A utility for processing PNG, JPEG, BMP, and WebP images. Features include resize/resample, dither, grayscale, apply background color, subpixel rendering.
ImageWorsener is a raster image scaling and processing utility.
Version 1.3.5
Copyright © 2011-2022 Jason Summers [email protected]
Web site: https://entropymine.com/imageworsener/
All nontrivial automated image processing causes a loss of information.
While ImageWorsener will degrade your images, its goal is to degrade them as
little as possible.
===========================================================================
This program is distributed under an MIT-style license. Refer to the
included COYPING.txt file for more information.
Versions up to 1.1.0 used the GPLv3+ license.
If source code is not included in this package, it may be downloaded from
the web site at https://entropymine.com/imageworsener/.
===========================================================================
If this package contains executable binaries, we need to state the following:
This software is based in part on the work of the Independent JPEG Group.
This software may include code from libwebp (part of the WebM project), which
has the following license:
| Copyright © 2010, Google Inc. All rights reserved.
|
| Redistribution and use in source and binary forms, with or without
| modification, are permitted provided that the following conditions are
| met:
|
| * Redistributions of source code must retain the above copyright
| notice, this list of conditions and the following disclaimer.
|
| * Redistributions in binary form must reproduce the above copyright
| notice, this list of conditions and the following disclaimer in
| the documentation and/or other materials provided with the
| distribution.
|
| * Neither the name of Google nor the names of its contributors may
| be used to endorse or promote products derived from this software
| without specific prior written permission.
|
| THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
| “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
| LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
| A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
| HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
| SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
| LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
| DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
| THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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| OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
===========================================================================
For additional information about ImageWorsener, see the file technical.txt.
Primary features:
ImageWorsener is focused on correctness, and not on performance. It is
relatively slow. Among the things it (hopefully) does right:
Other information:
Unfortunately, there is no documentation for the library, aside from the
comments in the imagew.h header file. The original idea was to have a well-
designed, stable, and documented library, but that hasn’t worked out very well.
The API won’t be broken for no reason, but I can’t make promises about
compatibility between versions.
Synopsis
imagew [options]
Options may appear anywhere on the command line, even after the file names.
The order of the options usually does not matter.
that resources other than regular files can be supported. If your filename may
contain a colon, prefix it with “file:”. In the Windows version, you can use
“clip:” to refer to the clipboard.
A scheme of “stdin:” or “stdout:” means the standard input or output stream
(this may not be supported for all formats). As a shortcut, a file name of
“-” may be used instead.
Numbers on the command line may be specified as rational numbers, using a
slash. For example, instead of “-w x0.666666666”, you can use “-w x2/3”.
Options:
-w
-s
-S
The width and height of the output image.
number of pixels.
Using the -s option, or specifying only one of the width or height, will
cause the “bestfit” feature to be enabled.
Using the -S option, or specifying both the height and width, will cause
“bestfit” to be disabled, so the image will have the exact size you request.
If you use a prefix of “x”, for example “-w x1.5”, then the new size will
instead be that number multiplied by the size of the source image.
-bestfit
-nobestfit
Explicitly enable or disable the “bestfit” feature. If enabled, the image’s
shape will not be changed.
-noresize
Ensures that the image will not be resized at all. This is only useful if
the source image may have non-square pixels.
Incompatible with -bestfit and the sizing options.
-imagesize
The other sizing options set the size of the entire output image. Normally,
the region of that image corresponding to the input image will be that same
size. However, you can use -imagesize to make that region be a different
size. For example, you can shrink the image, to effectively
add a border around it.
Note that
If you use -imagesize, you should probably also use -translate and
“-edge t”.
-infmt
Specifies the image file format of the input or output file. If not used,
imagew will try to figure out the format based on the contents of the file,
or the file name.
Valid values for
png: PNG
jpeg, jpg: JPEG
webp: WebP
bmp: Windows BMP
gif: GIF (-infmt only)
tiff, tif: TIFF (-outfmt only)
miff: MIFF (experimental; limited support)
pnm, ppm, pgm, pbm: Netpbm formats (only the binary formats are supported,
not the rare “plain”/ASCII variants)
Within the overall depth, you can reduce the number of colors that will
actually be used, by using the “-cc” options.
