Information Technology

Understanding Digital Raster Images & Photos on Computer

Raster terminology is used for photos/pictures on your computer. All images/photos/pictures that you get from any digital device(camera, scanner etc) are raster images.

The terms image, photo, picture, raster are all synonymous on digital media.

A raster image on a computer can be stored in variety of formats like Jpg, Gif etc. Every format has some or other advantages/disadvantages like compression, bits per pixels, transparency etc.

A raster is a rectangular shape in which pixels are laid out horizontally as well as vertically. The horizontal array of pixels is called a row while the vertical array is called column.

A raster is always rectangle in shape.

A raster can store multiple colors or bands or channels(in Photoshop).

Although there are many color models like HSB, CMYK the raster images on computer are in RGB(Red, Green, Blue). Even your monitor/TV's are laid out in raster with each LED a pixel.

Images are composed of pixels and each pixel is composed of three basic colors: Red, Green and Blue(there are other models like HSB/CMYK etc). Each pixel is of 4 bytes and each byte can contain value from 0 to 255. So for three colors(RBG) we've 3 bytes and top most byte is left unused. That means 256 values of hues in each bytes. So three bytes will give 256*256*256 = around 16 million colors!

A color raster image consists of three independent channels/bands/colors/planes(called RGB):

A color raster image consists of three independent channels/bands/colors/planes

To make your life simple assume a color picture is of rectangular shape and consisting of three planes or channels(in Photoshop):

  • plane-1(Red)
  • plane-2(Green)
  • plane-3(Blue)

Also each plane is absolutely independent of each other. If you view picture of each color or plane or channel it'll be black & while in gray consisting of gray color pixels lined up horizontally and vertically.

A raster image containing pixels organized in rectangular fashion:

A raster image containing pixels organized in rectangular fashion

For sake of simplicity assume we've only a black/white image containing single channel unless specified otherwise.

As you see above, pixels are organized in rows and column and there are 11 pixels in horizontal row and 11 vertically. So counting all we've got 11 * 11 = 121 pixels in total. Now each pixel usually occupies 1 byte( 8 bits). 1 byte can contain anything from 0 to 255. In short a pixel's value can have 256 values. In other words they are organized in x-axis or y-axis with origin (0,0) at top left cornet. Remember those numbers in red are the pixel positions from origin counting from 1.

So this was for single plane/channel or band. Now for a color pixel we have three basic colors. So each color will have another rectangular array of pixels. So total of three rectangular grid.

Yes these three rectangular grids are stored separately in different ways in different formats. But how do we see color image then? Each pixel on your computer has 3 LED's - R,G,B and when they each light up using values from your three rectangular grids in different intensities we see a color pixel.

For CRT or old style monitors there will be three electronic guns one for each R, G and B. Each gun is fed value from your grid and lights up depending on the value of the pixel of that particular color(R/G/B). So on screen when three colors mix up at a point - they light up in color!

What you can expect in your iPad app on iOS 5 ?

iOS 5 will hit the stores this fall. Do you already have an app idea for iPad app on iOS 5? Here are a few iOS 5 features that you can utilize in your app for a great user experience.

iOS 5 is expected to be made available by fall this year. The tech pundits have already labeled it as an operating system that is years ahead of its time. It is expected to take the OS experience to an all new level. There is a lot of patter around the new features added in iOS 5. The official website of Apple states they have added 200+ new features to iOS 5. Custom news stand, centralized notification, un-tethered syncing, Tweeter integrated with the OS are some of the awe-inspiring features of iOS 5.

iOS 5 will be compatible with a selected versions of iPhone and iPod touch. However, for Apple Inc's tablet versions, the soon-to-be launched operating system will work equally well on iPad 1 and iPad 2. For those who are looking forward to developing iPad app on iOS 5, here are some of the features that can enhance your users' overall app experience.

A smarter camera option for the iOS 5 - When in the camera app, the volume button doubles up as a shutter release key. You can add the grid lines for a composed picture. In-device editing tools make it an intelligent camera. The camera app has some new features and some simply enhanced for a better user experience. Once you fix the frame, you can lock it with a swipe. The app optimizes the snap according to the lighting conditions. You can pinch to zoom in/out while taking the snap. Red eye reduction and easy cropping make editing quick and almost effortless.

Do you already have lots of app idea for iPad app on iOS 5? Consider utilizing the camera in your app. This will go a long way in making your app a success in the app store.

Maps get a face lift on the iOS 5 - Clever and quick to browse. Apple has completely revamped the way Google maps are used. iOS 5 simply takes the Google map data and presents it differently. It suggests you multiple routes with a three-dimensional tube line and gives you waking directions. This is definitely and whole new way of using the same old Google map. If your app concept involves using the Google map, kudos!
The iOS 5 is portrayed as a platform that is expected to propel building up of thousands of novel apps which would be used for varied purposes such as business, entertainment, spots, multimedia, medicine and much more.

OpenXcell Technolabs is a prominent iPad app development company. It has a team of expert iOS programmers that can develop custom iPad app on iOS 5 as well. To know more about the company visit, http://www.openxcell.com. The original article appears here.

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