Alien-FreeImage

 view release on metacpan or  search on metacpan

src/Source/LibJPEG/usage.txt  view on Meta::CPAN

			view an arithmetic coded JPEG file at all.

	-block N	Set DCT block size.  All N from 1 to 16 are possible.
			Default is 8 (baseline format).
			Larger values produce higher compression,
			smaller values produce higher quality
			(exact DCT stage possible with 1 or 2; with the
			default quality of 75 and default Luminance qtable
			the DCT+Quantization stage is lossless for N=1).
			CAUTION: An implementation of the JPEG SmartScale
			extension is required for this feature.  SmartScale
			enabled JPEG is not yet widely implemented, so many
			decoders will be unable to view a SmartScale extended
			JPEG file at all.

	-rgb1		Create RGB JPEG file with reversible color transform.
			Works like the -rgb switch (see above) and inserts a
			simple reversible color transform into the processing
			which significantly improves the compression.
			Use this switch in combination with the -block N
			switch (see above) for lossless JPEG coding.
			CAUTION: A decoder with inverse color transform
			support is required for this feature.  Reversible
			color transform support is not yet widely implemented,
			so many decoders will be unable to view a reversible
			color transformed JPEG file at all.

	-bgycc		Create big gamut YCC JPEG file.
			In this type of encoding the color difference
			components are quantized further by a factor of 2
			compared to the normal Cb/Cr values, thus creating
			space to allow larger color values with higher
			saturation than the normal gamut limits to be encoded.
			In order to compensate for the loss of color fidelity
			compared to a normal YCC encoded file, the color
			quantization tables can be adjusted accordingly.
			For example, cjpeg -bgycc -quality 80,90 will give
			similar results as cjpeg -quality 80.
			CAUTION: For correct decompression a decoder with big
			gamut YCC support (JFIF version 2) is required.
			An old decoder may or may not display a big gamut YCC
			encoded JPEG file, depending on JFIF version check
			and corresponding warning/error configuration.
			In case of a granted decompression the old decoder
			will display the image with half saturated colors.

	-dct int	Use integer DCT method (default).
	-dct fast	Use fast integer DCT (less accurate).
	-dct float	Use floating-point DCT method.
			The float method is very slightly more accurate than
			the int method, but is much slower unless your machine
			has very fast floating-point hardware.  Also note that
			results of the floating-point method may vary slightly
			across machines, while the integer methods should give
			the same results everywhere.  The fast integer method
			is much less accurate than the other two.

	-nosmooth	Don't use high-quality downsampling.

	-restart N	Emit a JPEG restart marker every N MCU rows, or every
			N MCU blocks if "B" is attached to the number.
			-restart 0 (the default) means no restart markers.

	-smooth N	Smooth the input image to eliminate dithering noise.
			N, ranging from 1 to 100, indicates the strength of
			smoothing.  0 (the default) means no smoothing.

	-maxmemory N	Set limit for amount of memory to use in processing
			large images.  Value is in thousands of bytes, or
			millions of bytes if "M" is attached to the number.
			For example, -max 4m selects 4000000 bytes.  If more
			space is needed, temporary files will be used.

	-verbose	Enable debug printout.  More -v's give more printout.
	or  -debug	Also, version information is printed at startup.

The -restart option inserts extra markers that allow a JPEG decoder to
resynchronize after a transmission error.  Without restart markers, any damage
to a compressed file will usually ruin the image from the point of the error
to the end of the image; with restart markers, the damage is usually confined
to the portion of the image up to the next restart marker.  Of course, the
restart markers occupy extra space.  We recommend -restart 1 for images that
will be transmitted across unreliable networks such as Usenet.

The -smooth option filters the input to eliminate fine-scale noise.  This is
often useful when converting dithered images to JPEG: a moderate smoothing
factor of 10 to 50 gets rid of dithering patterns in the input file, resulting
in a smaller JPEG file and a better-looking image.  Too large a smoothing
factor will visibly blur the image, however.

