Images can be basically be specified in two main areas, pixels and colours. The pixels is the images size (more pixels the bigger the image) and colour which controls how the image will look. There are of course other ways the image can be changed. There can be some external influences like monitors, for example a monitor which displays 256 colours will display all images in 256 colours at the most, no matter what format the image is in. You can also change the resolution which involves increasing or decreasing the amount of pixels viewable or the DPI dots per inch or PPI pixels per inch.
Bitmap graphics record all the pixels in that image to save and recreate the image later. This as you can imagine requires more storage space.
Vector graphics uses a mathematical description to save and recreate the shape so instead of saving the image itself it saves the image as instructions which it then uses to create the image when required. This is a lot more space efficient but also a lot more complex and can’t always be done with some complex images.
Colour models are different methods the computer can use for coding the colour in an image. They all have different variables that are combined to create the desired effect. RGB or red green blue is the most common but there is also CMYK or cyan magenta yellow and black which most printers use and HSV or hue saturation brightness.
Colours can have different depths. The greater the depth the more colours the image can use. 24 bit would refer to millions of colours while 8 bit would be 256 colours. You have to find the contrast between the image size which increases with the more bits you have and how many colours you really need.
The colour format can be in two forms, indexed and direct. Indexed colour involves bits which equals 256 colours. The 256 colours are chosen from the most commonly used colours contained within a CLUT or a colour lookup table. Direct colour can be 24 bit, millions of colours and doesn’t use a lookup table.
Images can be edited using a variety of methods. The most common methods are selections, layers, masks and pixel point processing. Selections involve selecting part of the image to edit while leaving the rest of the image untouched. Layers add another aspect on the top of an image. Multiple layers can be added to the image. Masks can be used with layers to create special effects such as a gradient. Pixel point process involves editing a curtain pixel. Different effects include brightness adjustments, colour adjustments, filters, effects, blurring, sharpening, distorting and image.
The GIF file format is mainly used for pictures that do not require a lot of colours. GIF has features such as lossless compression and transparency.
JPEG is best used for complex images such as photos. Unlike GIFs, JPGs can contain more than 256 colours.
PNG was created to replace JPG due to a copyright disagreement which meant people would have to play to use the file format. It was created to have the benefits of both the GIF and the JPG file format. The confict was however resolved and PNG never really took off.
Other file formats also use images like animations which contain many still images played at a fast rate of speed to create the impression that it is moving.
It was really interesting to find out about all the different file formats and the specifications of the image. I'm sure it will be very helpful in the future for any time I need to make an image.
For my independent reading this week I researched two articles on image formats shown below.
In today’s tutorial we learnt about creating buttons in Photoshop. To create the image we first specified the amount of pixels for the height and the width specified and the background colour. We experimented applying a block colour and a transparency. We then created different layers for both the text and the background gradient. When then applied different effects to these layers to create the completed image. Below are the buttons I created using Photoshop. It was a really interesting tutorial, I kind of feel we know the basics right now which is nice considering by ability in Photoshop was very mixed when I first started. Below are the text and the buttons I made in the tutorial.
- Image formats overview
Last accessed 28/01/08
- How stuff works – image formats
http://computer.howstuffworks.com/question408.htm
Last accessed 28/01/08
Button:
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