Note that this doesn’t necessarily determine the depth used in the output
file. If the image can be encoded at a smaller depth with no loss of
information, IW may choose to do that (see also -noopt).
The -depthcc option sets the depth based on the number of color levels,
instead of the number of bits used to represent a color level. For example,
“-depthcc 32” is equivalent to “-depth 5”. This allows for greater
flexibility, if the output format supports it. Currently, it’s only useful
with PPM, PGM, and PAM formats.
-sampletype
Request that the output samples be written as unsigned integers (type=“u”),
or floating-point (type=“f”). This option currently has no effect.
-filter
The resizing algorithm to use. (It would be more accurate if this option
were named “-resizealgorithm”, but that’s too hard to type.) Default is
“auto”.
With -filterx and -filtery, you can use different algorithms for the
horizontal and vertical dimensions. (This is possible because IW supports
only “separable” resizing algorithms.) This may occasionally be useful for
something, such as if you need to enlarge an image in one dimension while
reducing it in the other.
IW uses the filter even if the image size isn’t being changed. Many
filters will leave the image unchanged in that case, but some (such as
bspline, mitchell, gaussian) will cause it to be blurred, at least
slightly.
Some filters are not particularly good for general purposes. The main
filters you should consider using are lanczos, mitchell, lanczos2, catrom,
and mix.
Full list:
nearest, point
Nearest-neighbor resizing.
mix
Pixel mixing, a.k.a. area map. Not good for enlarging images, unless you
want a pixelated effect.
box
Box filter.
boxavg
A slightly modified box filter, which is more well-behaved and symmetric,
but less standard. Refer to technical.txt for more information.
triangle, linear
Triangle filter. When upscaling, this is the same as (bi)linear
interpolation. When downscaling, the term "linear interpolation" is
ambiguous -- see the "-blur x" option.
gaussian
Gaussian filter, evaluated out to 4 sigma.
quadratic
Quadratic interpolation. A rough approximation of a Gaussian filter.
cubic<B>,<C>
Generalized cubic interpolation as defined by Mitchell-Netravali.
The usual range of both B and C is from 0 to 1.
keys<n>
This is a subset of the cubic filters. The normal range of n is from
0 to 0.5.
"keys0" = "cubic1,0" = "bspline"
"keys1/3" = "cubic1/3,1/3" = "mitchell"
"keys0.5" = "cubic0,0.5" = "catrom"
hermite
Hermite filter. Identical to "cubic0,0".
bspline
B-Spline filter. Identical to "cubic1,0".
mitchell
Mitchell filter. Identical to "cubic1/3,1/3".
catrom
Catmull-Rom spline. Identical to "cubic0,0.5".
lanczos<n>
Lanczos filter. n is the number of "lobes", and defaults to 3.
blackman<n>
Blackman filter. This is a windowed sinc filter, similar to Lanczos.
n is the number of "lobes", and defaults to 4.
hanning<n>, hann<n>
A Hanning filter. This is a windowed sinc filter, similar to Lanczos.
n is the number of "lobes", and defaults to 4.
sinc<n>
An unwindowed sinc filter. n is the number of "lobes", and defaults to 4.
For experimental use only. This filter will almost always produce poor
results.
auto
The default. IW will select a filter to use. Currently uses "catrom",
unless the size is not being changed and "null" can be used.
null
No resizing. No need to specify this, but it's documented because it may
be selected by the "auto" method.
-blur
-blur x[
Adjust the width of the resampling filter.
This is really a parameter of the resampling filter: if you use -blur,
you should also use -filter. “-blur” does not work with some algorithms,
such as “nearest”.
The default value is 1.0. Larger values blur the image more. A value
smaller than 1 may sharpen the image, at the expense of aliasing. But a
value that’s too small will cause some pixels to be missed completely,
leaving black lines.
If the “x” prefix is used, and the image is being downscaled, the blur
factor will be multiplied by the scale factor. If
defaults to 1.