Switches for wizards:

	-baseline	Force baseline-compatible quantization tables to be
			generated.  This clamps quantization values to 8 bits
			even at low quality settings.  (This switch is poorly
			named, since it does not ensure that the output is
			actually baseline JPEG.  For example, you can use
			-baseline and -progressive together.)

	-qtables file	Use the quantization tables given in the specified
			text file.

	-qslots N[,...] Select which quantization table to use for each color
			component.

	-sample HxV[,...]  Set JPEG sampling factors for each color component.

	-scans file	Use the scan script given in the specified text file.

The "wizard" switches are intended for experimentation with JPEG.  If you
don't know what you are doing, DON'T USE THEM.  These switches are documented
further in the file wizard.txt.


DJPEG DETAILS

The basic command line switches for djpeg are:

	-colors N	Reduce image to at most N colors.  This reduces the
	or -quantize N	number of colors used in the output image, so that it
			can be displayed on a colormapped display or stored in
			a colormapped file format.  For example, if you have
			an 8-bit display, you'd need to reduce to 256 or fewer
			colors.  (-colors is the recommended name, -quantize
			is provided only for backwards compatibility.)

	-fast		Select recommended processing options for fast, low
			quality output.  (The default options are chosen for
			highest quality output.)  Currently, this is equivalent
			to "-dct fast -nosmooth -onepass -dither ordered".

src/Source/LibJPEG/usage.txt  view on Meta::CPAN

	-os2		Select BMP output format (OS/2 1.x flavor).  8-bit
			colormapped format is emitted if -colors or -grayscale
			is specified, or if the JPEG file is gray-scale;
			otherwise, 24-bit full-color format is emitted.

	-pnm		Select PBMPLUS (PPM/PGM) output format (this is the
			default format).  PGM is emitted if the JPEG file is
			gray-scale or if -grayscale is specified; otherwise
			PPM is emitted.

	-rle		Select RLE output format.  (Requires URT library.)

	-targa		Select Targa output format.  Gray-scale format is
			emitted if the JPEG file is gray-scale or if
			-grayscale is specified; otherwise, colormapped format
			is emitted if -colors is specified; otherwise, 24-bit
			full-color format is emitted.

Switches for advanced users:

	-dct int	Use integer DCT method (default).
	-dct fast	Use fast integer DCT (less accurate).
	-dct float	Use floating-point DCT method.
			The float method is very slightly more accurate than
			the int method, but is much slower unless your machine
			has very fast floating-point hardware.  Also note that
			results of the floating-point method may vary slightly
			across machines, while the integer methods should give
			the same results everywhere.  The fast integer method
			is much less accurate than the other two.

	-dither fs	Use Floyd-Steinberg dithering in color quantization.
	-dither ordered	Use ordered dithering in color quantization.
	-dither none	Do not use dithering in color quantization.
			By default, Floyd-Steinberg dithering is applied when
			quantizing colors; this is slow but usually produces
			the best results.  Ordered dither is a compromise
			between speed and quality; no dithering is fast but
			usually looks awful.  Note that these switches have
			no effect unless color quantization is being done.
			Ordered dither is only available in -onepass mode.

	-map FILE	Quantize to the colors used in the specified image
			file.  This is useful for producing multiple files
			with identical color maps, or for forcing a predefined
			set of colors to be used.  The FILE must be a GIF
			or PPM file.  This option overrides -colors and
			-onepass.

	-nosmooth	Don't use high-quality upsampling.

	-onepass	Use one-pass instead of two-pass color quantization.
			The one-pass method is faster and needs less memory,
			but it produces a lower-quality image.  -onepass is
			ignored unless you also say -colors N.  Also,
			the one-pass method is always used for gray-scale
			output (the two-pass method is no improvement then).

	-maxmemory N	Set limit for amount of memory to use in processing
			large images.  Value is in thousands of bytes, or
			millions of bytes if "M" is attached to the number.
			For example, -max 4m selects 4000000 bytes.  If more
			space is needed, temporary files will be used.

	-verbose	Enable debug printout.  More -v's give more printout.
	or  -debug	Also, version information is printed at startup.


