Why would I ever want to rasterise text? What is the purpose of this operation?
There are many reasons why you would want to rasterize text. I agree that in general one does not want to do it if it can be avoided. Reasons for rasterization:
You dont trust the end users application to do it correctly or you are having some issues with your own/a known rasterization engine. In these cases you can gain benefits. This can be a valid strategy when sending things to print, or when dealing with computer presentable content/video.
You need to ensure uniform reproduction on different operating systems. Different systems deal with fonts differently and this may cause some problems on embedded devices like phones or Windows vs osX.
Target device is unable to do the rasterization.
You want to share a preview of a document and not share your assets. Rasterization nicely sidesteps the issue.
Enabling basic users to use your work, such as embedding it in a Word document. While there are better options in many cases the average user is not always able to use this approach. Using vectors in word is sometimes a insurmountable problem.
You want to apply some effect to the font. Effects are in general easier to build in a discrete setting and many effects may be impossible to do in full form.
tl;dr: Type that isn't rasterised won't stay in shape on other machines. That's a bad thing for sharing and printing the
.psd file. You may also want to use pixel editing on the letter shapes.
If you don't share the
.psd file and don't intend to use pixel-only effects on the letter shapes, there is no good reason to rasterise. As sharing a
.psd and pixel-only editing tools are rare, rasterisation is usually unnecessary.
Type that is not rasterised depends on a font file for its appearance. Usually, this font file is present on the system you make the type on. So far, no problem, and no need to rasterise the type. It only reduces editability, right?
The fun starts when you want to send the file you're working in to another machine. You might want to do that to share your work with someone else, but also to get the file printed.
If you open a, say, Photoshop file with unrasterised type in it on another machine and the font you gave it is not present on that machine, the text will 'break'. It will default to a standard font like Verdana or—shiver—Times New Roman.
It's not always convenient to include a font file with any work you send. Because it will likely cause licensing problems if you used a non-free font. Also because it requires work from the receiver: they have to install your font to see your file properly. Not convenient.
A crucial scenario happens when you send a
.psd file to a printer (not the desktop kind, the company kind). When the printer receives your file, they need the information in the font file to be able to output the text in your file properly. If they don't have the font file, they will replace with Courier if you are lucky. If you rasterise your type, you embed that information into the
.psd, allowing them to print without issues.
Do note that you seldom share
.psd files. Delivery to a printer should be in
.jpg or maybe
Another reason could be that you'd want to edit the appearance of the type in ways that are not possible when it's still a text layer. Imagine you'd want to use the smudge tool on a part of a letter, you will have to convert your type into pixels first, as smudge doesn't work on vector or text layers.
Current versions of Photoshop have almost no editing tools left that cannot be applied to a text layer or a smart object. Frankly, I had to look hard to find the smudge example.
Rasterisation of your type is a so-called destructive operation. It disables you from editing the type as type later. Usually, this is a bad idea. You want your files to be as editable as possible.
If possible you should always retain the vector information in your type, ideally by leaving your type as an editable text layer, converting it to a smart object or converting it to a shape layer.
However, certain filters and tools in Photoshop (depending on which version of Photoshop you are using) can only be used on raster layers.
Some commands and tools—such as filter effects and painting tools—are not available for type layers. You must rasterize the type before applying the command or using the tool.
Note—I am only talking about type in your working Photoshop document, not exporting to a raster format, which is a completely different issue.
To some extent its what others said, however, a big point was left out -- Smart Objects.
Smart Objects were introduced in Adobe Photoshop CS2. Prior to this in order to use a number of Filters and techniques would require the type (and any vector really) be converted to Raster. This is for stuff like Glowing Edges, Texturizer, etc.
Then Before version 7 (technically 6, but nobody used 6) there were no Layer Styles either. Back in the early days then if you wanted to apply say a text glow or a drop shadow you had to raster the text and use a blur technique to do so.
Now with the usage of Smart Objects there is really very little reason to Rasterize text. It's more of a legacy feature they never removed. Smudge is just about the only tool that can only be used on rasterized type.
To better explain - let's say you want to erase some of your text, now this can be done with a mask. Want to Liquify the text? This can be done after converting to Smart Object. Want to Gradient it? Use a Gradient Adjustment Layer. Want to splice it up into pieces? Use multiple copies of a Smart Object. Literally, the only thing someone has mentioned to me that I've not found a way to do without rasterizing the type is the Smudge Tool. Anything else has non-destructive alternatives. And you should strive as much as possible to be non-destructive in your work.
There might be some other very minor instances if you're say creating your own filter or scripting. Beyond that, not really.
Update: This is for a non-destructive workflow which is generally the best method. However, if your task would involve hundreds of smart objects vs a single pixel layer it might not be. You'd have to decide for yourself though and hope you get it right. Redoing either could be a potential nightmare.
If anyone thinks of a pixel operation they think requires them to rasterize the text let me know and I'll either find a non-destructive alternative or update this answer.
The purpose of rasterizing text, effects, or anything for that matter, is to have a flat, non-editable, non-variable file format, and a fixed interaction with its background, whenever the output needs it. (1)
In commercial printing, all work is at some point rasterized. If you send a vector file, for example your flyer for print, the RIP (Raster Image Processor) rasterizes it.
It rasterizes it accordingly to the laser used to generate the plates, and it converts the image into a pure black and white information. It fires a tiny dot of laser or not. The same principle I mentioned applies. It needs a very precise instruction.
Rasterizing it is one simple thing. Converting the instructions of a vector file (note the word "instructions") into a fixed map of information is called a bit-map.
(1) I am adding this appendix on why YOU, as a designer, ever want to rasterise text. Here are some examples:
Is to be flat
You need to send a banner for print, and the provider needs a JPG file.
You need a nice banner for a website.
You are sending a mockup to a client.
You do not need or want to release an editable file.
Non-variable file format
- You are sending an ad to an overseas provider and you will never see a print proof or soft proof.
A fixed interaction with its background
- It has some effects, transparencies, blending modes, etc.
Whenever the output needs it.
- The required deliverable file format does not support that, for example some flavors of a PDF.