Image Compression Experiments

on a 3D Model Examiner GUI

JPEG, PNG, GIF files
- - -

This is an image used in the
PNG, JPEG, GIF experiments
below --- experiments in

FE Home page > FE Screenshots page >

JPEG-vs-PNG-vs-GIF page >

Image Compression-versus-Quality Experiments
--- on-a-3D-Model-Examiner-GUI

! Note !
Text, images, file-size-data, or links may be added
or improved --- if/when I revisit this page.

Go to File Size Results, below.

Go to some Conclusions, below.

Go to Start of Test Images, below.


This is a page of experiments in image compression-versus-quality.

Images are shown, and text under each image explains how the image was processed.

Before the images, a summary of file sizes is listed, at the bottom of this introduction --- along with some discussion of how one may be able to get relatively small GIF or JPEG or PNG image files while preserving (for the most part) the quality of the original, captured image.

The summary of file sizes is followed by the images, along with some information about each image, underneath each image.

    If you want to examine the images --- for example, by magnifying them --- you can 'right-click' on each image to do a 'Save As ...' of the image file to your local computer.

    Then you can use image-viewing software on your computer to examine any of these images in great detail.

This page is a link on the 'parent' web page JPEG vs. PNG vs. GIF - quality vs. file size.

The 'Introduction' on that page describes some of the considerations in compressing GIF, JPEG, and PNG files while preserving the quality of the original image (in terms of what the eye can see, without magnifying the image).

See 'The bottom line' section of that page.

It contains a summary of GIF-JPEG-PNG compression-versus-quality guidelines that were deduced from the image compression experiments in these web pages.

The making of the images on this page :

The images on this page were made from an 'original' image in a PNG file.

That 'original' image-file was created by doing an 'entire-screen' capture (to a PNG file) when the GUI was displayed on a computer screen.

The capture was done with the 'gnome-screenshot' utility.

I then used the 'mtpaint' image-editor program to read the PNG file and crop the GUI image from the image of the entire screen.

I saved the cropped image to a PNG file, from the 'mtpaint' program --- which creates rather large PNG files that can be compressed using a utility command like pngcrush.

So the 'original' PNG file was made using the 'gnome-screenshot' and 'mtpaint' programs.

Other, compressed image files (PNG, GIF, and JPEG) were made from this 'original' PNG file by using either

  • the ImageMagick 'convert' command


  • the 'pngcrush' command.

In a little more detail, the steps in making these images were as follows.

  • An image of the entire screen was captured as a PNG file using the 'gnome-screenshot' utility --- on Ubuntu 9.10 Linux, where 9.10 means '2009 October'.

  • The 'mtpaint' image editor program was used to crop the GUI image out of the 'entire-screen' image, and the cropped image was saved as a PNG file.

    That file is the first of the images below.

      (The 'mtpaint' image editor tends to make rather large PNG files --- larger than the PNG file that was read in --- even after some cropping.)

  • Various PNG and JPEG and GIF files are shown below --- in file-size order, largest first.

    Most of the compressed images were made with the ImageMagick 'convert' command.

    One image was made with 'pngcrush'.

  • The JPEG files shown below were made, from the 'original' PNG file at the top of these images, by using the ImageMagick 'convert' command, with the '-quality' and '-sampling factor' and '-filter' options.

    The '-strip' option of the 'convert' command was used to assure that the JPEG file would be stripped of text data such as EXIF text data.

    Experiments on some other PNG image captures have indicated that smaller JPEG files are yielded when the '-sampling-factor 2x2' option is used --- rather than '1x1' or '2x1'.

    Some of those JPEG-making experiments also indicated that the choice of '-filter' may not have a great influence on file-size --- at least not as much influence as '-quality' and '-colors' options.

    So '-filter Mitchell' was used to make these JPEG files.

  • A couple of compressed PNG files were made from the 'original' PNG file at the top of these images, using either

    • the 'convert' command with the '-quality' option.


    • the 'pngcrush' command with the '-brute' option

  • GIF files were made from the 'original' PNG file at the top of these images, by using the 'convert' command with the '-colors' option --- and with '+dither' to turn OFF dithering.

    A range of '-colors' values were used --- from 256 to 4.

  • File-size results are summarized just below.

    See the images further below to examine the image quality.

Below is a list of the sizes (in bytes) and names of the image files shown below --- sorted by size, largest files first.

The filenames indicate the kind of conversion and/or compression that was done.

File size results from various compression tests are listed below --- in file size order --- largest to smallest.