HINTS FOR CJPEG

Color GIF files are not the ideal input for JPEG; JPEG is really intended for
compressing full-color (24-bit) images.  In particular, don't try to convert
cartoons, line drawings, and other images that have only a few distinct
colors.  GIF works great on these, JPEG does not.  If you want to convert a
GIF to JPEG, you should experiment with cjpeg's -quality and -smooth options
to get a satisfactory conversion.  -smooth 10 or so is often helpful.

Avoid running an image through a series of JPEG compression/decompression
cycles.  Image quality loss will accumulate; after ten or so cycles the image
may be noticeably worse than it was after one cycle.  It's best to use a
lossless format while manipulating an image, then convert to JPEG format when
you are ready to file the image away.

The -optimize option to cjpeg is worth using when you are making a "final"
version for posting or archiving.  It's also a win when you are using low
quality settings to make very small JPEG files; the percentage improvement
is often a lot more than it is on larger files.  (At present, -optimize
mode is always selected when generating progressive JPEG files.)

GIF input files are no longer supported, to avoid the Unisys LZW patent
(now expired).
(Conversion of GIF files to JPEG is usually a bad idea anyway.)


HINTS FOR DJPEG

To get a quick preview of an image, use the -grayscale and/or -scale switches.
"-grayscale -scale 1/8" is the fastest case.

Several options are available that trade off image quality to gain speed.
"-fast" turns on the recommended settings.

"-dct fast" and/or "-nosmooth" gain speed at a small sacrifice in quality.
When producing a color-quantized image, "-onepass -dither ordered" is fast but
much lower quality than the default behavior.  "-dither none" may give
acceptable results in two-pass mode, but is seldom tolerable in one-pass mode.

If you are fortunate enough to have very fast floating point hardware,
"-dct float" may be even faster than "-dct fast".  But on most machines
"-dct float" is slower than "-dct int"; in this case it is not worth using,
because its theoretical accuracy advantage is too small to be significant
in practice.

Two-pass color quantization requires a good deal of memory; on MS-DOS machines
it may run out of memory even with -maxmemory 0.  In that case you can still
decompress, with some loss of image quality, by specifying -onepass for
one-pass quantization.

To avoid the Unisys LZW patent (now expired), djpeg produces uncompressed GIF
files.  These are larger than they should be, but are readable by standard GIF
decoders.

src/Source/LibJPEG/usage.txt  view on Meta::CPAN

If more space is needed than will fit in the available main memory (as
determined by -maxmemory), temporary files will be used.  (MS-DOS versions
will try to get extended or expanded memory first.)  The temporary files are
often rather large: in typical cases they occupy three bytes per pixel, for
example 3*800*600 = 1.44Mb for an 800x600 image.  If you don't have enough
free disk space, leave out -progressive and -optimize (for cjpeg) or specify
-onepass (for djpeg).

On MS-DOS, the temporary files are created in the directory named by the TMP
or TEMP environment variable, or in the current directory if neither of those
exist.  Amiga implementations put the temp files in the directory named by
JPEGTMP:, so be sure to assign JPEGTMP: to a disk partition with adequate free
space.

The default memory usage limit (-maxmemory) is set when the software is
compiled.  If you get an "insufficient memory" error, try specifying a smaller
-maxmemory value, even -maxmemory 0 to use the absolute minimum space.  You
may want to recompile with a smaller default value if this happens often.

On machines that have "environment" variables, you can define the environment
variable JPEGMEM to set the default memory limit.  The value is specified as
described for the -maxmemory switch.  JPEGMEM overrides the default value
specified when the program was compiled, and itself is overridden by an
explicit -maxmemory switch.

On MS-DOS machines, -maxmemory is the amount of main (conventional) memory to
use.  (Extended or expanded memory is also used if available.)  Most
DOS-specific versions of this software do their own memory space estimation
and do not need you to specify -maxmemory.


