Staff Development Continuing Education Series:

What we’ll discuss…

Pixels:Resolution and ResizingColor

File formats Hardware & Software

“you say you want a re(s)olution”

Digital Images and Pixels

Digital Images are composed of digital elements called pixels.

Pixels are bundles of digital information about the color of a specific spot in the image.

They are organized into a grid to convey the image.

Patterns of dots produce the effects of consistent color

The size of each pixel is determined by print size.

Digital Images and Pixels

The RESOLUTION is the ratio of the number of PIXELS to the PRINT size.

Resolution = # of pixels on the longest side print size

Resolution is used to judge the quality of the image. Most often measured in pixels (or dots) per inch or ‘ppi’.

The Big Picture

=

Increasing size without increasing resolution stretches out the dots of color.

The Big Picture

=.5 x.75 @ 72dpi;6.5 kb

4 x 5 @ 10 dpi6.5 kb

The Big Picture

=

Resolution SHOULD decrease when you enlarge, but if you scan at a high resolution, the loss won’t be as severe.

The Big Picture

4 x 5 @ 72 dpi113 kb

=

.5 x.75 @ 575dpi;113 kb

Changing the document size alone doesn’t change the pixel dimensions or the file size

Before: 6.569 x 6.694 inches (473x482 pixels)72dpi667.9K

The number of pixels doesn’t change…just the print size of them.

After:3 x 3.057 inches (473x482 pixels)158 dpi667.9K

Resolution

Print-Size

Print-size and resolution are inversely related…

“Resampling” can change the number of pixels, which can therefore change the file size

Before: 6.569 x 6.694 inches (473x482 pixels)72dpi667.9K

After:3 x 3.057 inches (473x482 pixels)72 dpi139.3K

Resampling can be done to any of the variables (print size, number of pixels, or resolution) independently of each other.

Resampling breaks the relationship between the variables. It always results in file size change because I add or take away pixels.

After:6.569 x 6.694 inches (105x107 pixels)35 dpi32.9K

Resolution

Prin

t-S

ize

Resampling breaks the relationship between resolution and print size

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≠

≠

A Warning…

It is possible to resample up or “interpolate”. The computer adds in new dots and guesses their color. The quality is typically poor…

=

4 x 5 @ 72dpi323 kb

.5 x.75 @ 72dpi;6.5 kb

Why Resample?Resampling is used to change image quality for specific purposes…

Print QualityGood consumer printers can print up to about 275 ppi. Commercial printers are often much better.

300 dpi is a print industry standard.

The human eye usually can’t appreciate detail higher than 300 dpi from about 8 inches distance

Monitor Quality

Regardless of the print size you dictate, the monitor will always display 72 pixels in each inch (unless your browser program creates a temporary view).

If you scan something at 300 ppi and show it on a monitor, it will be resized to 72 ppi meaning a 5 inch image would be 21 inches.

These images look as good as print images to your eye because of optical illusion

“16(-bit) and what do you get?”

Painting with Pixels

What are pixels made of? Pixels are a string of code (a series of 0s or

1s) that signify directions for different colors. Each 0 or 1 is called a “bit.” The number of bits in the pixel determines the

color palette.

More bits = more combinations = more possible colors

This is called ‘bit-depth’

Painting with Pixels How does bit-depth affect color?

1-bit = two colors (0 or 1 for each pixel)

2-bit = four colors (00, 11, 01, 10)

4-bit = 16 colors (0000, 0001, 0100, 0101, 0111, etc.)

8-bit = 256 colors (00000000, 001…, 010.. 011..., 001…, 111…)

16-bit = 65,536 colors (00000…, 000…, 0…, 0…, 0…, 0…, 0…)

The more colors you can use, the more realistic a picture looks…and the bigger the file is

Painting with Pixels

Multi-channel Color (RGB) 3 channels (R,G,B) @ 8-bit = 24 bits per pixel

○ 256 kinds of Red…○ 256 kinds of Green…○ 256 kinds of Blue…

Combined to make millions of colors

3 channels (R,G,B) @ 16-bit = 48-bits per pixel = ○ 65, 536 kinds of Red…○ 65,536 kinds of Green…○ 65,536 kinds of Blue…

Combined to make BILLIONS of colors

1-bit, black and white

8-bit grayscale

1-bit, black and white

8-bit grayscale

1-bit, black and white

8-bit grayscale

24-bit color

8-bit grayscale

24-bit color

Which looks better to you?

24-bit color8-bit color

Can you tell the difference here?

8-bit or

24-bit?

Can you tell the

difference here?

24-bit or 48-bit?

Can you tell the

difference here?

Palatable Palettes

The proper color palette to use depends on the image and how you will use it…

Palatable PalettesWhich Color Settings to Use?

