RenderPage DPI from current PDF

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   Hi,
I have an app which creates a PDF with exactly one image / page (like scanned PDF) using RenderPageToStream/AddImageFromStream. Now when somebody adds some text/annotation/etc to it, I want to 're-render' the page into a new one image / page PDF.

However I don't know the DPI of the current PDF or the image embedded to it. Can that somehow be retrieved from PDF information (media box, dropbox, etc)?

Your help is appreciated!

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Chopinke Members Profile Find Members Posts Team Player Joined: 29 Apr 14 Status: Offline Points: 24	Post Options Post Reply Quote Chopinke Report Post Thanks(0) Quote Reply Topic: RenderPage DPI from current PDF Posted: 10 May 14 at 6:01AM
	Hi, I have an app which creates a PDF with exactly one image / page (like scanned PDF) using RenderPageToStream/AddImageFromStream. Now when somebody adds some text/annotation/etc to it, I want to 're-render' the page into a new one image / page PDF. However I don't know the DPI of the current PDF or the image embedded to it. Can that somehow be retrieved from PDF information (media box, dropbox, etc)? Your help is appreciated!

AndrewC Members Profile Find Members Posts Moderator Group Joined: 08 Dec 10 Location: Geelong, Aust Status: Offline Points: 841	Post Options Post Reply Quote AndrewC Report Post Thanks(1) Quote Reply Posted: 12 May 14 at 3:27AM
	Chopinke, PDF files do not have a DPI value which is why they can be scaled and zoomed. It is possible to extract the DPI of the images in the PDF but a PDF could have multiple images with various DPI values. Here is some code to extract the DPI values from the images on a page. // This will extract the DPI of the image at the size it is drawn onto the PDF page. // Now that the image is draw we can calculate the number of pixels per inch that it was drawn at. int id = QP.GetPageImageList(0); for (int i = 1; i <= QP.GetImageListCount(id); i++) { int widthInPixels = QP.GetImageListItemIntProperty(id, i, 401); int heightInPixels = QP.GetImageListItemIntProperty(id, i, 402); // Default measurement units are in points. 72points = 1 inch. double imageWidth = Math.Abs(QP.GetImageListItemDblProperty(id, i, 503) - QP.GetImageListItemDblProperty(id, i, 501)); double imageHeight = Math.Abs(QP.GetImageListItemDblProperty(id, i, 508) - QP.GetImageListItemDblProperty(id, i, 502)); double dpix = widthInPixels / imageWidth * 72; double dpiy = heightInPixels / imageHeight * 72; MessageBox.Show("DPIX = " + dpix.ToString() + " DPIY = " + dpiy.ToString()); } Andrew.

Chopinke Members Profile Find Members Posts Team Player Joined: 29 Apr 14 Status: Offline Points: 24	Post Options Post Reply Quote Chopinke Report Post Thanks(0) Quote Reply Posted: 12 May 14 at 9:15PM
	Thanks, it works! On an example I receive a horizontal 96dpi, but for some reason on the vertical I get 96.000121something... However if I ROUND it my software works fine. Am I right to assume that when I load a PDF file it's current zoom level is its actual size = 100%?