The descriptive file names are quite long and have been 'folded' onto a second line.

The 'original' PNG file:
('mtpaint' makes huge PNG files)

   2,201,589   3DmodelExaminerGUI_PLY_turbineBlades_6618faces_redShaded_

to-JPEG quality-92:
(via ImageMagick 'convert')

     140,943   3DmodelExaminerGUI_PLY_turbineBlades_6618faces_redShaded_

to-PNG via ImageMagick 'convert' PNG-compression:

     115,001   3DmodelExaminerGUI_PLY_turbineBlades_6618faces_redShaded_

to-PNG via 'pngcrush':
(maximal LOSSLESS PNG compression)

     101,255   3DmodelExaminerGUI_PLY_turbineBlades_6618faces_redShaded_

to-JPEG quality-70:

      80,263   3DmodelExaminerGUI_PLY_turbineBlades_6618faces_redShaded_

to-GIF up-to-256-colors:

      65,334   3DmodelExaminerGUI_PLY_turbineBlades_6618faces_redShaded_

to-JPEG quality-50:

      61,907   3DmodelExaminerGUI_PLY_turbineBlades_6618faces_redShaded_

to-GIF up-to-64-colors:

      49,823   3DmodelExaminerGUI_PLY_turbineBlades_6618faces_redShaded_

to-GIF up-to-32-colors:

      41,956   3DmodelExaminerGUI_PLY_turbineBlades_6618faces_redShaded_

to-GIF up-to-16-colors:

      34,780   3DmodelExaminerGUI_PLY_turbineBlades_6618faces_redShaded_

to-GIF up-to-4-colors:

      19,959   3DmodelExaminerGUI_PLY_turbineBlades_6618faces_redShaded_

See quality of these images in the images section below.

The file-size-versus-image-quality is noted below the images.

PNG vs. GIF vs. JPEG :

Note that we achieved the maximum loss-less compression of the PNG file to another PNG file with the '_pngcrushBRUTE.png' file --- created with the 'pngcrush' command with the '-brute' option.

We also created a PNG file about 20 times smaller than the 'original' by using the ImageMagick 'convert' command with a '-quality' compression parameter of '00'.

    For the PNG '-quality' parameter of 'convert':

    • 00 is recommended for images with mostly AREAS OF SOLID COLORS.

    • 05 is recommended for images like NATURAL LANDSCAPES.

    • 00 and 90 seem to give small file sizes with good quality for these images.

    The first digit (tens) is the zlib compression level, 1-9.

    However if a setting of '0' is used you will get Huffman compression rather than 'zlib' compression, which is often better!

    The second digit is the PNG data encoding filtering type (before the data is compressed):

    • 0 is none
    • 1 is 'sub'
    • 2 is 'up'
    • 3 is 'average'
    • 4 is 'Paeth'
    • 5 is 'adaptive'.

    The filters did not seem to affect the file sizes significantly, so we used filter-type zero (none).

We can get still smaller files, than these PNG files, by allowing some 'lossiness' --- by going to GIF files (with a max of 256 colors) or by using the 'lossy' compression inherent in creating JPEG files.

On GIF :

Since this GUI image contains a canvas area on which a shaded-image of a turbine assembly is displayed --- and that shaded image is composed of hundreds of shades of a reddish color --- we can expect that we are going to lose some image quality if we convert the 'original' PNG file to a GIF file ---- even if we choose to specify the maximum of 256 colors.

In fact, it turned out that for this GUI image, when we go down to 32 colors, the GIF file differs quite markedly in appearance from the 'original' PNG file from which it came.

Many 'facets' on the turbine have disappeared.

And when we go to 16 and 4 colors, most of the facets disappear.

    (We could try converting the 'original' PNG file to PNG files with a restricted number of colors --- such as 256 or 16 --- but if we are going to do that, I would rather use GIF --- since it has been supported by web browsers for about 10 more years than PNG --- and there may be some cases of software not reading certain types of PNG files.)


Note that when text fonts (in a quite contrasting color to their background) are in an image, the 'lossy' compression of JPEG typically introduces 'mosquito noise' around the text characters --- especially when we use a 'convert' '-quality' value lower than the range of 100 to 92.

In this GUI image, there are many 'fine', small text characters --- so we DO have to be concerned about introducing 'mosquito noise' when converting the 'original' PNG file to a JPEG file of '-quality' less than 92.

These JPEG files DO show appreciable 'mosquito noise' --- which, on close examination, is seen in the '-quality 70' JPEG file --- and even more so in the '-quality 50' JPEG file.

