The finest quality photo prints from digital photos will always be obtained by printing the original image as captured by the digital camera. This means printing the file with the image pixels unaltered, or without any image resampling. Pixel resampling rebuilds the actual image data through software manipulation, resulting in a degraded image quality. The greater the degree of resampling, the greater the loss in original image quality.
Photo enlargement of a digital photo can be performed without any original file resampling. The amount of enlargement possible depends on the original resolution, or pixel dimensions of the photo, how large the photo needs to be printed, and the processing software and printing system used. In this article I will address this issue considering use of only an image editing software such as Photoshop, and standard printer output as a typical desktop or medium format printer capable of print sizes ranging from 8x10 up to 12x18.
All digital cameras capture images in a format oversized from standard print or frame sizes. This is to accommodate for future photo cropping to balance or fine tune the final photo, and allow for possible adjustments to errors made when framing the photo before capture. To produce standard print or frame sizes, any digital photo will need to be cropped and there are two basic image formats with digital cameras.
Most "point and shoot" digital cameras produce an image with a 4:3 aspect ration. We consider this image format the "standard format digital camera" print size. Most SLR digital cameras produce an image with a 3:2 aspect ration. We consider this image format the "wide format digital camera" print size. These two different image formats vary considerably in the full image, uncropped image sizes default from the camera. The following link is a chart that illustrates the size differences of these formats at various print size ranges.
Photo enlargement, print formats and digital photo cropping.
There is a simple method you can utilize to produce photo enlargement and photo cropping to standard print sizes using your image editing software. For this example I will be using Photoshop CS for the methodology, although with any quality image editing software, the steps will be similar. I will process a 5 megapixel, standard format digital camera photo with a pixel resolution of 1944x2592 and an 8 megapixel, wide format digital camera photo with a pixel resolution of 2336x3504. Photo enlargement and photo cropping will be to the standard print sizes of 8x10, 11x14 and 12x18 to illustrate the process.
Both photo examples below are with the photo in landscape orientation, or the image long side being horizontal. For portrait orientation, adjust size entries appropriately.
Photo 01 - 5 megapixel standard format photo (1944x2592 pixels)
Photo 02 - 8 megapixels wide format photo (2336x3504 pixels)
Photo 01 - 8x10 photo enlargement with photo cropping:
Open photo file
Image > image size
Uncheck resample and enter 8 in the the document size height.
Creates an image 10.667w x 8h at 243 resolution > OK.
Select crop tool and enter in toolbar parameters:
Width: 10 in Height: 8 in Resolution: 243
To constrain crop to photo edges: view > snap to > document bounds
Drag crop box over entire photo and position as desired.
Click checkmark at top right of top toolbar to set the crop.
Your photo enlargement is to 8x10 at 243dpi, absolutely original image quality.
Photo 02 - 8x10 photo enlargement with photo cropping:
Open photo file
Image > image size
Uncheck resample and enter 8 in the the document size height.
Creates an image 12w x 8h at 292 resolution > OK.
Select crop tool and enter in toolbar parameters:
Width: 8 in Height: 10 in Resolution: 292
To constrain crop to photo edges: view > snap to > document bounds
Drag crop box over entire photo and position as desired.
Click checkmark at top right of top toolbar to set the crop.
Your photo enlargement is to 8x10 at 292dpi, absolutely original image quality.
Photo 01 - 11x14 photo enlargement with photo cropping:
Open photo file
Image > image size
Uncheck resample and enter 11 in the the document size height.
Creates an image 14.667w x 11h at 176.727 resolution > OK.
Select crop tool and enter in toolbar parameters:
Width: 14 in Height: 11 in Resolution: 176.727
To constrain crop to photo edges: view > snap to > document bounds
Drag crop box over entire photo and position as desired.
Click checkmark at top right of top toolbar to set the crop.
Your photo enlargement is to 11x14 at 176.727dpi, absolutely original image quality.
Photo 02 - 11x14 photo enlargement with photo cropping:
Open photo file
Image > image size
Uncheck resample and enter 11 in the the document size height.
Creates an image 16.5w x 11h at 212.364 resolution > OK.
Select crop tool and enter in toolbar parameters:
Width: 14 in Height: 11 in Resolution: 212.364
To constrain crop to photo edges: view > snap to > document bounds
Drag crop box over entire photo and position as desired.
Click checkmark at top right of top toolbar to set the crop.
Your photo enlargement is to 11x14 at 212.364dpi, absolutely original image quality.
Photo 01 - 12x18 photo enlargement with photo cropping:
Open photo file
Image > image size
Uncheck resample and enter 18 in the the document size width.
Creates an image 18w x 13.5h at 144 resolution > OK.
Select crop tool and enter in toolbar parameters:
Width: 18 in Height: 12 in Resolution: 144
To constrain crop to photo edges: view > snap to > document bounds
Drag crop box over entire photo and position as desired.
Click checkmark at top right of top toolbar to set the crop.
Your photo enlargement is to 12x18 at 144dpi, absolutely original image quality.
Photo 02 - 12x18 photo enlargement no photo cropping needed:
Open photo file
Image > image size
Uncheck resample and enter 18 in the the document size width.
Creates an image 18w x 12h at 194.667 resolution > OK.
No photo cropping needed. Default photo size from camera.
Your photo enlargement is to 12x18 at 194.667dpi, absolutely original image quality.
With the photo enlargement and photo cropping finished, the next step is to print the processed images. Most people have heard that you may need a dpi of 300 to print photos with satisfactory quality. This may or may not be necessarily true depending on your particular printer and printer driver software. What I would recommend doing is to try a little experimenting here. As said previously, the best photo print quality will come with the least amount of image resampling to boost image resolution or size.
First, I would try printing the enlargements at the final resolution in the examples above. If you are not satisfied with the results, only then I would boost the input file resolution. Many experts claim an input resolution of between 200 - 300 dpi should be sufficient. I would start at the low end of 200 dpi and resample the file to this number to keep the degree of resampling as low as possible.
To resample in Photoshop CS:
Open file
Image > image size
Check resample and enter 200 in document size resolution.
Click OK. Your photo is now the same size in inches at 200 dpi resolution.
Try printing again and see if this is enough resolution to produce a quality print. You can continue attempting different input resolutions by resampling the photo at different dpi's. When trying a new input dpi, always start with the original resolution file and do not use a version of the file you have already resampled. Every time an image file is resampled, it degrades the image quality more.
For more tips and advice on photo enlargement of digital photos, view this page:
Photo Enlargement Tips
The advice in this article is intended for those who use standard image processing and printing systems. Highly advanced digital processing and photo enlargement software systems such as the systems we use can yield much larger photo print sizes while maintaining absolute original image quality.