#5 Page resolution

[d4rk]

First of all, the library is excellent.

Would it be possible to add an option to set page
resolution in addition to the page size? For example,
if I am inserting a high resolution image (say from a
scanner that scanned at 300dpi),then the image size
would be pretty high, but I would still like the image
to be displayed in a 8.5x11in document, so if the page
resolution is increased to 300dpi, then the image will
display correctly.

Thanks and again, keep up the excellent work!

Cheers!

[LeslieM]

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Hi CodeLogic,

I think that pages are fixed at 72 DPI as per the PDF
standard (I could be wrong though).

Now I had the same problem and with painful trial and error
realised that pdf_contents_concat() can actually rescale
the image for you - I still have not worked out Parameters
3 & 4 but suspect they are to do with image rotation.

If you know the DPI then basically you can calculate a
scale factor and do the following

pdf_contents_concat(hImage, Width/ScaleFactor, 0, 0,
Height/ScaleFactor, X, Y);

I made a minor change to my copy of the static library to
allow me to get the PixelsPerMetre() of a PNG image as I
never know ahead of time the DPI. I have not made the
equivalent in jpeg as I don't need it but taking a look it
seems pretty simple to do.

Leslie.

[d4rk]

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Hi Leslie,

I think you are right, the PDF spec fixes the resolution at
72dpi (I discovered this later). I will check out
'pdf_contents_concat', thanks for the tip!

Cheers,
CodeLogic.

[Ade]

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Hi,

You can already achieve image resolution on a page at higher than 72 DPI by scaling the image when you draw it - note that this
does not re-compress the image or change the image in any way:

HPDF_REAL ScaleDPI(HPDF_REAL size) { return size * (72.0F / requiredDPI); }

HPDF_Page_DrawImage(page, image, x, y, ScaleDPI(HPDF_Image_GetWidth(image)), ScaleDPI(HPDF_Image_GetHeight(image)));

where requiredDPI can be 300 or whatever you require for your image.

This is more flexible as you can then mix and match image DPIs on the same page (eg a scanned image at 200 DPI, a screen capture at
96 DPI and an photo at 600 DPI)

Best regards,
Adrian Nelson