Prepared by George Holt Digital Photography BITMAP GRAPHIC ESSENTIALS

Prepared by George Holt

Digital Photography

BITMAP GRAPHIC ESSENTIALS


Contents1.Describe a bitmap based graphic.

2.Use a graphics application software package to edit bitmap based graphic.

3.Create and print a bitmap based graphic.

4.Insert stored graphics into a current drawing and into a simple document.


Describe a bitmap based graphic.

• Identify the features of a bitmap based graphic.

• Describe how each graphic type is stored, ie file format

• Identify examples of bitmap based graphics.


Identify the features of a bitmap based graphic.

• Raster Graphics = Bitmap based graphics– Graphics made up of rows and columns of pixels.

• Pixels– The smallest unit of a raster graphic. A pixel

contains an individual colour.• Colour depth

– The number of possible colours that can be contained in a raster graphic. Eg 24 bit colour which gives 16.7 Million different colours.

• Resolution– A measure of the quality of the image in terms of

how many pixels it has. Eg 800x600 pixels or 300pixels per inch(ppi)

• Digital data– Data that can be expressed in terms of numbers. It

is both accurate and reproducible.


What are these file types?.jpg

.rtf

.PSD

.TIF .PDF

.BMP.GIF

.txt

.ppt

.xls.doc


Lets sort them out.?

.jpg.rtf

.PSD

.TIF

.PDF

.BMP

.GIF

.txt

.ppt

.xls.doc

Raster Graphics Documents


ResolutionImages can be

measured in 3 ways.• Megapixels eg 7.1MP• The number of pixels

Width x height.Eg 800x600=480,000pixels or 0.5MP

•The number of pixels per inch for printing on paper.Common resolutions include:•72 pixels per inch (ppi) for screen quality.

•150 pixels per inch (ppi) for Newspaper quality.

•300 pixels per inch (ppi) for photo quality.


Colour DepthThe number of possible colours that can be contained in a raster graphic.

Colour is stored in photographs by allocating storage space in the form of bits and bytes of data. Each pixel in a raster graphic is allocated a colour. Eg 24 bit colour gives 16.7 Million different colours.

24 bit colour means 24 bits or 3 bytes of data is allocated to each pixel in the image.


Colour DepthColour depth

No of Colours

Bits Bytes Notes

Black and White

2 colours2 to the power of 1 (because there is only 1 bit of data/pixel)

1bit 1/8 byte

Commonly used for scanned text documents

Greyscale 256 versions of grey 2 to the power of 8

8 bits

1 byte Greyscale is commonly referred to in photography as black and white but obviously the image contains more than just pure black and pure white.

24bit Colour

16.7Million colours 2 to the power of 24

24 bits

3 bytes Red – 1 byte – 256 variations

Green – 1 byte – 256 variations

Blue – 1 byte – 256 variations

256x256x256=16.7Million


Calculating File Sizes.File sizes for uncompressed raster graphics can be

calculated by multiplying the number of pixels by the number of bits per pixel.

Example1: Calculate the following file size as a bitmap.A greyscale image is 800 x 600 pixels800 x 600 = 480,000 pixelsa greyscale image uses 1 byte of data per pixel. 800 x 600 x 1 = 480,000 bytes divide by 1024 to get Kilobytes 800 x 600 x 1 /1024 = 469 Kb

Example2: Calculate the following file size as a bitmap.A 24bit colour image is 800 x 600 pixels800 x 600 = 480,000 pixelsa 24bit colour image uses 3 bytes of data per pixel. 800 x 600 x 3 = 1,440,000 bytes divide by 1024 to get Kilobytes 800 x 600 x 3 /1024 = 1406Kb


File Formats

Graphics are stored in files. Common File types include:• BMP an uncompressed raster graphic filetype. This is Microsoft's native

graphic file format.• JPG or JPEG a lossy compressed raster graphic. JPEG supports

millions of colours and allows for graphic compression. • GIF a lossless raster graphic that can only show 256 colours. Often

used for logos and animated graphics on web pages.• TIF a lossless compressed raster graphic. Can store layers and multiple

pages.• PSD This is Photoshop's native file format. If you have created a

graphic with a multitude of layers (especially type layers), and you want to save these layers for any changes that you intend to make in the future, then save the graphic in Photoshop format because it is the only format that allows you to save layers. For all other formats, you must first Flatten Layers (under the Layer menu) before you can save the graphic.

