1 Graphics Talk v1.1, Apr-2004Murray Niman G6JYB PC Graphics - From Megabytes To Modest Bytes By Murray Niman G6JYB

2 Graphics Talk v1.1, Apr-2004Murray Niman G6JYB The Problem SIZE MATTERS ! How is it I can download a web page such as BBC News which may have 40 Images in a few seconds? But my mates send me Megabyte photos which take ages to load and cost a fortune on the phone bill (or inkjet cartridges) OR I must have the latest 6-Megapixel camera - and I get the same problem

3 Graphics Talk v1.1, Apr-2004Murray Niman G6JYB Common Formats BMP - Bit Map (1, 16, 256,32K or 16M Colours, no compression) GIF - Graphics Interchange Format (Compuserve) (1, 16, 256) JPG/JPEG - Joint Photographic Experts Group (16m only) TIF - Tagged Image Format (Usually 16m) Also lots of others:- PNG - Portable Network Graphics, PCX, WMF, PBM, EPS etc etc Most of the ones we are concerned with are raw pixel data. Do not confuse with WMF, PDF, Flash, smart shapes, Wordart etc

4 Graphics Talk v1.1, Apr-2004Murray Niman G6JYB Other Formats Powerpoint - combines any Pictures with text and graphics Shockwave (SWF) & Flash - Vectored animation Movies:- AVI Microsoft Video (but can be compressed into WMV, DivX) MPG - Motion Picture Experts Group MOV - Apple Quicktime Movie GIF - Animated - Very inefficient but ok for web pages

5 Graphics Talk v1.1, Apr-2004Murray Niman G6JYB Colours A Pixel = A Picture Cell - one dot that is a colour Everything is binary: 1 bit = 0 or 1 = Black or White 16 colours = 4bits or half a byte One Byte 2^8 = 256 colours = a bit low for Colour photos Three Bytes = 24 bits, 2^24 = 16million colours (256 Red, Blue and Green) Note - a black/white photo is grey (RGB are all the same) Colour uses RGB so needs upto three bytes instead of one

6 Graphics Talk v1.1, Apr-2004Murray Niman G6JYB Pixels Pages and Sizes DPI - Dots per Inch (or pixels per inch ) An A4 page is ~12x8” dpiPixelsTotal Pixels 75900x600540, x800960, x12002,160, x16003,840, x24008,640, x480034,560, x ,240, x ,960,000 - and remember is often 3bytes per pixel for full colour

7 Graphics Talk v1.1, Apr-2004Murray Niman G6JYB Cameras, Scanners, Screens & Printers They are all different ! Screens are 75-90dpi Printers are Cameras / Scanners can zoom (Optical Zoom saves megapixels) You cannot get a 1:1 size from Scanner to Screen to Printer If you know its final use, choose the size in advance

8 Graphics Talk v1.1, Apr-2004Murray Niman G6JYB Size & Area This can give Big Gains... A picture that is half the size is a quarter of the area/no of pixels Crop unnecessary items around the borders Resizing the remainder down by 30 or 50% Line Graphics: If an image is a graph, circuit diagram, map etc it will only need between 2 and 256 colours - Using GIF is very economic and better quality than Jpeg High JPEG Compression doesn’t save much but can ruin photos

9 Graphics Talk v1.1, Apr-2004Murray Niman G6JYB Noise Need good quality originals: Clean high contrast images use far less space than noisy/busy ones (Lots of pixels can be tied up on grass blades, leaves etc) Raising contrast and decreasing/merging colours can save a lot Flooding a slightly noisy background with black or white etc can save a lot If it is almost grey, then make it a greyscale and reduce to 16 colours

10 Graphics Talk v1.1, Apr-2004Murray Niman G6JYB How Many Colours? Graphs/diagrams may only need 16 colours A photo may use 16million! (but rarely needs them all) A picture that is half the size is a quarter of the area/no of pixels Many pictures on the web are reduced to 256 or less So not only does size matter, colour count does too

11 Graphics Talk v1.1, Apr-2004Murray Niman G6JYB Example JPG: BMP: TIF: GIF(256): GIF(16): GIF(16) as JPG: 73647! 3200 Colours in Use in Original16 Colours in Use in GIF(16)

12 Graphics Talk v1.1, Apr-2004Murray Niman G6JYB Conclusions Formats Use the most appropriate for both quality and efficiency JPG for most Photos, GIF for Graphs, Circuit Diagrams etc Use a decent PhotoEditor like Paintshop Pro etc - not the freebies with scanners/cameras - they give you control over colours, pixels etc Sizes/Pixels, No of colours - Do you really need it all? Resize, crop. Keep a nice original, but use/send only reduced versions