PngSuite - the official set of PNG test images

PngSuite

created by Willem van Schaik

The "official" test-suite for PNG

This is a collection of graphics images created to test PNG applications like viewers, converters and editors. As far as that is possible, all formats supported by the PNG standard are represented.

Web pages

For each test-set there is an html-page containing the PNG images. And for reference purposes another page is provided with the same pictures in a GIF-format.

basic formats	interlacing	odd sizes	background colors	transparency	gamma values
image filtering	additional palettes	ancillary chunks	chunk order	zlib compression	corrupted files

Downloading

For off-line testing you better download the whole suite as a Unix tar-ball or in a Windows zip-file.

Here are the README and LICENSE files.

PNG capabilities

Supported color-types are:

grayscale
grayscale + alpha-channel
color palettes
rgb
rgb + alpha-channel

Allowed bit-depths are depending on the color-type, but are in the range of 1-bit (grayscale, which is b&w) upto 16-bits.

Special features are:

interlacing (Adam-7)
gamma-support
transparency (a poor-man's alpha solution)

File naming

Where possible, the test-files are 32x32 bits icons. This results in a still reasonable size of the suite even with a large number of tests. The name of each test-file reflects the type in the following way:

    filename:                               g04i2c08.png
                                            || ||||
    test feature (in this case gamma) ------+| ||||
    parameter of test (here gamma-value) ----+ ||||
    interlaced or non-interlaced --------------+|||
    color-type (numerical) ---------------------+||
    color-type (descriptive) --------------------+|
    bit-depth ------------------------------------+

color-type:

0g - grayscale
2c - rgb color
3p - paletted
4a - grayscale + alpha channel
6a - rgb color + alpha channel

bit-depth:

01 - with color-type 0, 3
02 - with color-type 0, 3
04 - with color-type 0, 3
08 - with color-type 0, 2, 3, 4, 6
16 - with color-type 0, 2, 4, 6

interlacing:

n - non-interlaced
i - interlaced

Basic formats

These are basic test images in all of the standard PNG b/w, color and paletted formats.

[ PngSuite - basic / PNG-files | PngSuite - basic / GIF-files ]

Interlacing

These are the same basic test images but now using Adam-7 interlacing.

[ PngSuite - interlaced / PNG-files | PngSuite - interlaced / GIF-files ]

Odd sizes

These tests are there to check if your software handles pictures well, with less obvious picture sizes. This is particularly important with Adam-7 type interlacing. In the same way these tests check if pictures size 1 x 1 and similar are ok.

[ PngSuite - sizes / PNG-files | PngSuite - sizes / GIF-files ]

Background colors

When the PNG file contains a background chunk, this should be used for pictures with alpha-channel or pictures with a transparency chunk. For pictures without this background-chunk, but with alpha, this test-set assumes a black background.

For the images in this test, the left-side should be 100% the background color, where moving to the right the color should gradually become the image pattern.

bga - alpha + no background
bgw - alpha + white background
bgg - alpha + gray background
bgb - alpha + black background
bgy - alpha + yellow background

[ PngSuite - background / PNG-files | PngSuite - background / GIF-files ]

Transparency

Transparency should be used together with a background chunk. To test the combination of the two the latter 4 tests are there. How to handle pictures with transparency, but without a background, opinions can differ. Here we use black, but especially in the case of paletted images, the normal color would maybe even be better.

tbw - transparent + white background
tbg - transparent + gray background
tbb - transparent + black background
tby - transparent + yellow background
tp0 - not transparent for reference
tp1 - transparent, but no background chunk
tm3 - multiple levels of transparency, 3 entries

[ PngSuite - transparency / PNG-files | PngSuite - transparency / GIF-files ]

Gamma values

To test if your viewer handles gamma-correction, (3x) 6 test-files are available. They contain corrected color-ramps and a corresponding gamma-chunk with the file-gamma value. These are created in such a way that when the viewer does the gamma correction right, all 6 should be displayed identical.

If they are different, probably the gamma correction is omitted. In that case, have a look at the two right columns in the 6 pictures. The image where those two look the same (when looked from far) reflects the gamma of your system. However, because of the limited size of the image, you should do more elaborate tests to determine your display gamma.

For comparisons, three pages with GIF images are available. Depending on the display gamma of your system, select the NeXT-, the Mac- or the PC-version.

g03 - file-gamma = 0.35, for display with gamma = 2.8
g04 - file-gamma = 0.45, for display with gamma = 2.2 (PC)
g05 - file-gamma = 0.55, for display with gamma = 1.8 (Mac)
g07 - file-gamma = 0.70, for display with gamma = 1.4
g10 - file-gamma = 1.00, for display with gamma = 1.0 (NeXT)
g25 - file-gamma = 2.50, for display with gamma = 0.4

[ PngSuite - gamma / PNG-files | PngSuite - gamma / GIF-files (PC) |
| PngSuite - gamma / GIF-files (Mac) | PngSuite - gamma / GIF-files (NeXT) ]

Image filtering

PNG uses file-filtering, for optimal compression. Normally the type is of filtering is adjusted to the contents of the picture, but here each file has the same picture, with a different filtering.

f0 - no filtering
f1 - sub filtering
f2 - up filtering
f3 - average filtering
f4 - paeth filtering

[ PngSuite - filters / PNG-files | PngSuite - filters / GIF-files ]

Additional palettes

Besides the normal use of paletted images, palette chunks can in combination with true-color (and other) images also be used to select color lookup-tables when the video system is of limited capabilities. The suggested palette chunk is specially created for this purpose.

pp - normal palette chunk
ps - suggested palette chunk

[ PngSuite - filters / PNG-files | PngSuite - filters / GIF-files ]

Ancillary chunks

To test the correct decoding of ancillary chunks, these test-files contain one or more examples of these chunks. Depending on the type of chunk, a number of typical values are selected to test. Unluckily, the test-set can not contain all combinations, because that would be an endless set.

The significant bits are used in files with the next higher bit-depth. They indicate how many bits are valid.

cs3 - 3 significant bits
cs5 - 5 significant bits
cs8 - 8 significant bits (reference)
cs3 - 13 significant bits

For the physical pixel dimensions, the result of each decoding should be a square picture. The first (cdf) image is an example of flat (horizontal) pixels, where the pHYS chunk (x is 1 per unit, y = 4 per unit) must take care of the correction. The second is just the other way round. The last example uses the unit specifier, for 1000 pixels per meter. This should result in a picture of 3.2 cm square.