1-bit: Black & White text with no artifactual value mainly for large-scale book scanning, ILL

scanning

8-bit, 1 channel: Indexed color or grayscale web graphics and thumbnails, NOT continuous tone images text with some artifactual value; sometimes with black and white images

8-bit, 3 channels (24-bit): RGB manuscript text, photographs, slides, etc.

16-bit, 1 channel (16-bit): Grayscale Best for grayscale images that will need major adjustment post-scan

16-bit, 3 channels (48-bit): RGB Best for continuous tone images that will need major adjustment post-

scan

“save the last (file) for me”

Saving and SharingRaw formats : straight from the camera or scanner; no post-processing or organizing the data; only usable in a very limited number of applications

TIFF : usually the largest digital files; supports many color profiles; different options for compression; cannot be displayed in a browser or email

JPEG2000 : smaller than TIFFS; supports multiple color profiles; different options for compression; doesn’t work in many browsers or email

JPEG : much smaller than TIFFs; viewable in web browsers; variable amounts of compression

GIF : very small files using an index color schemebut uncompressed; viewable in any browser.

PDF : great for sharing, especially text; web compatible; an open standard though not always a preservation one; not ideal for saving/reusing images

Saving and Sharing Compression:

Lossless ○ Compresses data but keeps the directions to reconstruct it.

Doesn’t compress as much as lossy compression.

Lossy○ Similar information is lumped together

Uncompressed image72 dpi8 bit RGB color83 KB

Compressed image72 dpi8 bit RGB color30 KB

Uncompressed image72 dpi8 bit RGB color83 KB

Compressed image72 dpi8 bit RGB color39 KB

Saving and Sharing

So, how do we save it?A copy to keep? (hi-res, original size, big file)

○ Tiff? JPEG2000?

A copy to print? (med- to hi-res, determined size, big to medium file)○ A 300 dpi JPEG? JPEG2000? A PDF?

A copy to view? (lo-res, determined size, small file)○ A 72 dpi JPEG? JPEG2000? A PDF?

A copy for comparison? (lo-res, small size, small file)○ A 100x100 pixel JPEG? A 100x100 pixel GIF? JPEG2000?

(baby we were) Born to Scan

Flatbed ScannersPros:•Reasonably good resolution and

color management•Can be adapted to fit both reflective and transparent materials

•Stands up to repeated use•Easy to use (usually)Cons:•Limited bed size•Lower resolution and quality than specialty scanners (some)

Slide or Film Scanners

Pros:•High resolution •Some models can handle both 35mm and medium slide formats

Cons:•Can only handle slide or film of specific sizes

•More expensive than flatbeds

Overhead ScannersPros: Can handle oversize materials, fragile

books, other odd formats or fragile materials

Usually come packages with software to do sophisticated image edits or batch processing

Some have robotic page turning elements

Cons: Difficult and time consuming to operate Expensive Low resolution

Drum and Roll Scanners

Pros: Can accommodate large formats Can capture in true CMYK colors Capable of very high resolutions

Cons: Materials must be sturdy yet flexible Can damage materials Only appropriate for reflective

materials

Scanning Software Differences

Different interfaces

have similar basic

features

Epson Interface

Color settings lists bit-depth but not “RGB”

Both resolution and print (document) size are changeable

Epson Scan in “Professional Mode”

Scanning Software Differences

Color settings lists document types but not “RGB”

Both resolution and print (document) size are changeable

Epson TWAIN

Scanning Software Differences

Things to look for in a scanner High “optical” resolution

Scanner specifications usually include an “optical” and “interpolated” resolution (and now we know interpolation is bad)

D-max or dynamic rangeThe lightest light and the darkest dark the scanner can

see. You want at least 2.0 (scale from 1.0 to 4.8) At least 24-bit “external” color

Another trick…”internal” or “hardware” is meaningless A transparency adapter

If you want to scan slides too

Take the manufacturer’s word with a grain of salt

Digital CamerasPros: Good for 3-dimensional objects Good resolution and zoom Can capture materials from multiple

angles Area-array (vs. line-array)

Cons: Quality can be dependent on

skill of photographer and external factors like lighting

Probably not as good for flat materials as a scanner

More ways to say the same thing “Megapixel”

Maximum number of pixels in an imageResolution will depend on what size you print

the imageWhen you open the image on your computer it

will default to 72 ppi

Optical Zoom vs. Digital Zoom“optical” zoom is actual zooming with the lens“digital” zooming is resampling! The quality

suffers…

Photo Editing Software Adobe Photoshop

Expensive ($699 to $999); professional quality; more tools than you will probably ever use; the ability to adjust everything manually

Adobe Photoshop ElementsMuch less expensive ($80); intuitive adobe design;

“auto” tools instead of manual ones Corel Paint Shop Pro

Much less expensive ($50); similar tool set; a little less intuitive than Photoshop; auto and manual tools

GIMPFree ($0!); similar tool set, but often different

terminology; auto and manual tools

Do we have time for a