Re: Does InDesign change image format like Word does?

["Fred Ridder" <docudoc -at- hotmail -dot- com>]

I'm sure that is not what Joanne meant, because if so she
would be at least partly incorrect.

In the world of raster images, resolution is the number of pixels
in the image, and is essentially independent from the tool used
to make the image file and the file format used for the image.
When you make a screen capture, the capture tool generally
allows you to specify the resolution (in pixels per inch) or else
will use the Windows default resolution of 96 pixels per inch.
If you are saving or reusing a copy of an existing raster image,
you do not want to do anything that tries to change the
number of pixels (technically known as resampling) because
this inevitably degrades the image quality. If you need to
change the reproduced size of the image, the proper way
to do it is to change the dpi setting at which the image is
displayed and/or printed.

Another "dimension" of raster images is the color depth, which
refers to how many bits are used to define the color of each
pixel. More bits per pixel means finer, more accurate gradation
of colors. Most image file formats use a direct encoding scheme
with an equal number of bits allocated to define the red, blue,
and green intensity of the each pixel. 24-bit color depth (8
bits per color) is generally the standard for photographic images
and can theoretically define more than 16 million "different"
colors (256 red intensities x 256 green x 256 blue). But the
\downside is file size, since each pixel requires three bytes
of data; 3 megapixel at 24-bit color depth means 9 MB of data.
The GIF file format reduces the size of image files by limiting
the number of colors to 256 (8 bits) per pixel, but the trick it
uses is to use a lookup table to index those 8-bit color numbers
to 256 specific colors that are defined with greater accuracy.
And this all ignores the issues of the computer's RGB color
space vs. the offset printing world's CMYK color space, which
Joann raised in here message.

A more subtle difference between image file formats is
whether it uses any form of idata compression. Some formats
are uncompressed, which means large (or very large) file sizes.
Some use a lossless form of compression called run-length
encoding (or RLE, which is also used in fax), which encodes
the color value for a run of identical-color pixels on the same
line only once, along with a parameter that defines the number
of pixels in the run. Some file formats use a mathematical
algorithm for lossless data compression (LZW algorithm being
the most popular. And at least one file formats--JPEG--uses
a lossy form of compression that relies on the properties
of a certain type of image, namely photographic images, which
generally have large percentages of image area where it will
not be noticeable if some image detail gets thrown away by
the compression algorithm.

Here are highly simplified descriptions of some of the most
common raster image file formats:

BMP is an old, non-compressed image file format that is specific
to Windows. Files are large and not portable to other platforms.

TIFF is also an old file format, and ius supported on all popular
platforms, although it exists in at least a half-dozen different
variations not all of which are interchangeable. In TIFF, the
image itself is not compressed, but the file may use lossless
LZW compression to compress the data after the fact. And
TIFF can support either RGB or CMYK color spaces.

GIF is a well-established file format that provides excellent
portability and very compact file size through use of RLE
image compression, a color palette with 256 indexed colors,
and LZW data compression. The indexed color scheme works
fine for most technical line art, but is not adequate for
full-color or photographic images and is strictly limited to
the RGB color space.

PNG is a more modern version of GIF. It can use either a
palette-indexed color scheme or directly encoded colors,
and supports a "alpha channel" to support transparent colors,
but does not support the CMYK color space since it is
intended for web applications.

JPEG is a modern file format that was specifically designed
for *photographic* images (the "P" in JPEG stands for
"photographic") and is *not* appropriate for line art or
images containing text. JPEG does have several different
quality levels (higher quality meaning lower rates of image
compression), but because the compression algorithm
works with clumps of adjacent pixels it inherently produces
artifacts (what you might call "smudginess") near sharp
edges and abrupt color transitions in the image. (The
Wikipedia article on PNG has a side-by-side comparison
of PNG and JPEG which very effectively shows this effect.)
And because the JPEG algorithm is lossy, every time you
edit and resave a JPEG image, the image quality goes
down another notch

Beyond the raster image file formats, this thread has also
touched on at least one meta-file format, EPS, which can
contain vector content (e.g. editable text and drawing
elements) as well as raster image data. EPS is a fairly
inefficient way of handling raster-only images, but is the
right choice if the image contains any vector content
(e.g. if it is an editable line drawing or a raster image with
callouts added to it). Using a raster file format for a graphic
that contains vector elements throws away the editability
of the vector content.

I hope some of this helps.

My opinions only; I don't speak for Intel.
Fred Ridder
Intel
Parsippany, NJ

>From: "Kathleen MacDowell" <kathleen -at- writefortheuser -dot- com>
>To: "Joanne Wittenbrook" <jwittenbrook -at- ameritech -dot- net>
>CC: techwr-l -at- lists -dot- techwr-l -dot- com
>Subject: Re: Does InDesign change image format like Word does?
>Date: Fri, 9 Mar 2007 19:35:52 -0600
>
>Thanks, Joanne, great information. Are you saying that jpg and tiff are
>better resolution and for InDesign?
>
>
>On 3/9/07, Joanne Wittenbrook <jwittenbrook -at- ameritech -dot- net> wrote:
> >
> > ----------------------------------
> > >I can't answer your questions in general, but from experience, InDesign
> > >seems to like .eps files better than .bmp. So you might save the Snagit
> > >file
> > >before importing it into InDesign.
> > ---------------------------------------------
> >
> >
> > No. Word is an Office program, designed for people who are not going to
> > take a document to an actual printing press. Office programs use the RGB
> > color space because monitors use it and most office printers translate 
>it on
> > output. In the average business application, color accuracy is not a
> > concern. The goal is pleasing and bright color.
> >
> > InDesign is a page layout program. The usual work flow is for the images
> > and text to be created in other programs. Illustrator or Photoshop for
> > images, word processors for text. The content is imported into frames in
> > InDesign for formatting and manipulating, pagination, indexing etc.
> >
> > BMP is a pretty old format. To have enough resolution to successfully
> > print, it will be a large file. JPEGs or TIFFs have a greater capacity 
>to
> > compress color information and are less likely to degrade the color 
>quality.
> > Programs like InDesign are set up for using the CMYK (cyan, magenta, 
>yellow,
> > black) color space because that is the ink colors used by an offset 
>press to
> > print color.
> >
> > InDesign does not "change" images. It is designed for an end user that
> > understands graphic arts and printing. Frequently InDesign users will 
>import
> > a low resolution image for position to keep file size down while they 
>are
> > designing. When the file goes to the printer the high resolution image 
>is
> > sent with it and swapped into the file during prepress operations.
> >
> > The basic Microsoft suite is designed for the Office user with no
> > particular expertise in print or color management. Microsoft makes the
> > decision on image format for you because they assume you are not 
>concerned
> > with that aspect of the document.
> > Joanne
> > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >
> >
> > --
> > Kathleen MacDowell
> > www.writefortheuser.com
>^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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