Rendering image size resolution

[aliya14]

Hello,
I had a query regarding the rendering resolution.If I render a view of 3 different image size ie 72 dpi, 150 dpi and 300 dpi. after that when I open this same rendered file in photoshop it shows the resolution as 72 dpi for all the 3 image sizes..why does this happen?
Regards
Aliya

[Henry D]

I think it has to do with what your settings are when you export your image. When you select "Export" you will notice in the "Export image" dialogue box that under "Format" and "Raster Image Quality" 72 is greyed out and appears to be the default. If you select "Zoom to" instead of "Fit to" under Image size you will be able to adjust the dpi. I hope that helps.

[hand471037]

Actually, it probably has something to do with the way DPI works. In Revit, DPI is set up based upon what the size of the image will be on a sheet.

DPI is always two things, the size of the final image and the Dots Per Inch of that image. Since it's DPI, it's always tied to directly to the size of the image. So an image that's 2.5" square at 300 DPI will be 5" square at 150 DPI. It's a strange way to think about image size or quality, since it's not a linear thing, it's a relational thing.

The way you can see the 'true' size of any image is to look instead at it's pixel width and height. It's *pixel size*. Revit shows you this next to the DPI setting on the render options bar.

That's why if you try to render a non-perspective view at 300 DPI it can crash out your machine, it will simply be too much info for the computer to deal with because your view might be 18" by 18" by 300 DPI... which means 5400 pixels on a side, or 29,160,000 total pixels!

This is also why doubling the DPI of an image quaduples the rendering time; an 5 x 5 image at 150 DPI is only 750 pixels on a side (562,500 pixels), where as a 5 x 5 at 300 DPI is now 1500 on a side (2,250,000 pixels - four times as much info).

So those views you might have could be the same *pixel size* but not the same *printing size*. I can't remember how Revit exports the images, but other rendering software will kick all images out at 72 DPI, but the pixel size will be whatever you set within the rendering software. So the image could be the right pixel size after all.

[SkiSouth]

Its in your preferences of Photoshop. Go to Edit, Preferences, Units and Rulers. Change the default SCREEN resolution from 72 to whatever you wish to use. The print resolution is on the same user interface and is normally defaulted to 300 DPI.

Photoshop is opening the image as commanded, interpreting the screen resolution and building the image to match the information available in the file opened.

Note you cannot make a 72 DPI Revit image look like a 300 DPI Photorealistic image by changing the resolution in photoshop, just due to lack of image information.If you are going to print, Try to process at 300 or 480 DPI, then save it. Photoshop will be able to handle that much better.

One good thing about Photoshop though, if you open a 300 DPI image file, and the photoshop screen image is 72 DPI, you can simply change the image resolution to get the file back the way it was generated in Revit. BE CAREFUL and either change the physical size of the image - say 8"x10" (which will be about 40-50 megs at 300 DPI0
or lock the physical memory size of the image before you up the resolution. If you have defaulted to 72 dpi with a 300 dpi file, the image size will be 30" x42" or some other odd size. You up the resolution of the image at that size (30x42) and Photoshop will CONSUME some memory - or crash your system.

Hope this helps.