| Reading images from a socket [message #35879] |
Thu, 24 July 2003 23:33  |
Roberto Monaco
Messages: 11
Registered: August 2002
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Junior Member |
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I am trying to use a socket to read JPEG images from the Web.
I connect to the remote server, and get to the point of sending the GET to
request the image. But at this point I can not read from this unit by using
READ_JPEG (socket is not supported).
I tried to read it first into a buffer, and then read it from the buffer
with READ_JPEG. But I have no idea how to dimension the buffer correctly
beforehand (how large the image is). Even if I make it large enough
READ_JPEG gives me error reading from the buffer (conflicting keywords).
Also, in this case I know it is a JPEG image, but in general I need to
understand the type of image I am reading into the buffer, which I do not
know (in the HTML I have only "img src=name" from where I have no idea).
Any hints?
Many thanks,
Roberto
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| Re: Reading images from a socket [message #35956 is a reply to message #35879] |
Sun, 27 July 2003 16:13  |
andrew.cool
Messages: 47
Registered: July 2003
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Member |
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"Roberto Monaco" <rmonaco@coresw.com> wrote in message news:<bfqivl$hk0vb$1@ID-201966.news.uni-berlin.de>...
> I am trying to use a socket to read JPEG images from the Web.
>
> I connect to the remote server, and get to the point of sending the GET to
> request the image. But at this point I can not read from this unit by using
> READ_JPEG (socket is not supported).
>
> I tried to read it first into a buffer, and then read it from the buffer
> with READ_JPEG. But I have no idea how to dimension the buffer correctly
> beforehand (how large the image is). Even if I make it large enough
> READ_JPEG gives me error reading from the buffer (conflicting keywords).
>
> Also, in this case I know it is a JPEG image, but in general I need to
> understand the type of image I am reading into the buffer, which I do not
> know (in the HTML I have only "img src=name" from where I have no idea).
>
> Any hints?
>
> Many thanks,
> Roberto
Hi Roberto,
You can't use Read_JPEG, or any of the other image reading routines
over
a Socket.
What you can do is just read the image file as a sequence of bytes.
Something like this :-
Openw,outlun,'my_new_image.tmp',/GET
x=0B
While not EOF(socket_lun) Do begin
ReadU,socket_lun,x
writeu,outlun,x
End
Free_lun,socket_lun
Free_lun,outlun
Then use IDL's QUERY_IMAGE function to find out what sort of
image 'my_new_image.tmp' really is. Rename the .tmp file to suit.
That easy! ;-)
Andrew
(FTP using IDL is also possible. In fact easier, because you can
readily return the filesize before you download it.)
The QUERY_IMAGE function determines whether a file is recognized as a
supported image file. QUERY_IMAGE first checks the filename suffix,
and if found, calls the corresponding QUERY_ routine. For example, if
the specified file is image.bmp, QUERY_BMP is called to determine if
the file is a valid .bmp file. If the file does not contain a filename
suffix, or if the query fails on the specified filename suffix,
QUERY_IMAGE checks against all supported file types. If the file is a
supported image file, an optional structure containing information
about the image is returned. If the file is not a supported image
file, QUERY_IMAGE returns 0.
Syntax
Result = QUERY_IMAGE ( Filename[, Info] [, CHANNELS=variable] [,
DIMENSIONS=variable] [, HAS_PALETTE=variable] [, IMAGE_INDEX=index] [,
NUM_IMAGES=variable] [, PIXEL_TYPE=variable] [,
SUPPORTED_READ=variable] [, SUPPORTED_WRITE=variable] [,
TYPE=variable] )
Return Value
Result is a long with the value of 1 if the query was successful (the
file was recognized as an image file) or 0 on failure. The return
status will indicate failure for files that contain formats that are
not supported by the corresponding READ_* routine, even though the
file may be valid outside the IDL environment.
Arguments
Filename
A scalar string containing the name of the file to query.
Info
An optional anonymous structure containing information about the
image. This structure is valid only when the return value of the
function is 1. The Info structure for all image types has the
following fields:
Tag Type
CHANNELS Long
DIMENSIONS Two-dimensional long array
FILENAME Scalar string
HAS_PALETTE Integer
IMAGE_INDEX Long
NUM_IMAGES Long
PIXEL_TYPE Integer
TYPE Scalar string
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