Reportlab [ Platypus ] - Image does not render

Question

I am working on a report that includes a mixture of tables and images. The images [ graphs, actually ] are saved to the filesystem in .png form.

The method that actually renders the PDF is:

def _render_report(report_data):
    file_name = get_file_name() # generate random filename for report
    rpt = Report(settings.MEDIA_ROOT + os.sep + file_name)
    Story = []    
    for (an, sam, event), props  in report_data.iteritems():
        Story.append(Paragraph("%s - sample %s results for %s" % (an.name, sam.name, event.name), styles["Heading2"]))
        data_list = [['Lab', 'Method', 'Instrument', 'Unit', 'Raw Result', 'Converted Result', 'Outlier']]
        for (index, series) in props['frame'].iterrows():
            data_list.append(_format([
                Paragraph(Lab.objects.get(pk=series['labs']).name, styles['BodyText']),
                Paragraph(Method.objects.get(pk=series['methods']).name, styles['BodyText']),
                Paragraph(Instrument.objects.get(pk=series['instruments']).name, styles['BodyText']),
                Paragraph(Unit.objects.get(pk=series['units']).name, styles['BodyText']),
                series['raw_results'],
                series['results'],
                series['outlier']
            ]))
        table = Table(data_list, colWidths=[45 * mm, 35 * mm, 35 * mm, 25 * mm, 35 * mm, 35 * mm, 35 * mm], repeatRows=1)
        Story.append(table)
        Story.append(PageBreak())

        if props['graph'] is not None:
            Story.append(Image("/tmp/%s" % props['graph'], width=10 * inch, height=6 * inch))
            Story.append(PageBreak())
    rpt.draw(Story, onFirstPage=setup_header_and_footer, onLaterPages=setup_header_and_footer)
    return file_name

Background Information

• The page is set up as an A4, in landscape orientation
• My development environment is a virtualenv; PIL 1.1.7 and reportlab 2.6 are installed and functional

• The "Report" class used above is simply a thin wrapper around SimpleDocTemplate that sets up some defaults but delegates to SimpleDocTemplate's build implementation. Its code is:

  class Report(object):
      def __init__(self, filename, doctitle="Report", docauthor="<default>",
          docsubject="<default>", doccreator="<default>", orientation="landscape", size=A4):
          DEFAULTS = {
              'leftMargin' : 10 * mm,
              'rightMargin' : 10 * mm,
              'bottomMargin' : 15 * mm,
              'topMargin' : 36 * mm,
              'pagesize' : landscape(size) if orientation == "landscape" else portrait(size),
              'title' : doctitle,
              'author' : docauthor,
              'subject' : docsubject,
              'creator' : doccreator
          }
          self.doc = SimpleDocTemplate(filename, **DEFAULTS)
  
      def draw(self, flowables, onFirstPage=setup_header_and_footer, onLaterPages=setup_header_and_footer):
          self.doc.build(flowables, onFirstPage=setup_header_and_footer,
              onLaterPages=setup_header_and_footer, canvasmaker=NumberedCanvas)
  

What I have already looked at

• I have confirmed that the images exist on disk. The paths are fully qualified paths.
• PIL is installed, and is able to read the images correctly
• The space assigned to the image is adequate; I have confirmed this by calculation. Also, if I increase the image size, ReportLab complains about the Image Flowable being too large. The current dimension should fit.
• I have tested with and without the page breaks; they do not seem to make any difference

The Problem

The table, headings and page templates render OK but the images are blank. Earlier today, I had encountered this issue [ when setting up the templates used by this report ]. The workaround was to use canvas.drawInlineImage(... in place of canvas.DrawImage(... . It therefore looks as though there is an issue with my setup; I could use some pointers on how to debug it.

Update

I was able to apply a variant of the same workaround used in this linked question ( use canvas.drawInlineImage in place of canvas.drawImage. I subclassed `Image' as follows:

class CustomImage(Image):
"""
Override - to use inline image instead; inexplicable bug with non inline images
"""
def draw(self):
    lazy = self._lazy
    if lazy>=2: self._lazy = 1
    self.canv.drawInlineImage(self.filename,
        getattr(self,'_offs_x',0),
        getattr(self,'_offs_y',0),
        self.drawWidth,
        self.drawHeight
    )
    if lazy>=2:
        self._img = None
        self._lazy = lazy

The only change from the "stock" Image class is in one line - using self.canv.drawInlineImage where there was self.canvas.drawImage before. This "works" in the sense that the images are finally visible in my PDF. The reason why drawImage is not working still remains a mystery.

I have tried @PedroRomano's suggestion ( to make sure the images RGBA ), and even tried JPEG images instead of PNGs. These did not make a difference.

Answer 1

I eventually brought this matter to a close by using a custom Image subclass:

class CustomImage(Image):
"""
Override - to use inline image instead; inexplicable bug with non inline images
"""
def draw(self):
    lazy = self._lazy
    if lazy>=2: self._lazy = 1
    self.canv.drawInlineImage(self.filename,
        getattr(self,'_offs_x',0),
        getattr(self,'_offs_y',0),
        self.drawWidth,
        self.drawHeight
    )
    if lazy>=2:
        self._img = None
        self._lazy = lazy

Saving the graphs in vector graphics formats eg EPS, saving as JPEG, saving as PNG with and without the alpha channel all did not seem to make a difference.