[reportlab-users] embedded png image quality

[Robin Becker]

James Crone wrote:

> Hi,

> 

> I`m embedding a PNG image (a map rendered from MapServer) into a pdf 

> using reportlab with:

> 

> import Image

> from reportlab.pdfgen import canvas

> from reportlab.lib.pagesizes import portrait,A4

> 

> myImage = Image.open("C:/input_map_image.png")

> bgsMapCanvas = canvas.Canvas("C:/output_map_doc.pdf",pagesize=portrait(A4))

> bgsMapCanvas.setPageCompression(0)

> bgsMapCanvas.drawInlineImage(myImage,0,0,myImage.size)

> bgsMapCanvas.showPage()

> bgsMapCanvas.save()

> 

> 

> in the resulting pdf the embedded PNG image has been compressed 

> resulting in a loss of image quality and a fuzzy map document :-( . Is 

> it possible to prevent (PNG) images from being compressed when I add 

> them to a document?

> 

> Thanks in advance,

> 

> James

> 


I'm not exactly sure what you mean here. PDF natively supports jpeg which has an 
internal notion of quality. For other formats including opened PIL images we 
attempt to convert directly to 8bit rgb and pass that to PDF. As part of the PDF 
streaming process we apply some data filters to compress the size of the stream, 
but that shouldn't affect quality in any way. The compression that's controlled 
by  setPageCompression is completely lossless and only attempts to reduce the 
final document size(not quality). However, there may be some other kind of bug 
which means we're doing the wrong thing. I'm quite happy to look at your example 
if you send me the image. Don't reply here if the image is large just email me 
direct.
-- 
Robin Becker