What is the difference between: image / x-citrix-pjpeg and image / pjpeg

Question

Some files are downloaded with a message like MIME:

image/x-citrix-pjpeg 

They are valid jpeg files, and I accept them as such.

I was wondering: why is the MIME type different?
Is there a difference in format? or was this mimetic invented by some kind of light bulb in citrix for no apparent reason?

Answer 1

Update:
Well, I did some more searches and testing on this, and it turns out that they all lie about the MIME type (never trust any information sent by the client, I know).
I checked a lot of files with different encodings (created using libjpeg)

Official MIME Type for jpeg files: image/jpeg

But some applications (especially MS Internet Explores, as well as Yahoo! mail) send jpeg files as image/pjpeg

I thought I knew pjpeg stands for "progressive" jpeg. It turns out that progressive / standard coding has nothing to do with it.

MS Internet explorer sends all jpeg files as pjpeg regardless of the contents of the file.

The same applies to citrix: all jpeg files sent from the citrix client are specified as image/x-citrix-pjpeg MIME type.

The files themselves are not affected (identical before and after loading). So it turns out that the difference in the MIME type is just an indication of the software used to send the file?

Why do people come up with a new type of MIME if there is no difference in the contents of the file?

Answer 2

image/x-citrix-pjpeg appears to be a MIME type sent by images that are exported from a Citrix session.

I did not encounter differences in formats between them and ordinary JPEG files. Most image conversion utilities will process them in the same way as regular pjpeg, after adding an appropriate rule of type mime.

It is possible that in the Citrix session there is some internal magic running on jpegs that leads them to create this mime type, which they leave in the file when exporting from their systems, but this is just my guess. As I said, I did not notice any actual differences in the format from the random files in this format that we get.

Answer 3

The next I came to find out what it is, this is a stream. Hope this helps.

http://forums.citrix.com/message.jspa?messageID=713174

Answer 4

For some reason, when users launch Internet Explorer through Citrix, it changes the mime type for GIF and JPG files.

 JPG: image/x-citrix-pjpeg GIF: image/x-citrix-gif 

Based on my testing, PNG files are not affected. I do not know if this is an Internet Explorer or Citrix issue.

Answer 5

This is due to a feature of Citrix called SpeedBrowse, which intercepts jpeg and gifs on server side [Citrix] web pages, so that it can send them entirely through ICA (Citrix Remote Access Protocol) - this is more efficient than screening them. As suggested in a previous post, this is done by marking images with a modified mime type.

IIRC intercepts FindMimeFromData in IE to change the mime type on the fly, but this applies to uploaded files and also loads alone - surely an error.

Answer 6

From what I remember, the Progressive JPG format is one that would allow a higher resolution image to be displayed as the file was uploaded. I don’t quite understand the details, but if you remember that during the set days, some files will appear blurry and then better and eventually completed as they are downloaded. To do this, the data must be sent in a different order than JPEG will normally be sent.

The actual data, as soon as you view it, is identical, it is simply sent in a different order. I myself forgot that the JPEG encoding itself groups pixels very well in different ways.