Technical concepts for graphic design production 4

Raster Image Processing
(raster Graphics)
(3)
Dr. Ahmed Attia
2019
Technical Concepts For
Graphic Design Production

Topics
- Color Gamut.
- Color depth.
- Color Mode.
- Files Formats.

  The entire range of colors available on a particular device
such as a monitor or printer. A monitor, which displays RGB
signals, typically has a greater color gamut than a printer,
which uses CMYK inks.
  Every color system (monitor, desktop printer, digital press,
etc.) has its own unique color gamut.
  gamut. Color gamut is the range of colors and tones
achievable by an imaging system.
What is Color Gamut?. -1

  The color gamut of a computer screen is determined by the
purity and brightness of its red, green and blue pixels.
  The color gamut of a printing device is determined by the
hue, saturation, and lightness of its cyan, magenta, yellow,
and black inks and the brightness and other characteristics
of the paper or substrate on which they are printed.

  Successful designers work within the available color gamut –
or accept some loss of color in the final output.
  For example, if you view your design in RGB without CMYK
soft proofing, chances are you will be disappointed when it
prints.
  Likewise, don’t expect the same color gamut on newsprint as
you can get on commercial offset paper.

  Computer monitors typically have larger color gamut (16.8
Million colors) than printing devices, especially in deep
blues and blacks .(the range is between 4000 – 6000 colors)
for digital printing when we print on coated paper. Also,
When we print on news paper the range is between 2000 -
2500 colors.
  This means the printed result will often be less dramatic than
the original RGB image viewed on screen.
Displaying RGB as CMYK:
Your Monitor is a Variable

CMYK VS RGB on the screen
CMYKRGB

  Computer monitors emit color as RGB (red, green, blue) light.
  Although all colors of the visible spectrum can be produced by
merging red, green and blue light, monitors are capable of
displaying only a limited gamut (i.e., range) of the visible
spectrum.
  Whereas monitors emit light, inked paper absorbs or reflects
specific wavelengths.
  Cyan, magenta and yellow pigments serve as filters,
subtracting varying degrees of red, green and blue from white
light to produce a selective gamut of spectral colors.
CMYK versus RGB color spectrum

  Like monitors, printing inks also produce a color gamut that
is only a subset of the visible spectrum, although the range
is not the same for both.
  Consequently, the same art displayed on a computer
monitor may not match to that printed in a publication.
  Also, because printing processes such as offset lithography
use CMYK (cyan, magenta, yellow, black) inks, digital art
must be converted to CMYK color for print.

Red, Green, Blue –
Additive colors
Cyan, Magenta, Yellow -
Subtractive colors

CMYK - Process Colors for printing

  Pixels are the basic elements that make up a bitmap image.
  Pixels actually have no shape or form until they are viewed,
printed, or otherwise “rendered.”
  Instead, they are little points that contain information in the form
of binary digits or “bits” (ones and zeros — a “0” represents
something, a “1” represents nothing or empty space).
  Bits are the smallest unit of digital information.
  A 1-bit image is the lowliest of all bitmaps. There are only two
digits to work with— a 1 and a 0, which means that each picture
element is either on or off, black or white (I’m keeping this to a
simple one-color example to start with).
Pixels and Color Depth

Color Depth – 1Bit
Black and White

  But a 2-bit image is much more detailed. Now you have four
possibilities or values for each pixel: 00, 01, 10, 11 (black,
white, and two shades of gray).
Color Depth –2 Bits - greys

Color Depth – 2 Bits - greys

  three bits yields eight values, four bits 16, eight bits 256, and so on.
  In mathematical terms, this is called the power of two: 22 equals four
choices (2 × 2), 28 is 256 choices (2 × 2 × 2 × 2 × 2 × 2 × 2 × 2).
Generally speaking, a one-color digital image needs to be at least 8-
bit (256 tones).
  So far, we’ve only talked about bits in terms of black, white, or gray.
  Since most people work in color, you now have to apply the same
thinking to each color component of the image.
  So, in a 24-bit (8 bits per color) RGB image, there are 256 possible
values of Red,256 of Green, and 256 of Blue, for a grand total? —
16,777,216 possible values, tones, or colors for each pixel.
Color Depth – 8 Bits

  So, in a 24-bit (8 bits per color) RGB image, there are 256
possible values of Red,256 of Green, and 256 of Blue, for a
grand total? —16,777,216 possible values, tones, or colors for
each pixel.
  A CMYK color image is described as 32-bit, or one 8-bit
channel for each of the four printing colors: cyan, magenta,
yellow, and black or “K.”
  There is no more color information with CMYK; it’s just
allocated differently than RGB.

