Interlaced BitmapInterlaced bitmaps are bitmaps where the rows of pixels ("scanlines") are stored out of sequence.
For example, the odd numbered scanlines might be stored first, and even numbered scanlines might be stored later.
Some Bitmap File Formats allow interlacing, but others do not. When a bitmap file is interlaced, it potentially allows the bitmap to be displayed progressively as it is received (for example, as it is received over the Internet).
Let's look at an example...
Imagine a file format:
Next, we would receive the 2nd, 6th, 10th, 14th, etc. scanlines. We now have (combining this with the data already received), half of the image data. There are still many gaps, but we can guess how to fill these gaps by simply duplicating the 2nd scanline into the 3rd and 4th, the 6th scanline into the 7th and 8th, and so on. As you can see the image begins to look more recognisable:
Now, we would receive the 3rd, 7th, 11th, 15th, etc. scanlines. We now have (combining this with the data already received in the two previous stages), three quarters of the image data. There are still some gaps, but we can guess how to fill these gaps by simply duplicating the 3rd scanline into the 4th, the 7th scanline into the 8th, and so on. Now the image is even more recognisable:
Finally, we receive the remaining scanlines, and thus we complete our image.
The important point to note, is that we were able to begin displaying an approximation of the image, even when we had received only a fraction of the total image data. Furthermore, as we received more and more image data, we were able to progressively display the picture in stages until the final image was displayed.
This can be a very useful feature when transmitting images over the Internet (of course, it requires a Bitmap File Format that supports interlacing, and browser software capable of this type of progressive display), as it allows users to begin to see images even before they have completely downloaded, and increases the perceived speed of web pages' display.
An actual example of a format that supports interlacing is the GIF file format. GIF interlaces based on every 8th scanline, which allows images to start to be displayed after only one eighth of their data has been received.
Disclosure: Our company's websites' content (including this website's content) includes advertisements for our own company's websites, products, and services, and for other organization's websites, products, and services. In the case of links to other organization's websites, our company may receive a payment, (1) if you purchase products or services, or (2) if you sign-up for third party offers, after following links from this website. Unless specifically otherwise stated, information about other organization's products and services, is based on information provided by that organization, the product/service vendor, and/or publicly available information - and should not be taken to mean that we have used the product/service in question. Additionally, our company's websites contain some adverts which we are paid to display, but whose content is not selected by us, such as Google AdSense ads. For more detailed information, please see Advertising/Endorsements Disclosures
Copyright © 2005-2014, Answers 2000 Limited
In Association With Amazon.com
Answers 2000 Limited is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.
In Association With Amazon.co.uk
Answers 2000 Limited is a participant in the Amazon EU Associates Programme, an affiliate advertising programme designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.co.uk.
CERTAIN CONTENT THAT APPEARS ON THIS SITE COMES FROM AMAZON SERVICES LLC. THIS CONTENT IS PROVIDED 'AS IS' AND IS SUBJECT TO CHANGE OR REMOVAL AT ANY TIME.
CERTAIN CONTENT THAT APPEARS ON THIS SITE,COMES FROM AMAZON EU S.à r.l. THIS CONTENT IS PROVIDED 'AS IS' AND IS SUBJECT TO CHANGE OR REMOVAL AT ANY TIME.
All trademarks are property of their respective owners.
All third party content and adverts are copyright of their respective owners.
Some graphics on our web sites are Copyright (C) 1997-2000 Hemera Technologies Inc., and used under license. All such pictures are provided for viewing purposes only and are not to be saved or downloaded. All such pictures of recognizable individuals are models and used for illustrative purposes only, and not meant to imply any association or endorsement of said individual with any product or service.