Re: [Scopes] BMP image record??

[Pavel Masloff <pavel.masloff@gmail.com>]

Hey Matt,

Thanks for sharing! I can't make your code work, though. Every time I get some gibberish image, You might have forgotten to convert int to string?
I am using the following script.
Image file -> waveform:

import Image
import StringIO

from epics import PV
f = open('hello.bmp')     #source image file

data = "">
chan = PV ('file')
chan.put(data)

Waveform -> image file:

import os, sys
import Image
import StringIO
from epics import PV

chan = PV ('file')     #waveform pv
data = "" #waveform.val

sdata = ''.join(chr(x) for x in data)      
sfile = StringIO.StringIO(sdata)
im = Image.open(sfile)
im.save("yoyo.bmp")
im.show()


Another thing I can't understand - the Intensity widget in BOY. I don't know how to set its properties. I set PV name, Data height, Data width, Max, Min. And get an ugly image.

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



On Mon, Apr 30, 2012 at 6:59 PM, Matt Newville <newville@cars.uchicago.edu> wrote:

Hi Pavel,

Since you mentioned pyepics and numpy, I'll jump in to recommend a
slightly different waveform -> Image conversion using these:

   import Image
   import epics

   waveform_pv = epics.PV('xx:waveform.VAL')
   waveform = waveform_pv.get()  # will be a numpy array of unsigned ints
   # to get a truncated waveform, pass in the length you'd like:
   #     waveform = waveform_pv.get(count=400)

   width = ??     # that is, you'll have to assert this here.
   height = len(waveform)/width

   image = Image.frombuffer('L', (width, height), waveform, 'raw', 'L', 0, 1)
   image.show()

where you'll have the know the image height and width somehow to
unravel the 1-d waveform.   The Image.frombuffer() call is slightly
cryptic, but documented ('L' means 8-bit greyscale -- if you're
waveform held RGB data from a color camera, you'd change that here to
get a color image), and is faster than converting to a string and then
using Image.open().

--Matt

--
Best regards,


Pavel Maslov, MS
Controls Engineer at Pulsed power Lab
Efremov Institute for Electro-Physical Apparatus
St. Petersburg, Russia

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