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.

Answer 2

The optimal solution would be to generate your graphs in a vector format like postscript that is supported by reportlab. A lot of UNIX software can do this out of the box, and on windows you can use the excellent PDFCreator.

If you have to use raster images for your graphs, try converting your images to JPEG format. Those can be easily embedded in a PDF file using the DCTDecode filter. (This is e.g. what jpeg2pdf does.)