Bad bad, don't copy code.

Create a function with the code you copied.

Also you changed 
OutputDev::drawImageMask(state, ref, str, width, height, invert, interpolate, inlineImg);
to 
OutputDev::drawImage(state, ref, str, width, height, colorMap, interpolate,
			 maskColors, inlineImg);
in the #else branch

(In reply to comment #1)
> Bad bad, don't copy code.
>
> Create a function with the code you copied.

The core of the PNG code here - the internal loop used to convert the bitmap into row for PNGWriter with comment "convert bits into a bytes for PNG" - is unfortunately unique. If you have any ideas how to make the two PNG writers into single function, I will do it.

At the moment I see that the image file name generation code and probably the file opening (to move away the error handling) can be separated into a new method.

Suggestions are welcome.

> Also you changed 
> OutputDev::drawImageMask(state, ref, str, width, height, invert, interpolate,
> inlineImg);
> to 
> OutputDev::drawImage(state, ref, str, width, height, colorMap, interpolate,
>              maskColors, inlineImg);
> in the #else branch

My bad. Will fix.

Created attachment 58273 [details] [review]
the patch, v2

Updated patch. Changes:

1. Fix the stupid copy-paste error OutputDev::drawImageMask()
   vs. OutputDev::drawImage()

2. Introduce a new PNG writing method, similar to drawJpegImage(), prototype:

void HtmlOutputDev::drawPngImage(GfxState *state, Stream *str, int width, int height,
                                 GfxImageColorMap *colorMap, GBool isMask)

which can write both RGB and MONOCHROME images. More parameters, since unlike
the jpeg counterpart, it has to do actual image creation.

3. Replace the PNG code in methods HtmlOutputDev::drawImage() and
   HtmlOutputDev::drawImageMask() with a call to HtmlOutputDev::drawPngImage() method.

Created attachment 58274 [details] [review]
the patch, v3

Same as the v2, but add the forgotten `#ifdef ENABLE_LIBPNG` around the body of the new function.

Please use ImageStream, there's no point in you doing the bit to byte conversion when ImageStream does it for you, and since the other part of the if also uses a ImageStream will surely allow you to share more code

Created attachment 58348 [details] [review]
extract monochrome images as PNGs, the patch, v4

Applies to the master.

Changes, compared to the previous version of the patch:
- use ImageStream to also read the monochrome rows
- add HtmlOutputDev::createImageFileName(const char *) method to create image file name.
- use the createImageFileName() method in both drawJpeg/drawPng methods to remove the old copy-paste.

Pushed