What is more expensive on resorces?

[tonina]

Whenever you use the word "compressed" you have to think of quality loss. It's the same for video, images or audio. Larger image files use more resources of your pc since it has more information. Whenever you use a compressed image you are destoying it a bit, some compression methods make it almost unnoticeably. You can see it happening as you apply different compression percentages in photoshop, try yourself and you will see your image breaking down.
Your pc does NOT uncompress the image in order to display at your screen. The compression is done using algorithms to replace paterns at the moment you are saving your file, v.g. you may see almost no difference between an uncompressed image and a hi quality png, but for EDITING purpouses the most information you have, the better.
Uncompressed is more expensive in resources, compressed is for display purpouses only.

[aeres]

Whenever you use the word "compressed" you have to think of quality loss. It's the same for video, images or audio. Larger image files use more resources of your pc since it has more information. Whenever you use a compressed image you are destoying it a bit, some compression methods make it almost unnoticeably. You can see it happening as you apply different compression percentages in photoshop, try yourself and you will see your image breaking down.
Your pc does NOT uncompress the image in order to display at your screen. The compression is done using algorithms to replace paterns at the moment you are saving your file, v.g. you may see almost no difference between an uncompressed image and a hi quality png, but for EDITING purpouses the most information you have, the better.
Uncompressed is more expensive in resources, compressed is for display purpouses only.

You are talking about lossy compression. There are lossless compression algorithms such as RLE (http://en.wikipedia.org/wiki/Run-length_encoding) for .TGA files and LZW (http://en.wikipedia.org/wiki/LZW) for .TIF files. Lossy compression throws away data that the compressor deems redundant while lossless compression retains all the data. For example, a 16kb .TGA on your harddisk may take up 1.6MB of memory when you load it in Photoshop or whatnot, with no quality loss.

a .TGA file that takes up 1.6MB of system memory may only occupy 16kb in your harddisk after compression, with no quality loss. Lossless compressed file incurs processing overhead compared to uncompressed files because your computer have to put them back together.

[beaker]

I've been wondering, what is more expensive on computer resorces, an uncompressed file or a compressed file.

This may sound like a dumb question but, everytime a computer displays, say, a png image, does it have to uncompress it to normal 1.4meg (or whatever an uncompressed file size it) or just print it on screen?

Does anyone follow me??It really depends on the compression you are using. Not all compression schemes are created equal. PNG for example, I was using it quite extensively because it creates some of the smallest files for a lossless compression. The trouble I found is that it is very slow to read and write. So now I only use it to archive material, not for actual day to day work.

At work we use all Tiff with LZW compression. It is very fast to compress/uncompress and is compatible with all the appications we use. We are a big Discreet house, so thats why tiff is the preference.

Personally, whenever I am setting up a pipeline, I now use OpenEXR files with Piz compression. It provides the smallest file format that is still fast to read/write and supports scanline/bucket read and writing(means the application can read just the part of the image it needs, not the whole image).

[gmask]

As far as I know most display devices do have to decompress and image to display it. But this has become trivial in terms of displaying single video res stills or even moving video.

However if you are talking about a workgroup environment and you have thousands of images being loaded over a network then raw bandwidth will become an issue. In which case even though a compressed image will need to be decompressed to be displayed or used in software you still have to transfer the image over the network and smaller files means less bandwidth.

Consider the internet.... it would be unreasonable to download everything uncompressed.
In that case your most precious resource is bandwidth.

Using non lossy compression like RLE and LZW can have huge savings depending on images especially ones that are elements that only fill part of the frame on a black background.

The typical user must also consider file storage as a valuable resource. If you can save space with lossless compression then you should. Today's computers can handle decompressing them in realtime.

In terms of games etc I have to assume that loading compressed images of CD is not only a better use of space on the CD but also allows faster loading times because it is less data to move around.. so even though this file might balloon into memory once it's decompressed there have been great savings in resources in getting it into memory.

So in short... there is no reason to not use lossless compression if it's available. It will save space and does not reduce the quality of the image. In cases where bandwidth is limited then file size must be decreased at the cost of a degraded image to an acceptable degree.

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