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A
Augphoto
Participating Frequently
November 17, 2017
Question

Printing size confusion -

  • November 17, 2017
  • 2 replies
  • 2248 views

I am now massively confused.

I've been using Lightroom for years but never delved much into the Print Module.

Here is my dilemma - I have an image I would like to print as large as possible.  It is my understanding that the quality of the image is based largely on it's file size.  A 12MB file would obviously make a higher quality image then a 2MB file. OR, are the dimensions of the file more important?  If so, a 4000 x 3000ppi would print better than say a 2000 x 1500ppi file.  This seems logical.

But now, the confusion really sets in!!  If I use the Lightroom Print Module and choose 'print to file' the jpeg (which I believe most printers want) comes out much smaller.  I am assuming that NOW this forces me into a much smaller print if I'm to maintain anywhere near the same quality.  This is actually the second change in size in my workflow, thus it's really confusing to me.

     As an example - I have a digital image which I imported, cropped to 8x10 and enhanced to my liking. This file is shown as 5760 x 3840 is 30.3MB.  Actually               cropped is says is 4800 x 3840.  Fine so far.  Now, after bringing it into ONOne for further enhancements (and a little tighter crop) It comes back into Lightroom at a whopping 366.8MB with new dimensions of 4294 x 3436.  So far, Ive lost a little in the dimensions.  BUT now, when I set up print in the print module and choose 'print to JPEG file' it gets real crazy.  This file is now only 2.6MB and the dimensions are a measly 1440 x 1152.  I understand that the much smaller MB makes emailing to a printer manageable but if I am right the dimensions are suddenly impossible to work with when trying to get a quality print of a large size.

Obviously, my understanding and/or workflow is deficient in this area.  Any help would greatly be appreciated.

Also, is there an easy way (without jumping through mathematical hoops) to surmise how large a of quality print can be made based on the file dimensions and/or MBs?

Thanks in advance for any help which may be forthcoming.

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    2 replies

    J
    Jao vdL
    Community Expert
    November 21, 2017

    dj is as always correct. Ignore the file size. It can correlate with quality but is not a guarantor of quality.

    To get a superb print you need to get three things right. I. You need to get the image scaled to the right size. Usually you want to have a file of a resolution close to 300 pixels per inch. This means that if you are going to make a 8x12 print, you need to scale the image down (usually) to 2400x3600 pixels. Scaling your image down and applying output sharpening actually gives you a sharper looking print than sending a full resolution file so that brings us to II. You need to apply output sharpening at the output size and for the kind of paper you will be using. This is done in the print panel in Lightroom or in export. You do need to make sure to scale to the optimal printer resolution as done in I. and III. You need to get your color management right. The last is essential but I won't get into it.

    So if you use an online service, you should export to jpegs of quality 80 or higher (100 is overkill and cannot be detected in the final print by humans) scaled to the correct size and output sharpened and in a color profile that is correct for the printer/paper combination or what the print service requests.

    Tiff is good too, but if you get your color management right and use high quality jpegs, you cannot see the difference in the final print.

    A
    AugphotoAuthor
    Participating Frequently
    November 22, 2017

    Thank you.

    So I need to scale the image.  Is this what the file resolution area in the print module does?  This is where it changes the psi.  When I change that number is that considered scaling the image?

    If I do scale an image and do everything else you recommend it would still not guarantee a given print would be of quality in a large size, correct?  I know an image can vary in quality at the press of the shutter and that some are not alway technically corrector sharp, etc.  but this is not what I'm referring to.  I mean, if it qualifies as a good, sharp image from the get go and all the steps you laid out are taken.  How then do we know how large we can go with a print? (Sorry, I'm probably not wording this well). 

    In other words, if I have two very high quality digital files they may have different dimensions at the same 300ppi setting, right?  Even though they are both excellent to begin with there they would not necessarily both print well in a large print then?  If this assumption is correct what method does one use when deciding if a file will print well in a larger size?

    Again, I am quite sorry because I feeling that I am not wording my questions succinctly.

    J
    Jao vdL
    Community Expert
    November 22, 2017

    Augphoto  wrote

    Thank you.

    So I need to scale the image.  Is this what the file resolution area in the print module does?  This is where it changes the psi.  When I change that number is that considered scaling the image?

    Yes that's right. When you enter a resolution in the print module Lightroom will scale your image to that resolution on the final print.

    If I do scale an image and do everything else you recommend it would still not guarantee a given print would be of quality in a large size, correct?  I know an image can vary in quality at the press of the shutter and that some are not alway technically corrector sharp, etc.  but this is not what I'm referring to.  I mean, if it qualifies as a good, sharp image from the get go and all the steps you laid out are taken.  How then do we know how large we can go with a print? (Sorry, I'm probably not wording this well). 

