[reportlab-users] Optimizing greyscale and bilevel images

[Glenn Linderman]

On 12/28/2011 3:00 PM, Jesus Cea wrote:

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> Checking pdfgen/pdfimages.py, grayscale JPEG files are detected and

> used, but any other imagefile is converted to RGB.

>

> I have bilevel PNG files that when printed as PDF using reportlab are

> expanded THREE times.

>

> Seems quite trivial to detect "1", "L" and indexed files in PIL

> images, and generate optimized representation. Supporting "1" or "L"

> natively seems to be 5 lines of code or less.

>

> Are you interested in a patch?.

>

> Grayscale seems trivial. Bilevel seems easy. Indexed... I am not

> familiar with PDF format, and reading the spec it is not very clear to

> me how to do it, beside the ability of PDF supporting this.

>

> PS: I am using ReportLab 2.4.


In my work with bilevel images, I have found that TIFF with Group 4 
compression seems to produce the smallest files with lossless 
compression, or DJVU even smaller, but I think just slightly lossy.  I 
think the bilevel compression used by PDF is also Group 4?

Am  I correct that PNG doesn't support Group 4 compression, or am I 
missing an option that would allow bilevel PNG files to be as small as 
TIFF/Group 4 ?

I'd support the idea of your creating a patch :)  I'd even be willing to 
help test a Windows build of it.
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