Color Depth For RGB – 24 Bits

  Whether an image has one, two, four, eight, or even more bits
of information per pixel per color determines its bit depth.
  The higher the bit depth, the more detailed and realistic the
image.
  We don’t have to stop at 8 bits. Current input technology
allows for up to 16 bits of information per channel.

Color Depth For CMYK– 32 Bits

 An 8-bit image can have 28 = 256 tones
 A 24-bit image can have about 16.8 million tones
 A 32-bit image can have about 4.3 billion tones
Conclusion For Color depth values

Comparison between
color depth values

Comparison between
color depth values
8 Bits 1 Bits

  Bitmap mode (2 colors).
  Grayscale mode (256 grays).
  RGB mode (millions of colors).
  CMYK mode (four-printed colors).
  Duotone mode (as the number of the channels).
Different Color Modes

Bitmap Greyscale RGB CMYK Duotone
Different Color Modes

  Bitmap mode uses one of two color values (black or white)
to represent the pixels in an image.
  Images in Bitmap mode are called bitmapped 1‑bit images
because they have a bit depth of 1.
Bitmap Mode

Line Art High resolution 600 – 1200 ppi

  Grayscale mode uses different shades of gray in an image.
  In 8‑bit images, there can be up to 256 shades of gray.
  Every pixel of a grayscale image has a brightness value
ranging from 0 (black) to 255 (white).
  In 16-and 32‑bit images, the number of shades in an image is
much greater than in 8‑bit images.
  Grayscale values can also be measured as percentages of
black ink coverage (0% is equal to white, 100% to black).
Greyscale Mode

Converted image from RGB mode to
Greyscale Mode

  for images in web or e-mail to reduce file size while maintaining
color integrity.
  Photoshop RGB Color mode uses the RGB model, assigning an
intensity value to each pixel. In 8‑bits-per-channel images, the
intensity values range from 0 (black) to 255 (white) for each of
the RGB (red, green, blue) components in a color image.
  RGB images use three colors, or channels, to reproduce colors on
screen. In 8‑bits-per-channel images, the three channels
translate to 24 (8 bits x 3 channels) bits of color information per
pixel.
RGB Mode -1

  With 24‑bit images, the three channels can reproduce up to
16.7 million colors per pixel.
  With 48‑bit (16‑bits-per-channel) and 96‑bit (32‑bits-per-
channel) images, even more colors can be reproduced per
pixel.
  In addition to being the default mode for new Photoshop
images, the RGB model is used by computer monitors to
display colors.
RGB Mode -3

  In the CMYK mode, each pixel is assigned a percentage
value for each of the process inks.
  The lightest (highlight) colors are assigned small percentages
of process ink colors; the darker (shadow) colors higher
percentages.
  For example, a bright red might contain 2% cyan, 93%
magenta, 90% yellow, and 0% black.
  In CMYK images, pure white is generated when all four
components have values of 0%.
CMYK Mode -1

  In the CMYK mode, each pixel is assigned a percentage
value for each of the process inks.
  The lightest (highlight) colors are assigned small percentages
of process ink colors; the darker (shadow) colors higher
percentages.
  For example, a bright red might contain 2% cyan, 93%
magenta, 90% yellow, and 0% black.
  In CMYK images, pure white is generated when all four
components have values of 0%.
CMYK Mode -3

  Use the CMYK mode when preparing an image to be printed
using process colors.
  Converting an RGB image into CMYK creates a color separation.
  If you start with an RGB image, it’s best to edit first in RGB and
then convert to CMYK at the end of your editing process.
  In RGB mode, you can use the Proof Setup commands to
simulate the effects of a CMYK conversion without changing the
actual image data.
  You can also use CMYK mode to work directly with CMYK images
scanned or imported from high-end systems.
CMYK Mode -4

  Duotone mode creates monotone, duotone (two-color), triton
(three-color), and quad tone (four-color) grayscale images
using one to four custom inks.
Duotone Mode

Grayscale
Duotone Image
Comparison between Duotone and grayscale

Graphic File Formats For
Raster graphics

PSD
TIFF
EPS
DCS1
DCS2
PDF
JPEG
Graphic File Formats For
Raster graphics

  PSD is a proprietary layered image format that stands for
Photoshop Document.
  These are original design files created in Photoshop that are
fully editable with multiple layers and image adjustments.
  PSDs are primarily used to create and edit raster images, but
this unique format can also contain vector layers as well,
making it extremely flexible for a number of different projects.
  A PSD can be exported into any number of image file formats,
including all of the raster formats listed above.
PSD Format

  (Tagged-Image File Format) — A large raster file. It is used
when a high resolution photographic file is needed.
  Typically used for print production.
  TIFF is a lossless raster format that stands for Tagged Image File
Format. Because of its extremely high quality, the format is
primarily used in photography and desktop publishing.
  You’ll likely encounter TIFF files when you scan a document or
take a photo with a professional digital camera.
  Do note that TIFF files can also be used as a “container” for
JPEG images. These files will be much smaller than traditional
TIFF files, which are typically very large.
TIFF Format -1

