As said, digital optical information is stored in digital image files. This happens in various ways, and as a result there are various image file formats. We will see here the most important ones, because later we will want to save our work -- in what file format will this be done?
PSD and PNG are good for DTP and prepress applications, and in multimedia when we want transparency at the file level. They are very useful and widely supported. Their difference lies in the fact that a PSD file can have layers but PNG not.
For the same reason, a JPG file may not be saved twice. From a lossless file i may create a JPG anytime for a web page or an email. If this file, which has been made as lossy, is opened in an image editing application and saved again as a JPG, new loss is summed up, so we have a further loss of quality. If i want to have a JPG with precicely controlled compression, i should better open the original lossless file and have a JPG from that one, so the loss happens only once.
If we need to save transparency, we prefer PNG, since JPG does not support transparency. So we have color depth of 24bit, a lossless and selectable compression, and it is used mainly on the internet.
XCF
This is the GIMP file format. GIMP will be the basic software with which we will do our digital image processing, and this software has an inherent file format to save our work - the XCF file format.- It supports layers - of course we will discuss layers in detail later in the school.
- It supports a lossless compression, which gives us a smaller file size but still without loss in optical quality, and about 30% better compared to PSD (which is the inherent file format of Photoshop).
- Its relative disadvantage is that some other programs do not open it, however GIMP both opens and saves PSD.
- It supports color depth to 24bit.
- It supports transparency at the layer level.
- Together with the layers saved, we can save valuable information with our work like channels, selections, and such, as we will see.
PSD
The file format of the known Photoshop is widely supported in many applications that import image data. Color depth is 24bit. It supports transparency, layers, and other important information. GIMP both opens and saves PSD, apart from some minor issues.PNG
Another well known format, widely supported in the web and multimedia applications. It features transparency to 24bit, and offers a compression algorithm which is theoretically lossless and selectable.PSD and PNG are good for DTP and prepress applications, and in multimedia when we want transparency at the file level. They are very useful and widely supported. Their difference lies in the fact that a PSD file can have layers but PNG not.
JPG
A well known format, appropriate for photos and photorealistic images. It supports 24bit color depth. It supports compression, which is selectable - this effectively being its strong point. Its only disadvantage is that it is lossy. The degree of loss is related with the compression selected. The compression algorithm allows for a huge range of compression, and of course greater compression results in lower quality. In the web we are concerned about small file sizes, and JPG is widely used because of that by offering a selectable compromise between compression and file size. Due to the compression and the consequent loss, it should not be used for archiving. For our photo archive we should prefer other file formats that are lossless.For the same reason, a JPG file may not be saved twice. From a lossless file i may create a JPG anytime for a web page or an email. If this file, which has been made as lossy, is opened in an image editing application and saved again as a JPG, new loss is summed up, so we have a further loss of quality. If i want to have a JPG with precicely controlled compression, i should better open the original lossless file and have a JPG from that one, so the loss happens only once.
If we need to save transparency, we prefer PNG, since JPG does not support transparency. So we have color depth of 24bit, a lossless and selectable compression, and it is used mainly on the internet.
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