PDF to PNG

Converting PDF To PNG

Typical ColorCaps input is a standard .png image file, but sometimes the line drawing we want to colorize is contained in a .pdf file. Printing CAD lines to a .pdf document allows easy viewing of the result to verify line thicknesses and generally check the content.

Adobe® Acrobat® provides the capability to print to .pdf, to convert a .pdf page to a high resolution .png image, and to perform other useful tasks, such as assembling a multi-page document from pages produced by different programs.

Here are some elevation CAD lines, printed from AutoCad® to .pdf:

We have loaded the drawing into Adobe Acrobat®. Here is the Acrobat SaveAs dialog showing the selection of the .png file type:

Once you select the .png file type, the Settings button becomes active. Press it to set the resolution of the .png image file you are creating.

If there are no colored lines, you can select monochrome, and the resulting .png file will be small and will process more quickly. Otherwise, you can leaave it as RGB.

What resolution do you use? Well, the size of the document is 18 x 24 inches. The size can be seen by clicking on File/Document properties. The standard image size for ColorCaps is 24 x 16 at 600 dpi, a size that provides plenty of pixels to work with. As the size of the document varies from this reference point, just the scale the resolution accordingly. 36 x 24 @ 400 dpi, 18 x 12 @ 800, 12 x 8 @ 1200, etc.

Another way to get the resolution is to start ColorCaps and click on Drawing/Page Size and key in the drawing dimensions. The resolution readout will tell you what resolution to use.

Once you have set the resolution, save the drawing in a convenient directory.

The file you have created is essentially the same as if it had been plotted it to .png using the TrueView or AutoCad plot utility. It has a 1:1 correspondence between the pixels in the file and the pixels ColorCaps will create from it. Load the drawing into ColorCaps using File/Import Plot Lines:

Adobe PhotoShop® or PhotoShop Elements® will can also load the .pdf file and save it to .png. Use the File/Open menu and navigate to the .pdf file and double blick on it. The following dialog will ask you how to rasterize the drawing:

Shut off the Anti Alias check box in order to create the clean, very high resolution bitmap. Choose GrayScale if there are no colored lines, otherwise leave it as RGB.

We selected 600 dpi resolution which gives us the 14400 pixels for the large dimension.

The important thing to remember about creating a big .png file for ColorCaps is the larger bitmap dimension needs to be approximately 15K pixels in order to preserve the CAD detail. In ColorCaps, you can print, create .pdf versions, or image versions in any size you want, as long as you started the colorization with enough pixels.

Acrobat® can print to .pdf, save .pdf to .png, and do other useful things with .pdf files. If you need Acrobat®, it's best to just get it unless you are confident a particular clone will work for you.

If you already have print to .pdf capability, then maybe PhotoShop® or PhotoShop Elements® is a good choice to do the conversion to the .png image needed by ColorCaps.

Keep in mind that some CAD programs, like the free Google Sketchup, can export directly to a high resolution .png file.