I am still very new to at home scanning and Lightroom in general, I recently noticed that the dpi is being set in Lightroom when exporting, is there a recommended number for this? I do my scans with a Fuji x-t20 in raw and so far all of my photos have been exported at the default 72 dpi.
The dpi that you choose (or LR chooses!) when exporting a file makes no difference to the actual file, you can change it afterwards without affecting the quality at all assuming of course that you are exporting at the pixel dimensions that you need. There is a convention that 72 dpi is used for web/screen use and 300 dpi for printing but that is mainly for calculating the size at which the file will be viewed or printed respectively. Epson printers actually prefer 360 dpi for the best quality, at least mine does.
So if I can change it at any time how does it affect printing exactly? Also I don’t touch my resolution or anything when exporting, I leave it at the resolution given from the camera and after cropping, is this something I should be changing?
My example of 360 dpi for Epson printers is probably just confusing the issue here, I was just trying to think of a situation where the dpi setting actually made a difference. It’s not a good example though because it’s just a setting in the ‘Print’ module of Lightroom, I’m not exporting the file and it’s just an anomaly with how Lightroom seems to interact with the Epson printer driver.
At one time you needed to upload web images at 72dpi or else they were displayed at the wrong size but I’m pretty sure that doesn’t matter anymore.
I think that you’re saying that, apart from cropping, you don’t change the size of the image ( i.e the pixel dimensions) when exporting and that’s fine, if you wanted to you could easily setup a Lightroom preset that would set the resolution to 300 dpi (actually ‘pixels per inch’ in fact) but again, I doubt that it matters. My main point is that you don’t need to worry that you’ve exported your files at 72 dpi up until now.
Lightroom’s default export settings list 72 pixels/inch.
This “historic” value was the resolution of typical CRT screens and is nowadays mostly used as mentioned by @Harry above.
For printing, set a value of around 300 PPI (another historic value) and see what the printer makes of it - if the setting is used at all. A 4000x6000 pixel image should print 20 inches wide with a setting of 300 PPI, no matter what your printer’s DPI (dots per inch) technical specification might be.
Note that your printer driver can present values in DPI or PPI and most drivers allow to print to fit, which means that the driver will do the necessary math to fit your input PPI to the printer’s DPI and the desired image size.
The PPI values at which you export your raw captures matter to ultimate image quality. Firstly, you need to be clear about the purpose to which you are exporting the file. If it were for monitor viewing over the Internet, most of today’s displays have resolution in the range of 100~110 PPI, so setting your resolution within this range will result in predictable portrayal of linear dimensions on peoples’ displays. Lightroom also allows you to set the image linear or pixel dimensions at whatever PPI setting you choose. So you should do this too. A common setting would be say 1000 pixels at 100 PPI for the long dimension, which provides a 10 inch spread on a 100 PPI display. (1000/100=10)
If your export intent is, say, for printing with an Epson professional printer, for most general photographic purposes the input resolution to the Epson driver should be 360 PPI (300 for Canon professional printers). Again, you should also specify the largest linear dimensions you want for the print. There would usually be either too few or too many pixels in your image file relative to the PPI and linear dimensions you select. In all these cases, either Lightroom or the printing system will resample the data to be in the form the printer requires for processing and printing the file. The common advice in this regard is that resampling in Lightroom will produce somewhat higher quality than resampling in the printing system. This is why you want to specify the 360 PPI resolution in the Lightroom export dialog, because if you do not, the printing system will do so.
Before you proceed it is good to check what the native resolution of the file will be at your desired linear dimensions. The reason is that the native resolution at the chosen dimensions should be no less than 180 PPI. Below this value you may find that the call on resampling up to 360 visibly impairs image quality. In cases where PPI is less than 180, you should bring it up to at least that value by reducing linear dimensions. You can do this checking in the Lightroom Print module by unchecking the Resolution box and making sure you have turned on the Info for Print dimensions.
It doesn’t. All it does is set a value of some metadata fields.
You can prove this yourself. Export an image. Change the DPI and only the DPI and export the image again. The images will be identical. If you use something like Exiftool you’ll see the metadata will have different timestamps and the values for “X Resolution” and “Y resolution” will differ. The bits that make up the image will be the same.
So what is it used for? It lets software calculate the size of an image IFF it is displayed or printed at the given DPI.
Thanks everyone for the help, I was worried all my previous photos were missing quality based on the DPI.
To be clear about this, changing resolution (PPI) can indeed affect print quality. In its RAW state, a RAW file has no particular PPI. It has pixel dimensions that reflect the pixel dimensions of the sensor. For example, a Sony a6300’s APSC sensor has fixed pixel dimensions of 6000 x 4000. That is the maximum amount of “native” information contained in the file. When you render this image, let us say into a TIFF for printing, you need to specify resolution. Let us say you are printing with an Epson professional printer that requires as one of its “native” resolution settings 360 PPI. In Lightroom, if you leave the pixel count alone and set the resolution at 360, the resulting linear dimensions of the TIFF will be (6000/360) x (4000/360) or 16.7 inches x 11.1 inches. So far, you have not resampled the photo, you have given it only linear dimensions at the “native” resolution for an Epson printer.
Suppose, however, you had set the resolution at 240PPI. Your large dimension now becomes 6000/240 = 25 inches rather than 16.7 inches and the small dimension 4000/240 = 16.7 inches rather than 11.1. Suppose further that these are the linear dimensions at which you wish to print. You can select those dimensions for print, but then the photo will be resampled to 360PPI either in Lightroom (if you print from Lightroom) or in the printing system to conform with the input requirement of the printer driver. Resampling does affect image quality; remember: depending on the direction of the resampling, it either invents or destroys data in your rendered image file. Fortunately today’s resampling algorithms are so good that we have latitude in the extent of resampling before deterioration of image quality becomes noticeable or disturbing. As I mentioned above, I would avoid having to resample from below 180 to get to 360. Upward of 180 I can normally live with.
Best practice is to know the maximum print size you intend to print and keep those dimensions and the PPI resolution inside of a range that will still produce good outcomes from any resampling that needs to occur depending on your particular combination of linear dimensions and PPI, understanding that you are always starting from a fixed number of “native” image pixels and any resampling either invents or sheds data, which depending on the specific settings, can affect visible image quality in the print.
DPI/PPI is a function of your output device. Your printer is 300 or 360 or 240 or whatever. Nothing you put in the metadata will change the physical makeup of your printer.
The 16.7 vs 25 inches in your example is a calculation based upon the number of available pixels and the DPI/PPI in the metadata. It tells you how big of an image can be printed at the given DPI/PPI before the printer has to start interpolating pixels. But you don’t have to print at that size. I can set the PPI of a 6000x4000 image to 10,000 then print a 6" x 4" image. Setting the value changed nothing.
IMHO a best practice is to avoid resampling whenever possible. If you need to print something larger than the number of available pixels set the DPI/PPI to the physical value used by your printer. That way your printer will interpolate (make up) the least amount of pixels/dots necessary.
If you are exporting to some other format and not printing the value is used to fill in the metadata fields of the resulting image file. What happens after that depends upon what software you use to further process the image.
Nobody is talking about changing the physical make-up of the printer.
Yes it’s good to minimize the amount of necessary resampling, but within quite a range these days it’s tolerable. When you do need to resample, the quality of the result will be better if this were done in Lightroom than by the printing system.
One of the really nice things about NLP is that we can stay within a raw workflow from start to finish. An NLP-processed negative can be sent to print, without rendering the image, using the Lightroom controls for setting linear dimensions and resolution (PPI) which latter should match that required by the printer. Within certain limits Lightroom resampling will produce very good results.