On choosing a file-type :

For this particular image, IF file size was my main concern (for example, if I were posting the image on a web page along with a lot of other images), I would be tempted to use a GIF file with '-colors 256' (or perhaps 128 or 64) --- rather than use the about-twice-as-large loss-less, maximally-crushed PNG file.

I would NOT be tempted to use a JPEG file, because the high-quality '-quality 92' JPEG is larger than either of the two compressed PNG files --- and the '-quality 70' and '-quality 50' JPEG files are showing 'mosquito noise' around the text items on the GUI.

If file size was not a main concern (for example, if this were the only large image on a web page), I might choose to use one of the compressed PNG files --- because no colors have been lost from the image by the PNG-compression.

To me, it COULD be almost a coin-flip whether to use one of the compressed-PNG files or the GIF-colors-256 image file of this GUI.

If it proved to be the case that a GIF file would load into a web page faster (or with less CPU processing) than the PNG file, then I would probably choose to use the GIF file.

Below are the images. Judge for yourself.

(Click on these images to see them
in a separate window or tab.)

The 'original' cropped PNG file from
'gnome-screenshot' and 'mtpaint'.
File size: 2,201,589 bytes
(The 'mtpaint' image-editor saves to
a rather large PNG file.)

JPEG from
'convert -quality 92 -sampling-factor 2x2 -filter Mitchell'
File size: 140,943 bytes
There is NO apparent 'mosquito noise' around
the text items --- in a quality-92 JPEG file
created from the original PNG file.

PNG from 'convert -quality 00'
File size: 115,001 bytes
Nice quality and almost 20 times smaller than the
'original' PNG file, with this compressed PNG.
About 20% smaller than the 'quality 92' JPEG file.

PNG from the 'pngcrush' command
with the '-brute' option.
File size: 101,255 bytes
About 20 times smaller than the 'original' PNG file
from 'mtpaint'. This is the smallest PNG we can get
without sacrificing some colors.

JPEG from
'convert -quality 70 -sampling-factor 2x2 -filter Mitchell'
File size: 80,263 bytes
If you look closely, at this JPEG-quality-70 level,
'mosquito noise' is apparent around the text items.

However, if you wanted a file about 20% smaller
than the smallest PNG file, above, you might
tolerate this level of 'mosquito noise' and
use a JPEG file lossy-compressed to this extent.

GIF from
'convert -colors 256 +dither' (no dithering).
File size: 65,334 bytes
There is no 'mosquito noise' generated in
non-dithered GIF files, so none in this one.
And if there were many colors lost in
generating this 256-color GIF file, it is not
readily apparent in the turbine and its facets.

This image looks quite usable, and it is about
40% smaller than the smallest PNG file, above.

JPEG from
'convert -quality 50 -sampling-factor 2x2 -filter Mitchell'
File size: 61,907 bytes
Even if you could not detect the 'mosquito noise'
in the quality-70 JPEG image a couple of images above,
you should be able to see considerable 'mosquito noise'
around text in this quality-50 JPEG image.

GIF from
'convert -colors 64 +dither' (no dithering).
File size: 49,823 bytes
Some of the facets have disappeared
in this colors-64 GIF image.

GIF from
'convert -colors 32 +dither' (no dithering).
File size: 41,956 bytes
LOTS of the facets have disappeared
in this colors-32 GIF image.

GIF from
'convert -colors 16 +dither' (no dithering).
File size: 34,780 bytes
MOST of the facets have disappeared
in this colors-16 GIF image.

GIF from
'convert -colors 4 +dither' (no dithering).
File size: 19,959 bytes
Even the text areas of the GUI have significantly
degraded in this 4-color GIF image.


Some other PNG-JPEG-GIF compression-versus-quality experiments (using different image types) are available from the 'parent' page of this page --- the JPEG vs. PNG vs. GIF - image-quality vs. file-size page.

'External' WEB LINKS to
other JPEG/PNG/GIF info :

For more information on image file quality and compression issues, for JPEG and PNG and GIF files, you can try the following WEB SEARCHES on the indicated keywords.

You may wish to change or add keywords to these queries in order to hone in on answers to your particular questions.

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Image Compression Experiments -
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Page history:

Page was created 2015 Feb 03.

Page was changed 2018 Aug 18.
(Added css and javascript to try to handle text-size for smartphones, esp. in portrait orientation.)

Page was changed 2019 Jul 12.
(Specified image widths in percents to size the images according to width of the browser window. Also added some web links.)