How to calculate image size for printing

zutty

Senior Member
I'm a bit confused as to how to calculate image size and resolution for printing an image. Say I want to print out an image to a 14x10 inch size, with at home or a lab. What should the image size be? I usually shoot in RAW and then export to jpg, but I can't figure out what size/resolution the jpg should be or if it should be a jpg at all. Any help is greatly appreciated.
 

480sparky

Senior Member
Most labs & printers cannot print .NEFs or any other raw format. JPEG is the format to print.

Not sure what you're asking about 'image size'.
 

zutty

Senior Member
I mean that when you transfer the raw photo from NEF to jpg in Lightroom, what size to make it so that the lab will have the full image yet have the best possible quality. If I set it to say 240 resolution what size will be correct for say a 10x14 inch print without the lab cropping it like they seem to do.
 

WayneF

Senior Member
I'm a bit confused as to how to calculate image size and resolution for printing an image. Say I want to print out an image to a 14x10 inch size, with at home or a lab. What should the image size be? I usually shoot in RAW and then export to jpg, but I can't figure out what size/resolution the jpg should be or if it should be a jpg at all. Any help is greatly appreciated.

It can be a High Quality JPG to be printed... Like JPG Quality at least 8, better 9, in a 1 to 10 range.
TIF files are fine too, but it is much larger on the internet, and not all print labs accept TIF. Nothing wrong with High Quality JPG for printing.

The normal and ideal printing resolution is 300 dpi (pixels per inch). Some people say ppi, and some say dpi. I'm an oldtimer, I say dpi. :) Same thing in this context.

Whatever your inches, you need about 300 pixels per inch for that dimension.

This means to print 14x10 inches, you need to provide about

(14 inches x 300 dpi) x (10 inches x 300 dpi) = 4200 x 3000 pixels. It need not be exact, but roughly this ballpark, within + or - 15% or 20% perhaps.

If you don't have that many pixels, fewer will work, but hopefully up near 200 pixels per inch. Many commercial print labs print 250 dpi anyway.

Image and paper SHAPE confuses many. For a silly but obvious example, if your image was rectangular but the paper was circular, the shapes simply don't match. Same for paper, some sizes like 6x4 inch prints are long and skinny, where 8x10 is shorter and wider.. Different shapes. Your image shape needs to match your paper shape.

Note that your uncropped DSLR image is the SHAPE 3:2, which would scale to 15x10 inches, so you will have to crop the ends slightly to match the 14x10 paper shape. If you don't crop it first, the paper shape will crop it, but if you do it first, you get to see and approve the right crop first, so you know what is going to happen.

More about this sizing concept at Image Resize - Cropping, Resampling, Scaling

I am being brief, hoping the link is "how to" ,but I am very happy to answer any questions.
 

zutty

Senior Member
Thank you so much Wayne. That really helps. It's just confusing to me when I shoot in RAW/NEF on my camera to try and get the best quality possible and then have to reduce that quality to get it printed out. Thanks again!
 

480sparky

Senior Member
Thank you so much Wayne. That really helps. It's just confusing to me when I shoot in RAW/NEF on my camera to try and get the best quality possible and then have to reduce that quality to get it printed out. Thanks again!



8-bit JPEGs contain more data than the average human eye/brain is capable of discerning.
 

Rick M

Senior Member
When I export from LR, I just leave the IQ at 100 and it exports the largest size Jpeg it can. The file size will vary depending on the image. I've printed 16x24's from 11mb images.
 

zutty

Senior Member
Raw gives you the most data to edit with. JPEG is the end result.
Understood, of course...I am just trying to determine what level, size, resolution and all other variables of the jpg format to print with. I still don't understand what pointing out the eye/brain's discerning capacity has to do with my question.
 
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Fred Kingston

Senior Member
In LR, use the Export module to export a NEF image to JPEG... Scroll down the dialogue, and you can define the size of the image by selecting dimensions and putting in the dimensions using either inches or pixels... Define the quality by putting in the appropriate pixel density... Most print services can do 240dpi, and screen is fine at 72dpi

LR will create the correctly sized image based on your input...

The Export module gives you better control than the Print module for creating files to send to a printer....
 