The purpose of the “x” option is to make it easy to perform simple
interpolation. For example, use “-filter linear -blur x1” to do linear
interpolation. This is not a good way to downscale images, but it is
what many applications do.
-edge
The strategy for dealing with the pixels near the edges of images.
Strategies available:
“s” (for “standard”): This is the default strategy. Instead of inventing
samples that are beyond the edge of the source image, give extra weight
to the smaller-than-usual number of samples that are available. If no
samples are available, the pixel will be colored black or be
transparent. This can happen if you use -translate or -offset.
“r” (for “replicate”): Pixels beyond the edges of the image are assumed to
be the color of the nearest pixel within the image.
“t” (for “transparent”): Pixels beyond the edges of the image are assumed
to be transparent. Note that this can be used with -bkgd.
-intclamp
IW always resizes the image first vertically, then horizontally, then
“clamps” the sample values to the normal visible range (usually thought of
as being from 0 to 255).
With -intclamp, clamping is also done to the “intermediate” image, after
the vertical-resize operation. This is not the correct thing to do,
though the difference usually isn’t noticeable. The purpose of this option
is to let you try to replicate what some other applications do.
Exception: If you are writing to a MIFF file, samples are never clamped,
unless you use -intclamp, in which case both the intermediate and final
samples are clamped.
-reorient
Rotate or mirror the image.
Available operations:
“5” or “rotate90”: Rotate 90 degrees clockwise.
“3” or “rotate180”: Rotate 180 degrees.
“6” or “rotate270”: Rotate 270 degrees clockwise.
“1” or “fliph”: Flip horizontally (across a vertical axis).
“2” or “flipv”: Flip vertically (across a horizontal axis).
“4” or “transpose”: Flip across upper-left-to-lower-right axis.
“7” or “transverse”: Flip across upper-right-to-lower-left axis.
“0”: No change.
Rotating/mirroring causes the source image to be interpreted as if it had a
different orientation. So, all other options (-width, -crop, etc.) are based
on the new orientation, not the original.
-crop
Crop the source image before processing it. Pixels outside the specified
area will be ignored.
The parameters are in pixels. (0,0) is the upper-left pixel.
If
right or bottom edge of the image.
-grayscale
Convert the image to grayscale.
The image will be converted to grayscale early in the processing pipeline,
and only a single grayscale channel (and possibly also an alpha channel)
will be processed from then on. Occasionally that makes a difference, such
as when using the “r” (random) dithering method.
-condgrayscale
Conditionally process the image as grayscale.
If the input image is encoded as a grayscale image, behave as if
“-grayscale” were used. This is not dependent on whether the image actually
contains non-gray colors; it’s about whether it’s encoded in a way that
could support non-gray colors. The exact meaning is dependent on the input
file format.
Be aware that, just because IW encoded an output image as grayscale,
doesn’t mean it processed it as grayscale. If the final image happens to
contain only grayscale colors, IW may choose to optimize it by encoding it
as grayscale. (So, you probably shouldn’t use -condgrayscale on images that
were created by IW, if you want predictable results.)
-gsf
The formula to use when converting a color image to grayscale. Using -gsf
implies -grayscale, unless -condgrayscale was used.
Available options:
s (default) = The standard formula, based on luminance. Equivalent to
“w0.212655,0.715158,0.072187”. This is usually what you should use.
c = The “compatibility” formula. Equivalent to “w0.299,0.587,0.114”.
This should generally only be used with -nogamma.
w
The weights will be normalized so that they add up to 1.
v
maximum, middle, and minimum value. That is, the first weight will be
applied to whichever component of that pixel has the largest value, etc.
“v1,0,0” and “v0.5,0,0.5” have been suggested as grayscale conversion
formulas, though they should be used with caution.
-negate
Negate the image’s colors. The operation is performed in the output
colorspace. If a background color is applied to the image, it happens before
negation, so the background will be negated. If a background color label is
written to the file, it is not affected by -negate.
-bkgd
Apply a background color to the transparent and partially-transparent parts
of the image. This is the only way to remove transparency from an image.
