Re: [Scopes] BMP image record??

[Rod Nussbaumer <bomr@triumf.ca>]

The data in a PNG image file will contain pixel data for the image, but 
not in a directly readable form, as the image data is stored in a 
compressed format. The size of the image file is therefore generally 
much smaller than the image itself. You will need to allow enough room 
in the waveform record and in $EPICS_CA_MAX_ARRAY_BYTE for the size of 
the file. You will probably need to determine empirically what size this 
is, recognizing that it is somewhat variable, depending on the exact 
content of the image, so selecting an arbitrarily large enough size is 
probably the best approach.

Without having the manual for your scope, I am only theorizing, but it 
is possible that the binary image data returned by the scope contains 
some scope-specific header which is intended to be stripped off before 
storing the image file data. This might also depend on other persistent 
settings within the scope, such as any 'HEADERS' and 'VERBOSE' settings.

   ---   rod.


Pavel Masloff wrote:
> Could you also explain to me how the trasformation image binary file ->
> waveform and back happens? As I understand an image is roughly a set of
> pixels each with its own color. There is also a header (which we don't
> need?) Then we read the file and forward every byte into the waveform
> record which is of type unsigned char (integers 0-255) with a size =
> 1byte. So in order to get an image out of the waveform we should break
> the waveform N times with an interval M (if our image dimensions are
> N*M). There is also a Color map which specifies what color our integers
> equal to.
> Now when we want to convert our waveform back to file we are using the
> chr(x) function, I don't know why.
>
> Next thing as you mentioned is the NELM field and
> EPICS_CA_MAX_ARRAY_BYTE variable. So if our image is say 400*300 24 bit
> BMP image, does it mean we should set NELM=400*300 and
> EPICS_CA_MAX_ARRAY_BYTE=400*300*24?
>
> I would be grateful to hear your comments.
> Thank you.
>
> Pavel