480sparky

Senior Member
Understood, of course...I am just trying to determine what level, size, resolution and all other variables of the jpg format to print with. I still don't understand what pointing out the eye/brain's discerning capacity has to do with my question.

Merely pointing out that an image with an 8-bit color depth (JPEG standard), has more than enough information to make an acceptable print. Adding more data to the file will not make the image better.... it merely makes the file larger. That's part of the reason why most labs won't handle raw files..... the extra color depth cannot be printed.
 

zutty

Senior Member
In LR, use the Export module to export a NEF image to JPEG... Scroll down the dialogue, and you can define the size of the image by selecting dimensions and putting in the dimensions using either inches or pixels... Define the quality by putting in the appropriate pixel density... Most print services can do 240dpi, and screen is fine at 72dpi

LR will create the correctly sized image based on your input...

The Export module gives you better control than the Print module for creating files to send to a printer....
That's exactly what I have been doing, but no matter what dimensions I put in the export field, when I go to the lab's site they crop my image a lot, or conversely tell me the image is too small or of too small a resolution. I can't seem to find that "sweet spot" so to speak.
 

yauman

Senior Member
Zutty, attached is a screen shot of the setting I use for exporting for printing. I shoot raw and export to jpg for screen or print. But if you want to print, first use the Crop (Develop screen) and crop to the size you want - eg 8x10 etc. This gives you control of the crop so you'll know exactly how it will show on your print out.

Here's the export setting you'll need:

1 Ask the printing service What is the Color Space. It's usually sRGB but some can take a bigger color gamut like Adobe RGB or even ProPhoto RGB or others. For exporting to Screen, ALWAYS use sRGB - browser will not display anything else.
2. Set Quality at 100% for printing. If you are exporting for screen set quality to 60% or 50% - no monitors can display more that because our brains cannot resolve it. Hugh difference in file size between 100% and 50% - try it - create one at 100% and another at 50% and see if you can tell the difference and see the file size difference. You will be amazed.
3.Ask the printing service What is their printing resolution. Most will print at 240ppi and some will do 300ppi. Simple calculation: if you want an 8" wide print at 300ppi, you'll need 2400 pixels across. LR will do the calculation for you - see setting highlighted.
4 Set Size to the dimension you want and LR will handle the rest - but tell LR not to enlarge - it will pixelate.
5. Set sharpening to LOW for printing - glossy or matte depending on your printing request.

That's all and it should work fine with any printing services. Now, if the service complain that the file is too big, decrease quality from 100% to 85% or even lower, decreasing 5% each try until the file is small enough to upload to them.

Hope this helps.

LR ExportPrint.jpg
 

aroy

Senior Member
There are two methods.

1. Use native driver for the printer. That means you have to know which printer will be used. This is fine if you have one at home, then you load its driver and generate a print file for that printer. A similar exercise is done for professional printing. The printing lab can give you the printer make and model and their preferred driver. You install that driver and generate a print image file, send it to the printer. The major down side of this is the file size. Fine for professional jobs, where you go your self of send the data on a disk.

2. Use jpeg/TIFF file at the proper resolution. Normally high quality prints are at 300 DPI, but you can go down to 240 or even 200 DPI. The rest is calculation. For a 24MP image of 6000x4000 pixels the maximum print size at various DPI is

1. 300 DPI : 20.00" x 13.33"
2. 240 DPI : 25.00" x 16.66"
3. 200 DPI : 30.00" x 20.00"
4. 150 DPI : 40.00" x 26.66"

You can easily do reverse calculation for your cropped images. If your images are going to be mounted on a wall and viewed from a couple of feet, then 200 DPI is good enough, especially if you print on matte paper.
 

WayneF

Senior Member
That's all and it should work fine with any printing services

All except that process will not crop the Raw 3:2 format to fit 14x10 inch paper. Image shape will be 3:2, which is 15x10. The 14" paper itself will crop off the end, but if we do it first ourself, we can see our choices, and it will come as we expect.

The ACR crop tool will crop it first. 5x7 is same format as 14:10. Horizontal or vertical doesn't matter here, you can just drag it around. Or right click in its crop box, and there will be a Custom selection where 14:10 can be selected (but 5x7 is the same).

Not sure 14x10 is a standard print size offered, but some labs have a choice to print actual size, which means you cut off the blank white edge of larger paper.
 
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