The color uses an HTML-like format with 3, 6, or 12 hex digits. For
example:
-bkgd f00 = bright red
-bkgd ff0000 = the same red color as above
-bkgd ffff00000000 = the same red color as above
-bkgd 999 = medium gray
Colors with transparency may also be specified, by using 4, 8, or 16 hex
digits. The final component is the alpha value (0 means fully transparent).
The alpha value will be ignored if the image format does not support
transparency.
Background colors are always specified in the sRGB color space. They will
be converted to whatever colorspace is used by the image.
If you supply two colors, a checkerboard background will be used.
This does not affect the background color label that may be written to the
output image’s metadata. Use -bkgdlabel for that.
-checkersize
For checkerboard backgrounds, specifies the size of the squares in pixels.
The default is 16.
-checkerorigin
For checkerboard backgrounds, adjust the position of the checkerboard
background.
-usebkgdlabel
If the input file contains a background color label (e.g. a PNG bKGD chunk),
and you used the -bkgd option, IW has to decide which of these background
colors to prefer in the event that a background is applied to the image.
Normally, it prefers the color from the -bkgd option. But if you use the
-usebkgdlabel option, it will prefer the color from the input file.
-bkgdlabel
Specify the background color to write to the output file’s metadata, if
supported by the file format. The color is always given in the sRGB
colorspace. The format of
-nobkgdlabel
Do not copy the input file’s background color label to the output file.
Incompatible with -bkgdlabel.
-cc
-cc
Posterization. “cc” stands for “color count”.
The maximum number of different values (brightness levels, opacity levels)
to use in each channel, including the alpha channel if present.
The available values will be distributed as evenly as possible from among
the possible values (based on -depth) in the output color space. An
optimized palette is not used. If you use “-cc”, consider also using
“-dither”.
The -cc option should usually not be used when writing to a lossy image
format (JPEG, WebP). Lossy formats do not store colors precisely enough,
so the resulting image will have more colors than requested.
If you use -cc expecting to get a PNG image in a particular format, be aware
that background color labels are not affected by -cc, and can prevent some
image format optimizations from occurring. For example, “-grayscale -cc 2”
will not always produce a 1-bpp grayscale image, unless you also use
-nobkgdlabel.
The -ccX options let you have a different setting for different channels.
If you specify overlapping options, the most specific option will have
priority.
-cccolor affects all channels except the alpha channel.
-ccalpha affects only the alpha channel. Use “-ccalpha 2” for binary
transparency.
-ccgray applies only if you force grayscale output, using “-grayscale”.
-dither
-ditherblue -dithergray)
Enable dithering.
Dither types available:
“none”: No dithering.
“f” or “fs”: Floyd-Steinberg.
“o”: 8x8 Ordered dither.
“halftone”: A sample 8x8 halftone dither.
“r”: Random dither. See also the -randseed option.
“r2”: “Random2” dither - Same as Random, except that all color channels
(but not alpha) use the same random pattern. The colors will be more
consistent than with Random, but the image will be grainier.
“sierra” or “sierra3”
“sierra2”
“sierralite”
“jjn”: Jarvis, Judice, and Ninke.
“burkes”
“atkinson”
You can enable dithering on any image, no matter how many colors it uses.
However, if lots of colors are available, the dithering effect will be
invisible to the human eye (unless you use a paint program to turn the
image’s contrast way up). Normally, if you enable dithering, you should
also use one or more of the “-cc” options to limit the number of colors
available.
If you are applying a background to an image with transparency, dithering
is only done after the background has been applied, so -ditheralpha has no
effect. There’s no way to dither the alpha channel and then apply a
background, unless you invoke IW multiple times using an intermediate image
file.
-cs
The colorspace to use for the output image. Ideally, the image should will
look about the same regardless of what colorspace you choose. But it
might not if your viewer doesn’t support color correction, or the image
format doesn’t support colorspace labels, or IW doesn’t know how to write
an appropriate label, or you use the -negate option. This is fairly safe to
use when writing PNG files, but should be used with caution with most other
formats.
gamma” like 0.4545"). “g1.0” is the same as “linear”.
