Image size and resolution

[blair]

What is the best image size and resolution to start with when creating a digital render? For example: If one is doing a photo montage what should one start with for the digital photo image size/resolution and the CAD modeled image size/resolution that will come in seperately? Should both be worked on at their original size/resolution and then integrated into one for later reduction if needed. Or, should they be reduced in size/resolution before work is started on one or both.

 

Our digital camera generates an original .jpg file size of +-3200 x 2400 pixels at a resolution of 72 ppi total and the .jpg size is 3.72MB. We print a CAD file to a Adobe PDF file, open it in Adobe Illistrator then export it as a Photoshop PSD file as using the following settings Color Model-RGB, Resolution-High (300ppi), Export As-Photoshop CS, Flat Image (marked), Anti Alias-Off”. This method generates the best quality we have found so far but may not be the pro best. When the line image is opened in Photoshop the .psd file is +-2700 x 2000 pixels at the resolution of 300ppi. The .psd file is 5.19MB before adding a white background layer. After adding the white background layer the size is 3.38MB. Is it good to work with both as is or should some things be changed before starting.

[Hector]

What is the best image size and resolution to start with when creating a digital render? For example: If one is doing a photo montage what should one start with for the digital photo image size/resolution and the CAD modeled image size/resolution that will come in seperately? Should both be worked on at their original size/resolution and then integrated into one for later reduction if needed. Or, should they be reduced in size/resolution before work is started on one or both.

 

 

 

There seems generally to be confussion with the concepts of resolution and number of pixels and quality of image.

 

What is really important is the number of pixels that define the image. It is the number of pixels and the number of bits asigned to each pixel (24 bits or 32 bits generally) what defines the size in MB of the file.

 

Resolution is irrelevant to the file size as it only defines the size at which pixels are printed.

 

The confusion comes as normally "resolution" is associated with the number of pixels. For instance,in your digital camera the higher "resolution" settings only mean a higher number of pixels. The higher the number of pixels the more detail you will get when zooming in on your image.

 

Say that you have an image with 3000 x 2000 pixels at 72 dpi. this means that when you print the image it will be 41.66 inches long by 27.77 pixels tall. Each pixel is 1/72 of an inch in width and height.

 

If you open that image in Photoshop and in "image size" you change the resolution to 300 dpi (YOU MUST turn off the resampling option), you will see how the size of the file does not change but the size of the image in cm or inches does change and now the image is smaller because each pixels meassures 1/300 of an inch. If you print it now, it will print samller than the previous version at 72 dpi.

 

However, and this is another source of confusion, if you turn on the "resampling option" you are not only changing the resolution but also changing THE NUMBER OF PIXELS in the image and the file size. As people normally change the resolution without caring about the "resampling" checkbox they see the image size grow and get the wrong conclusion that changing the resolution change the file size.

 

If you wnat to make a photomontage, take a picture of the site at the higher number of pixels you can. Assuming that you want to print at 300 dpi you will now beforehand how big your final image will be if you do the math as above. Then determine how big the render of your building will be regarding the image and define how big in pixels the image to render needs to be. And do the render acordingly

[mbr]

Try a search, Jeff wrote a good article about it a while back.

 

I'll have to reread it, but I am not sure why you are going through a long process to get to your digital photos. They can only be as good/hi res as you took them originally.

[Andy Hickes]

Blair

 

I work at approx 200 ppi at the size the final rendering will be printed out

(20x30, 24x36, or what ever). That is about 60M flat. I render out the CAD model to that size (if it is cover the whole rendering). I bring all the pieces (photos,linework, entourage, CAD model, etc) onto that base (upsample if I must). If the overall file gets too big I crop just the section i am working on and save as another file. When that part/detail is fishished I bring a flatten version of that crop back into original overall file. I save a lot of flattened versions of the overall also along the way to keep the file size down.

 

I print on an Epson printer and find 150ppi is large ehough to print with no pixellation. I work at the larger 200ppi just because I can get in closer.

 

Andy

[hockley91]

Hector,

 

Great explanation of resolution. That pretty much sums it up.