JPEGTRAN

jpegtran performs various useful transformations of JPEG files.
It can translate the coded representation from one variant of JPEG to another,
for example from baseline JPEG to progressive JPEG or vice versa.  It can also
perform some rearrangements of the image data, for example turning an image
from landscape to portrait format by rotation.

jpegtran works by rearranging the compressed data (DCT coefficients), without
ever fully decoding the image.  Therefore, its transformations are lossless:
there is no image degradation at all, which would not be true if you used
djpeg followed by cjpeg to accomplish the same conversion.  But by the same
token, jpegtran cannot perform lossy operations such as changing the image
quality.

jpegtran uses a command line syntax similar to cjpeg or djpeg.
On Unix-like systems, you say:
	jpegtran [switches] [inputfile] >outputfile
On most non-Unix systems, you say:
	jpegtran [switches] inputfile outputfile
where both the input and output files are JPEG files.

To specify the coded JPEG representation used in the output file,
jpegtran accepts a subset of the switches recognized by cjpeg:
	-optimize	Perform optimization of entropy encoding parameters.
	-progressive	Create progressive JPEG file.
	-arithmetic	Use arithmetic coding.
	-restart N	Emit a JPEG restart marker every N MCU rows, or every
			N MCU blocks if "B" is attached to the number.
	-scans file	Use the scan script given in the specified text file.
See the previous discussion of cjpeg for more details about these switches.
If you specify none of these switches, you get a plain baseline-JPEG output
file.  The quality setting and so forth are determined by the input file.

The image can be losslessly transformed by giving one of these switches:
	-flip horizontal	Mirror image horizontally (left-right).
	-flip vertical		Mirror image vertically (top-bottom).
	-rotate 90		Rotate image 90 degrees clockwise.
	-rotate 180		Rotate image 180 degrees.
	-rotate 270		Rotate image 270 degrees clockwise (or 90 ccw).
	-transpose		Transpose image (across UL-to-LR axis).
	-transverse		Transverse transpose (across UR-to-LL axis).

The transpose transformation has no restrictions regarding image dimensions.
The other transformations operate rather oddly if the image dimensions are not
a multiple of the iMCU size (usually 8 or 16 pixels), because they can only
transform complete blocks of DCT coefficient data in the desired way.

jpegtran's default behavior when transforming an odd-size image is designed
to preserve exact reversibility and mathematical consistency of the
transformation set.  As stated, transpose is able to flip the entire image
area.  Horizontal mirroring leaves any partial iMCU column at the right edge
untouched, but is able to flip all rows of the image.  Similarly, vertical
mirroring leaves any partial iMCU row at the bottom edge untouched, but is
able to flip all columns.  The other transforms can be built up as sequences
of transpose and flip operations; for consistency, their actions on edge
pixels are defined to be the same as the end result of the corresponding
transpose-and-flip sequence.

For practical use, you may prefer to discard any untransformable edge pixels
rather than having a strange-looking strip along the right and/or bottom edges
of a transformed image.  To do this, add the -trim switch:
	-trim		Drop non-transformable edge blocks.
Obviously, a transformation with -trim is not reversible, so strictly speaking
jpegtran with this switch is not lossless.  Also, the expected mathematical
equivalences between the transformations no longer hold.  For example,
"-rot 270 -trim" trims only the bottom edge, but "-rot 90 -trim" followed by
"-rot 180 -trim" trims both edges.

If you are only interested in perfect transformation, add the -perfect switch:
	-perfect	Fails with an error if the transformation is not
			perfect.
For example you may want to do
  jpegtran -rot 90 -perfect foo.jpg || djpeg foo.jpg | pnmflip -r90 | cjpeg
to do a perfect rotation if available or an approximated one if not.

We also offer a lossless-crop option, which discards data outside a given
image region but losslessly preserves what is inside.  Like the rotate and
flip transforms, lossless crop is restricted by the current JPEG format: the
upper left corner of the selected region must fall on an iMCU boundary.  If
this does not hold for the given crop parameters, we silently move the upper
left corner up and/or left to make it so, simultaneously increasing the
region dimensions to keep the lower right crop corner unchanged.  (Thus, the
output image covers at least the requested region, but may cover more.)
The adjustment of the region dimensions may be optionally disabled.

The image can be losslessly cropped by giving the switch:
	-crop WxH+X+Y	Crop to a rectangular subarea of width W, height H
			starting at point X,Y.