“srgb”: sRGB colorspace. Can optionally be followed by a letter indicating
the “rendering intent” (equivalent to using the -intent option):
p=perceptual, r=relative, s=saturation, a=absolute.
“rec709”: The color response curve defined by ITU-R Recommendation BT.709
(Rec. 709).
By default IW will choose a colorspace that works with the output format;
almost always sRGB.
-intent
Specify the color profile “rendering intent” setting to be written to the
output file. This does not affect image processing.
By default, the rendering intent of the input image will be used. If that’s
not possible, a default setting will be used that may depend on the output
image format.
Rendering intents available:
“p” or “perceptual”
“r” or “relative”
“s” or “saturation”
“a” or “absolute”
“default”: Ignore the intent of the input image.
“none”: Request that no rendering intent be written.
-inputcs
Assume the input image is in the given colorspace. This is intended to be
used in case IW cannot correctly figure out the colorspace automatically.
Although it can be used to apply a gamma-correction operation to the image,
that’s not really what it’s intended for.
-nogamma
Disable all color correction.
The main purpose of this option is to let you try to replicate what some
other applications might do.
Note that there are many wrong ways to handle color correction, and this
only recreates one of them. For example, some apps might do gamma correction
when the image is read in, but not when it is resized. That’s not what
-nogamma will do.
If you use this with “-grayscale”, you should probably also use “-gsf c”.
This does not affect the colorspace label that will be written to the output
file. If a label is written, it may not be the label you want.
-nocslabel
Do not write a colorspace label to the output image file (if applicable).
This does not affect the image processing.
May be useful for dealing with defective web browsers (I’m looking at
you, Firefox) that display sRGB image colors differently than they
display sRGB CSS/HTML colors.
-density
-density
Control how the density label (i.e. pixels per inch) of the output image is
calculated.
Density policies available:
“auto”: The default. Currently, writes a density only if the image size is
not being changed.
“none”: Do not write a density.
“keep”: Use the same density as the source image.
“adjust”: Adjust the density so that the target image is the same physical
size as the source image.
Instead of a policy, you can request a specific density. Use “i” for pixels
per inch, or “c” for pixels per centimeter. For example, use
“-density i300” for 300 dpi.
This is limited by the target image format’s support for a density labels.
Some formats do not support them, while others require them.
-translate [s]
Move the entire image by the given amount, measured in target pixels. This
is mainly intended for use with -imagesize, or for fine-tuning the image’s
position relative to the pixel grid.
Note that x and y do not have to be integers.
If you use the “s” prefix, the measurements are in source pixels instead of
target pixels.
-offset
-offsetvred -offsetvgreen -offsetvblue -offsetvrb)
While scaling the image, shift the position of a color channel by n output
pixels. A fractional number of pixels is allowed.
The options containing “v” shift the channel vertically; the others shift
it horizontally.
The “rb” options shift the red channel by the amount you specify, and the
blue channel in the opposite direction by the same amount.
Transparency is incompatible with this feature. If there’s any chance your
image has transparency, you should also use -bkgd. Otherwise, IW will
select a background color that you probably won’t like.
Checkerboard backgrounds are currently not supported when -offsetX is used.
-randseed
n is either an integer or the letter “r”.
The seed to use if IW needs to generate random numbers.
“r” means to use a different random seed every time.
Default is 0.
-compress
Suggest the data compression method to use when writing the image.
Recognized options:
“none”
“zip”
“lzw”
“jpeg”
“rle”
The MIFF format supports “zip” (the default) and “none”.
The BMP format supports “rle” and “none” (the default). RLE compression
will only be used if the number of colors is 256 or fewer.
For all other formats, this option currently has no effect.
-colortype
Deprecated. Use “-opt jpeg:colortype=
-interlace
Write an interlaced PNG image, or a progressive JPEG image.
-noopt
Disable a class of image storage optimizations. This option can be used
more than once, to disable multiple optimizations.
This is based on the properties of the unoptimized output image, not on
the properties of the input image.
Optimization names:
“grayscale”: Do not reduce color images to grayscale, even if all pixels
are gray.
“palette”: Never convert to a paletted image.
