HNC Digital Imaging Bitmap images Vector images Resolution

HNC Digital Imaging • • • Bitmap images Vector images Resolution File formats Colour modes File management and naming Appropriate software Storage Input and output devices

Bitmap Images • Digital photographic images are bitmaps • Definition: • Bitmap, is a data file or structure representing a generally rectangular grid of pixels, or points of colour, on a computer monitor, paper, or other display device. • Source: http: //en. wikipedia. Org/wiki/bitmap

Binary data • In computer terms, a "bit" (binary digit) is the smallest piece of information and has a value of either "0" or "1" which actually corresponds to one of the millions of "switches" inside the computer being "ON" or "OFF • In a 1 bit image we can assign the binary value "0" to black and "1" to white.

Bits and Levels • A 2 bit image can have 22= 4 tones: 00 (black), 01 (gray), 10 (gray), and 11 (white). • An 8 bit image can have 28 = 256 tones ranging from 0000 (0) to 1111 (255). • These 256 tones correspond to the Levels used in the histograms palette and help you analyse the image’s exposure

Bits and photographs • Images are often referred to as 24 bit because they can store up to 8 bits in each of the 3 colour channels and therefore allow for 256 x 256 = 16. 7 million colours. • JPEGs, Tiffs, PSD, Raw, PDF file formats all work on this principle and are all bitmap files

Back to pixels, bits and bytes • Each pixel records 8 bits of data, resulting in 256 levels of tone. • Each pixel has 3 colour channels in red, green and blue. • Therefore each pixel contains 24 bits of data.

Memory hierarchy • • • A bit = 2 values of 1 or 0 8 bits = 1 byte = 256 possible values 1024 bytes = I kilobyte (KB) 1024 kilobytes = 1 megabyte (MB) 1024 megabytes = 1 gigabyte (GB) It is vital that you are familiar with these terms. • There are implications for image quality and storage of your work.

Pixels and document size • • If each pixel contains 24 bits of data. Then each pixel contains 3 bytes So 6 million pixels = 3 x 6 million bytes Which is why a 6 mp camera produces an 18 MB file.

File and document sizes • There are several ways of expressing a digital image’s “size”: Pixel dimensions output resolution output dimensions bit depth file size (open) file size (closed) It is essential to be familiar with all of these.

Formats and compression • A file may have a completely different size when closed or open. • This is due to the compression of some file formats. • Bitmap formats that we use are: JPEG, TIFF, PSD, PDF and RAW

File Formats • JPEGS: High compression options, “lossy”, memory efficient, (Jpeg is a compression algorithm used by other file formats too) • TIFF: Lossless compression, supports layers, supports more than 8 -bit colour depth, cross platform • PSD: Photoshop format, supports layers and high bit depth, lossless • PDF: lossless, cross platform compatability • RAW: Unprocessed data file produced by top end SLR cameras. High bit depth and optimum quality images. The professional choice.

File management • • File naming eg env-proj 1. tif Embed caption and credit data (Exif files) Back-up your work Edit and delete Find your files within 3 -4 mouse-clicks Use file browse or Bridge for initial edits Present work clearly and efficiently Think: workflow and efficiency

Workflow • • • Step 1 -load images from camera Step 2 -rename all files Step 3 -1 st edit, in browser, or bridge Step 4 -store in named folders Step 5 – 2 nd edit and image correction in Photoshop • Step 6 – store caption and credit data • Step 7 – back up work, and deliver • Tip: consider automating common actions

Colour management • Colour rendition is both subjective and device dependent • Each link in the chain can introduce variables eg subject lighting, camera settings, image processor, monitor display, inkjet or photographic printing • Aim of colour management is to reduce device dependency and limit the variables

1 st steps in colour management • Ensure that you are working in RGB colour mode • Embed an ICC colour profile for each image • Without a colour profile, colour representation can be almost arbitrary • Calibrate the computer monitor • Work in neutral and consistent conditions

Colour spaces No form of imaging can match the human eye’s ability to render colour. There are many ways that we attempt to define or map colour. RGB treats each value as a co-ordinate on an axis, giving a 3 dimensional colour space. Another method is to use hue, saturation and brightness as the values. HSV or HSB mapping.

Vector graphics http: //en. wikipedia. org/wiki/Vector_graphics • Vector graphics use geometrical primitives such as points, lines, curves, and polygons, which are all based upon mathematical equations to represent images in computer graphics.

Vectors vs Bitmaps • Vectors are resolution independent - they don’t use pixels • Therefore they can be scaled up and down with no loss of quality • But they cannot reproduce the tonal range and colour of photography • They can reproduce line drawings and solid colour • Vector files are much smaller than bitmaps

Vetor Uses Vector graphics produced in Illustrator have an AI suffix. Photoshop selections can be saved as EPS files. • Vectors are suitable for graphics such as logos and scaleable display text • Adoe Illustrator is a vector based programme, and Adobe Photoshop can convert ‘selections’ into vector graphics