Bitmap images

Bitmap images

Resizing bitmaps

Vector images

Why are there so manyimage file formats?

Resolution andScanning

“Bits” and .bmp files

Photo editors

JPG file formats

GIF file formats

Animated andtransparent .gif’s

Getting images fromthe web

What are the differentimage file formats?

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cadia University

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Created by Sheila M

acLeod Potter, w

orking for the AIT

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cadia University

Bitmap imagesBitmap images

‘Bitmap’ refers to digital images which are composed of dots or pixels

In a bitmap image, the image file has to define the exact colour of every pixel in the image

This bitmap image has been stretched so that the pixels which compose it are clearly visible.

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Resizing bitmap imagesResizing bitmap images The more pixels which compose an image, the larger its file

size. The number of pixels in an image can be increased in two

ways by making the image larger in a photo editor.

Tell me more about photo editors! by increasing the image resolution

One confusing thing about the term bitmap is that there is a windows image format (.bmp) which is also referred to as a ‘bitmap’. To avoid this confusion, some people use the term raster when referring to images composed of pixels.

Bitmap file formats include .jpg, .gif, .bmp, .tif, .wpg, .psd, etc.

Why are there so many image formats?Why does the computer ask me about number of bits when I go to save my image as a bmp?

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Vector imagesVector imagesVector images are not made up of dots. Instead, they are

composed of shapes and lines. Vector shapes are defined by the direction of the line which

runs around their perimeter.Vectors have several useful qualities: they are infinitely scaleable they usually have smaller file sizes than bitmaps they are crisp and clear when printed Note that: vectors on screen appear pixilated because the

computer screen is composed of pixels!

bitmapvector

To see how thisvector graphicretains its smoothoutline, hit Escand then zoom into %400.To resume show,click F5.

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Why are there so many image file formats?Why are there so many image file formats?

There are almost as many image file formats as there are programs that work with images.

There is a great deal of competition in the graphics world among companies trying to create the best artist’s tool.

Companies like Adobe and Corel, for example, each have software packages for working with images, which do many of the same things, yet they each (Adobe Photoshop and Corel PhotoPaint) have their own image file format (.psd and .cpt).

At one time, different image file formats could only be opened by the software in which each was created, however, today, most common packages will let you open other company’s formats.

One practical reason for different formats is that each saves a slightly different set of information with the file. For example, .jpg is a compressed format (small files), in which the minimum information is saved. By comparison, .tif is uncompressed and can save more file information.

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Image File FormatsImage File Formats.jpg and .gif are the best formats to use for presentations and for the

web because they are both compressed in file size. Uncompressed formats such as .tif are best for print, however, there are many other formats which you may come across:Other Bitmap formats:

.tif : uncompressed image format which is good for use in printed projects like pamphlets and posters.

.wpg: format used by Corel Presentations .bmp: windows preferred image format (your wallpaper

is a .bmp) .psd: layered file format used in Adobe Photoshop .cpt: layered file format used in Corel Photopaint

Vector formats: .cdr: CorelDraw format. MS PowerPoint often has

difficulty reading this format. .wmf: “windows metafile” format. this format is widely

accepted by programs which use vectors, including MS PowerPoint, and Word.

.fla: animated vector file created in Macromedia Flash

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Photo EditorsPhoto Editors although, images can be stretched, or cropped within

PowerPoint, this does not alter their file size. in order to crop an image so that parts are eliminated from

the image file itself (and the file becomes smaller), a photo editor such as MS Paint, Corel Photopaint, or Adobe Photoshop must be used.similarly, when you stretch or shrink an image in PowerPoint, the file size is not effected.

Image file size must be changed in a photo editor by changing the resolution, cropping, or resaving in a compressed format such as jpg or gif

“handles” appear all around imagesin PowerPoint, and can be ‘clicked and dragged’ to enlarge or shrink the image, but this does NOT change the image’s file size or resolution. HOMEHOME

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cadia University

JPG file formatJPG file formatJPEG is a popular format for two reasons:

It keeps photographic images clear It lets you adjust the amount of compression

JPG format should be used for photographs which contain a lot of detail and thousands of colours

JPG compression does change the way an image looks

uncompressed (tif)file size = 152Kb

slightly compressed (jpg)file size = 31Kb

highly compressed (jpg)file size = 10Kb

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GIF file formatGIF file format

GIF format should be used for diagrams or drawings which contain few colours

If the image contains 256 colours or less, gif compression does not change the way it looks

In a .gif image, the number of colours is reduced to 256 and then "runs" of same-colour pixels are encoded in a colour + number of pixels format. This makes a .gif file great for storing drawings that have lots of same-colour pixels. gif images are common on the web.

What’s an animated gif or a transparent gif?

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Why does it ask me about the # of bits when I save my .bmp files?Why does it ask me about the # of bits when I save my .bmp files? The more colours in an image, the more bits are

required to represent it digitally. The best-looking images contain 16 million colours

(this is known as RGB [Red Green Blue] mode) Imagine a bitmap in RGB that is 400 by 400 pixels.

Saving this image requires 24 bits per pixel for 160,000 pixels, or 480,000 bytes.

480,000 bytes = 480 Kb which would take considerable time to download from the web

For the sake of comparison, an RGB .jpg containing the same number of pixels (400X400) might be as small as 5Kb.

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Animated & Transparent gif.sAnimated & Transparent gif.s

What’s an animated gif?Animated gifs are also ‘.gif’ files, but they are

actually composed of multiple gif images which cycle to give an animated effect. Animated gifs files are as big as the sum of the gif images which compose the animation.

Why does this gif file look differently on my machine than it did on the web?

Many photo editors will allow you to assign a “transparent colour” within a gif image. That’s why, when you download gif’s from the web, sometimes an ugly background colour appears when you open the gif in another program. The ‘transparent’ colour only looks transparent on the web!

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Copying and Downloading images from the webCopying and Downloading images from the web

There are two ways to get an image off the web.1. copy and paste2. save it

Copy and Paste copy the whole screen (PrtSc) OR copy the active screen (Alt+PrtSc) AND paste (Ctrl+V) directly into your document

Save Right Click, Save As you can’t choose a file type, but you can give the

file a new name

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Resolution and ScanningResolution and ScanningResolution: Image resolution is expressed in dots (or pixels)

per inch (dpi).When scanning an image, the resolution you choose depends on the way that you intend to use the image, or how it will be displayed.

Suggested Minimum Resolutions: for use on the web and in presentations: 72 dpi for print: 150-300 dpi

If you are scanning an image for use on the web or in a presentation, you may wish to “blow-up” the image by scanning it at a resolution higher than 72 dpi. Computer screens display at 72 dpi, therefore, small images that are scanned at higher resolution will be displayed larger on the computer screen.

image size = 1 X 1; resolution = 100dpi

1 inch

1 inch

Image