“reduceto8”: Do not reduce an image with a bit depth of 16 to one with a
bit depth of 8, even if it can be done losslessly.
“stripalpha”: Do not strip a superfluous alpha channel, or use binary or
palette-based transparency.
“binarytrns”: Never use binary (color-keyed) transparency.
“all”: All of the above.
-page
Select the page to read from a multi-page file. The first page is number 1.
Currently, this only works with GIF files. It does not play through the GIF
animation, so you might only get a partial image.
-opt
Set a format-specific option. The syntax may be slightly inconvenient, but
it allows for a large number of options to exist, without much trouble.
Note that you will not get any warnings if you use an unrecognized option.
Options:
“bmp:version=
(Windows BMP v2, also known as OS/2 BMP v1), and “3” (the default; the
standard version that’s compatible with almost everything), “5” (supports
transparency), and “auto” (v5 if needed for transparency, otherwise v3).
“deflate:cmprlevel=
zip/deflate/zlib compression. This applies to all PNG files, and to MIFF
files that use zip compression.
Values range from 0 (no compression) to 9 (best, slowest).
“-1” can be used to mean “default”, but the exact meaning of this is not
well-defined.
“jpeg:arith”: When writing a JPEG file, use arithmetic coding instead of
Huffman coding. This reduces the file size by about 5 to 10% for free,
but many image viewers don’t support JPEG files with arithmetic coding.
“jpeg:bgycc”: Enable libjpeg’s “big gamut YCC” mode. (For experimental use
only.)
“jpeg:block=
experimental use only.)
“jpeg:colortype=
image. This option is recommended for experts only.
JPEG color types:
“rgb”: If a color image is written to a JPEG file, leave it in RGB
format instead of converting it to YCbCr. The resulting file will
likely be larger and less portable.
“rgb1”: Use libjpeg’s “reversible color transform” feature. (For
experimental use only.)
“ycbcr”: Convert color JPEG images to YCbCr (the default).
“jpeg:optcoding”: Enable libjpeg’s “optimize_coding” feature, which makes
the output JPEG file slightly smaller in most cases.
“jpeg:quality=
written. Default is (probably) 75.
“jpeg:rstm=
“MCUs”.
“jpeg:rstr=
“MCU rows”.
“jpeg:sampling=
is written. For example, 2 means the chroma channels will have 1/2 as
many samples as the luma channel. For highest quality, use “1,1”. The
default depends on the “jpeg:quality” setting. Each factor must be
between 1 and 4. Not all combinations are allowed.
“webp:quality”: WebP-style quality setting to use if a WebP file is
written. This is on a scale from 0 to 100. Default is 80.
-includescreen
-noincludescreen
By default, a GIF image will be painted onto the GIF “screen”. Use
-noincludescreen to extract just the individual image.
-zipcmprlevel
Deprecated. Same as “-opt deflate:cmprlevel=
-jpegquality
Deprecated. Same as “-opt jpeg:quality=
-jpegsampling
Deprecated. Same as “-opt jpeg:sampling=
-jpegarith
Deprecated. Same as “-opt jpeg:arith”.
-bmpversion
Deprecated. Same as “-opt bmp:version=
-bmptrns
Attempt to write a BMP image with transparency. Refer to technical.txt for
more information.
-webpquality
Deprecated. Same as “-opt webp:quality=
-encoding
Set the encoding used for text output (informational and error messages).
This is usually unnecessary, because IW can usually figure out what
encoding to use. However, it may be useful if you’re capturing or
redirecting the output, or using a nonstandard terminal program.
Encoding names:
“auto”: The default. On Windows, write Unicode text if writing to a
console; otherwise write UTF-8. On non-Windows systems, try to detect
whether to use UTF-8 or US-ASCII.
“ascii”: US-ASCII
“utf8”: UTF-8
“utf16”: (Windows only.) Write Unicode text if writing to a console;
otherwise write little-endian UTF-16.
-noinfo
Suppress informational messages.
-nowarn
Suppress warnings.
-quiet
Suppress informational messages and warnings.
-version
Display the version number of IW, and of the libraries it uses.
-help
Display a brief help message.
— End —