these IrfanView-generated JPEG files appear below in the table of results or data sets.

While I have included results for PNG and GIF compression schemes in the table that follows, I have not included links to any sample files. The PNG test files I generated were still way too large for posting to the Web (the smallest being a hefty 21.57MB), and all showed some loss of detail. Similarly, the one GIF test file I created was even larger (24.61MB), and had even more noticeable loss of detail (probably due to the driver’s 256-color limit).

In general, the JPEG-2000 files take longer to load than comparably-sized JPEG files (e.g., 11 seconds for a 5.25MB JP2 file versus 3.5 seconds for a 5.70MB JPG file). While an 11-second load time is long enough to require a user caveat, my 2.62MB JPEG-2000 file of choice loaded in a speedy 0.7 seconds, alleviating this concern.

In sum, I continue to question the efficacy of using the JPEG-2000 compression scheme on antique maps of the kind tested here.

It would appear that the much-touted JPEG-2000 advantage pertains mostly to more complex image structures (e.g., continuous tone photographs) than is typical of the 17th-century maps and engravings with which I tend to work.





quick links

MapHist discussion list

InfoDesign Café discussion list

(My thanks to subscribers on both lists for their feedback on earlier tests & for sustained debate of the issues.)


first set of JPEG-2000 tests
(conducted in November 2005)

compressed files = lower-resolution images of the Smith & Block maps


lower-resolution JPG images of the Velasco Map already posted to she-philosopher.com

see the first of five Gallery Exhibits on color and/or modern reproductions of the Velasco Map



Summary List of Test Results: Comparison of
JPEG-2000, JPEG, GIF, and PNG Compression Formats
       
COMPRESSION FORMAT
HI-RESOLUTION
24-bit true color TIFF image
(131.18MB)
   JPEG-2000: JP2 file format
Lead Technologies Photoshop plug-in
2.62MB
compression ratio = 50
load time: 687 milliseconds
   browser-compliant JPEG
Photoshop “Save as” JPG codec
5.70MB
quality = 6
load time: 3500 milliseconds
Photoshop “Save for Web” JPG codec
4.85MB
quality = medium (30)
load time: 3438 milliseconds
2.78MB
quality = low (10)
load time: n/a
   browser-compliant GIF
Photoshop “Save for Web” GIF codec
24.61MB
colors = 256 (max.)
load time: n/a
   browser-compliant PNG
Photoshop “Save as” PNG codec
75.18MB
n/a
load time: n/a
Photoshop “Save for Web” PNG-8 codec
21.57MB
colors = 256 (max.)
load time: n/a
Photoshop “Save for Web” PNG-24 codec
75.18MB
colors = 256 (max.)
load time: n/a
NOTE: Load times given here are from IrfanView, and document the amount of time it takes a viewer to decode a compressed graphics file and display its complete contents onscreen. Because load times will vary according to computer speed and configuration, they will not be the same for every desktop. The meaning of the load times given above comes from comparing them across compression formats, and is not to be found in the absolute values.

    test case: Large, high-resolution true color
    image

(24-bit color = 16.7 million colors)     


Map of North America, aka “the Velasco Map” (1610/11)

The "Velasco Map" (1610/11)

Size of original image (TIF file):

  • 8040 x 5702 pixels
  • 137,553,272 bytes (131.18MB)



JPEG-2000 compression: JP2 file format

A NOTE ON SETTINGS FOR:

Lead JP2 driver for Photoshop (plug-in)

· image starts degrading above a compression ratio of 50 (although even at a ratio of 80, image is still pretty good)
     
PREFERRED = setting of 50

· quality factor settings track compression ratio settings exactly (so I have not included any examples of this)
     
PREFERRED = setting of 50

· 24-bit setting (bits per pixel option) produces better compression with a true color image (default is 24-bit)
     
PREFERRED = 24 bits per pixel

· higher decompression levels result in smaller files, but unsightly bars appear in the upper margin (above the map’s top border) with a setting of 7 (range is from 1 to 7, with default of 5)
     
PREFERRED = setting of 4

· larger tile sizes produce slightly better compression (default is 640x480)
     
PREFERRED = 8040x5702 (same as image size)

· progressing order option does not affect compression file size, but only how an image loads and decompresses (default is quality-axis order, where image starts out blurry and becomes clearer and more detailed as additional data is decoded)
     
PREFERRED = quality-axis order (default)

RESULTING TEST FILES:

  • compressed file = 1,964,857 bytes (1.87MB)
    Velasco_LeadCR70t8040x5702.jp2
    file compressed in Photoshop using LEAD Technologies JP2 plug-in
    driver settings: lossy data compression (compression ratio of 70, 24 bits per pixel, decompression level of 4, tile size of 8040x5702)
    compressed image loaded in: 11281 milliseconds

  • compressed file = 2,750,766 bytes (2.62MB)
    Velasco_LeadCR50t8040x5702.jp2
    file compressed in Photoshop using LEAD Technologies JP2 plug-in
    driver settings: lossy data compression (compression ratio of 50, 24 bits per pixel, decompression level of 4, tile size of 8040x5702)
    compressed image loaded in: 12000 milliseconds

  • compressed file = 5,501,416 bytes (5.25MB)
    Velasco_HIRES(8040x5702).jp2
    file compressed in Photoshop using LEAD Technologies JP2 plug-in
    driver settings: DEFAULTS for lossy data compression (compression ratio of 25, 24 bits per pixel, decompression level of 5, tile size of 640x480)
    compressed image loaded in: 10953 milliseconds

  • compressed file = 5,501,417 bytes (5.25MB)
    Velasco_LeadCR25t8040x5702.jp2
    file compressed in Photoshop using LEAD Technologies JP2 plug-in
    driver settings: lossy data compression (compression ratio of 25, 24 bits per pixel, decompression level of 4, tile size of 8040x5702)
    compressed image loaded in: 14172 milliseconds


tabular summary of test results
top of page



JPEG compression: JPG file format

A NOTE ON SETTINGS FOR:

Photoshop “Save for Web” JPG driver

· best compression achieved with medium setting (quality of 30)
NOTE: the compression process would not complete with a setting of low (quality of 10); Photoshop reported being unable to write the file to disk because of insufficient memory
     
PREFERRED = medium

Photoshop “Save as” JPG driver

· image begins to degrade below a setting of medium; range is from a setting of low (quality of 3), to medium (quality of 6), to high (quality of 8), to maximum (quality of 10)
     
PREFERRED = medium (quality of 6)

RESULTING TEST FILES:

  • compressed file = 5,090,443 bytes (4.85MB)
    Velasco_PhotoshopSfWMED.jpg
    file compressed in Photoshop using its “Save for Web” JPEG file format driver
    driver settings: defaults for medium quality
    compressed image loaded in: 3438 milliseconds

  • compressed file = 5,978,149 bytes (5.70MB)
    Velasco_Photoshop.jpg
    file compressed in Photoshop using its “Save as” JPEG file format driver
    driver settings: defaults for medium quality
    compressed image loaded in: 3500 milliseconds


tabular summary of test results





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