  The TIFF format was originally developed by the Aldus
Corporation, and was intended primarily for use in scanning
and desktop publishing.
  Aldus first published the specification in 1986. When Adobe
Systems Incorporated purchased Aldus in 1994, they acquired
the rights to the TIFF specification, and have maintained it
since then.
  The current version of the specification (revision 6.0) was
released in 1992.
TIFF Format -2

  TIFF supports color depths from 1- bit to 24- bit (e.g.
monochrome to true color), and a wide range of compression
types (RLE, LZW, CCITT Group 3 and Group 4, and JPEG), as
well as uncompressed data.
  Adobe owns the TIFF specification, but makes it freely
available for use.
  TIFF is one of the most flexible, popular and widely supported
raster formats in use today.
TIFF Format -3

  Encapsulated PostScript (EPS) language file format can contain both vector
and bitmap graphics and is supported by virtually all graphics, illustration,
and page-layout programs.
  EPS format is used to transfer PostScript artwork between applications.
  When you open an EPS file containing vector graphics, Photoshop rasterizes
the image, converting the vector graphics to pixels.
  EPS format supports Lab, CMYK, RGB, Indexed Color, Duotone, Grayscale,
and Bitmap color modes, and does not support alpha channels.
  Desktop Color Separations (DCS) format, a version of the standard EPS format,
lets you save color separations of CMYK images.
Photoshop EPS Format -1

  You use DCS 2.0 format to export images containing spot channels.
  To print EPS files, you must use a PostScript printer.
  it is a large raster file similar to a TIFF file.
  EPS is an image format that stands for Encapsulated PostScript.
  Although it is used primarily as a vector format, an EPS file can
include both vector and raster image data.
  Typically, an EPS file includes a single design element that can be
used in a larger design.
Photoshop EPS Format -2

  Desktop Color Separations (DCS) format is a version of the
standard EPS format that lets you save color separations of
CMYK images (Master + 4 files).
  You can use DCS 2.0 format to export images containing
spot channels.
  To print DCS files, you must use a PostScript printer.
DCS1 and DCS2 Formats

  A DCS 1 file is composed of 5 separate files.
  As you see in the figure:- the main file has the extension eps while the 4
other files have an extension that marks the color data they contain.
  The file size shows that the main file does not contain any actual image
data but only a preview image and pointers to the other 4 corresponding
higher files.
  Because the main file has lines in it that refer to the other files, you cannot
simply rename DCS-files in the Macintosh Finder or Windows Explorer.
  If you want to change the name of a DCS-file, it is best to open it in
Photoshop and use a SAVE AS to save the file using a different name.
DCS1 Format

  PDF stands for Portable Document Format and is an image format
used to display documents and graphics correctly, no matter the
device, application, operating system or web browser.
  At its core, PDF files have a powerful vector graphics foundation,
but can also display everything from raster graphics to form fields
to spreadsheets.
  Because it is a near universal standard, PDF files are often the file
format requested by printers to send a final design into
production.
  Both Adobe Photoshop and Illustrator can export straight to PDF,
making it easy to start your design and get it ready for printing.
PDF – Portable Document Format

  (Joint Photographic Experts Group) — A compressed raster
file. It is used when a small photographic file is needed
(typically for the Web).
  JPG files can be created at a variety of compression levels.
More compression equals less quality.
  It is important to know the resolution of a JPG file to determine
if the image is of high enough quality to be used for print
production.
  So, We can not use it to save the image files, which We will
use it in printing products.
JPEG Format -1

  JPGs can be optimized, when saving them out of Photoshop,
to find the perfect balance of small file size and high quality.
  On the web, you want your images files to be as small as they
can be so your site loads quickly, but large enough to still
appear crisp and not pixilated.
  A JPG can’t have a transparent background so they are
always in the shape of a rectangle or square with a solid
background.
JPEG Format -2

  https://www.pcmag.com/encyclopedia/term/39985/color-gamut
  http://www.printernational.org/rgb-versus-cmyk.php
  https://www.slrlounge.com/color-depth-affects-image-quality/
  https://www.slrlounge.com/color-depth-affects-image-quality/
  https://wolfcrow.com/blog/what-is-color-color-bit-depth-and-a-color-
model/
  http://paulbourke.net/dataformats/bitmaps/
  https://helpx.adobe.com/photoshop/using/color-modes.html
  http://www.graphic-design-employment.com/color-mode.html
  https://modassicmarketing.com/understanding-image-file-types
  https://99designs.com/blog/tips/image-file-types/#PSD
  https://helpx.adobe.com/photoshop/using/file-formats.html
References

Technical concepts for graphic design production 4

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