Look at the GRAPHIC FILE FORMAT OVERVIEW handout


RAW (*.raw)

• Professional Digital Cameras (High End)

• Uncompressed and unedited – excellent quality and detail

• Requires dedicated software to view images


TIFF (*.tif)

• Tagged image File Format

• A lossless compressed raster graphic

• Supports Layers and Multiple pages

• Commonly used for scanned text documents

• A common file type used in desktop publishing


JPEG (*.jpg)

• Joint Photographics Expert Group

• Most Common Image File used by Digital Cameras

• “Lossy” Compression – loses data on compression by merging colours.

• Image quality degrades as compression is increased

• 16.7 million colours


GIF (*.gif)

• Graphics Interchange Format

• Lossless compressed raster graphic

• Allows for a colour range of 2 to 256 Colours

• Not enough colour depth for photos but can have transparent sections

• Used for text, logos, animations and simple pictures.

• Commonly used for the Web although the PNG file type may partially replace it.


Photoshop Document (*.psd)

• Native Adobe Photoshop file format

• Allows complex image including layers and filter effects to be saved and edited at a later date

• Large file size


PDF (*.pdf)• Portable Document Format.• A file type developed by Adobe to standardise document

display.• Can contain images and text. Images are compressed

within PDF files as either GIF or JPG. Text is stored with its fonts embedded.

• Pages will be displayed exactly as they were formatted on the designers computer.

• Commonly used in web sites and can contain multiple pages, popup notes and hyperlinks.

• The Adobe Reader software is Free to download from the web.

• Documents can be password secured to stop changes or even printing.


Raster Graphic File Types Comparison

File Type Compression Web Layers Multiple Pages

Main Purpose

RAW No NO NO NO High grade images direct from camera.

TIFF Lossless (Large file sizes)

Yes Yes Yes Scanned text documents

JPG Lossy (Small file sizes)

Yes No No Photos on the Web or to email.

GIF Lossless (Small file sizes)

Yes No No Animations and logos on the web or logos and simple graphics in documents. Can have transparent sections. Limited up to 256 colours

PSD NO No Yes Used by Photoshop for works in progress

PDF Yes(Variable)

Yes No Yes Displaying documents exactly as they were designed containing text, fonts and graphics


Identify examples of bitmap based graphics.

• Check the properties of some common file types.

• Zoom into the image and see the pixels.

• Check the File properties from Windows Explorer. Right Click on the file and choose properties.


Editing raster graphics.

• Open a graphics applications software package and identify the basic information displayed on the screen, eg Photoshop or Paintshop.

• Identify the purpose of each of the basic graphics tools.• Use graphics tools to edit a graphic, eg resize, change

shape, colour.• Save a graphic, differentiating between 'save' and 'save

as'.• Store the graphic in a specified folder.• Exit the application without loss of data.


Model makeover

• Open the file for the model makeover.

• Identify the parts of the screen.• Select pixels• Change colours• Save changes to local C: drives.


Stonehenge Sunset

• Use layers to create the Stonehenge sunset from 3 images.

• The selection and magic wand tools can be used to delete unwanted parts of the layers.


Create and print a bitmap based graphic.

• Create a graphic using graphic tools to draw boxes, circles, text, lines etc.

• Use the features of the graphics software application to enhance the drawing, eg morphing, artistic appearance, colour balance, etc.

• Print the graphic using the functions of the graphics software application.

Do the Drawing with Photoshop Exercise.


Inserting stored graphics into documents.

• Retrieve created graphic from storage and insert into a current drawing.

• Insert a graphic into a simple created document.

• Edit the graphic from the document.

• Print the document.