    That's correct too. My post assumed that your source image is high enough quality to start with. dj gave an excellent example of how to know whether your image is good enough. The 300 ppi rule is valid for images seen at arm's length. If you print billboard size, you can get away with far lower resolution. The reason for this is that the human eye ideally has a certain resolving power that is expressed in a minimum angle that can be seen as distinct. For color vision this translates to around 300 ppi at arm's length but if you view a print from further away you don't need that much. Basically twice as far away: 150ppi, 4 times as far away, 75 ppi, etc. etc. I have printed 6 feet high images from an iPhone that people remark to me how incredibly sharp they are which is true as long as you don't stand too close ;-)

    >>In other words, if I have two very high quality digital files they may have different dimensions at the same 300ppi setting, right?  Even though they are both excellent to begin with there they would not necessarily both print well in a large print then?  If this assumption is correct what method does one use when deciding if a file will print well in a larger size?

    Use the math from dj above. Simply divide the dimension in pixels by the desired ppi such as 300 ppi and you will get the maximum size you can print for prints viewed at arm's length.

    >Again, I am quite sorry because I feeling that I am not wording my questions succinctly.

    This is hard stuff and it is why I teach a whole class on printing where this is all dealt with. Many (most!) people have trouble with this. Oftentimes simplistic rules such as you have to have 300 ppi! are just not right as they don't consider how the print will be viewed. Advertisement billboards never have that kind of resolution!

    D
    dj_paige
    Brainiac
    November 21, 2017

    Here is my dilemma - I have an image I would like to print as large as possible.  It is my understanding that the quality of the image is based largely on it's file size.

    A common misconception, but this is 100% incorrect. File size is meaningless in the context of determining the quality of an image.

    The quality of an image is based entirely on the number of pixels (width and height) in the image. Image size (not file size) is what you want to look at.

    Image size and file size are largely independent; one does not imply the other.

    A 12MB file would obviously make a higher quality image then a 2MB file.

    Possibly, and possibly not.

    If so, a 4000 x 3000ppi would print better than say a 2000 x 1500ppi file.  This seems logical.

    This is correct, except your units are completely wrong. An image that is 4000x3000 is pixels, not pixels per inch (ppi). Similarly, 2000x1500 is pixels and not ppi. Digital images do not really have a pixels per inch value; although such a number can exist in the file metadata, it is meaningless.

         As an example - I have a digital image which I imported, cropped to 8x10 and enhanced to my liking. This file is shown as 5760 x 3840 is 30.3MB.  Actually               cropped is says is 4800 x 3840.  Fine so far.  Now, after bringing it into ONOne for further enhancements (and a little tighter crop) It comes back into Lightroom at a whopping 366.8MB with new dimensions of 4294 x 3436. 

    As stated above, the size of the file is irrelevant. Meaningless. Doesn't tell you any useful information. Ignore it.

    This file is now only 2.6MB and the dimensions are a measly 1440 x 1152.  I understand that the much smaller MB makes emailing to a printer manageable but if I am right the dimensions are suddenly impossible to work with when trying to get a quality print of a large size.

    The size of the file is meaningless. Ignore it. I don't know how the dimensions dropped to 1440x1152, but this is usually because the user did something somewhere to either crop the photo or re-size the image. This decrease in the image size represents a possible mistake, and will result in a loss of quality if not corrected.

    A
    AugphotoAuthor
    Participating Frequently
    November 22, 2017

    Thank you greatly.

    I don't know how the dimensions dropped to 1440x1152, but this is usually because the user did something somewhere to either crop the photo or re-size the image. This decrease in the image size represents a possible mistake, and will result in a loss of quality if not corrected.

    I discovered my mistake.  Somehow the file resolution was changed in the print module.  Once I returned it to 300ppi the file dimensions  looked reasonable.

    I now totally get it that the file size is meaningless.  Thanks.  However, I should pay attention to pixels.  But if it's pixels per inch that counts the photo dimensions must surely factor in.  You say, "Digital images do not really have a pixels per inch value", so what do we base our decisions on?

    D
    dj_paige
    Brainiac
    November 22, 2017

    Printed photos have inches, and they have pixels, so therefore they have pixels per inch.

    The inches come from the size you want to print, for example if you want to print 4x6 inches. The pixels come from the image, if you have 2000x3000 pixels, then simple division gives you a pixels per inch of the printed photo of 500 pxiels per inch.

    Many people say you want 300 pixels per inch to get good printed quality, so a 4x6 needs 1200x1800 pixels. Some people say you can get away with 240 pixels per inch to get good quality, so a 4x6 needs ... Well you do the math.

    Larger size prints, for example 12x10 usually require fewer pixels per inch, you could get a good quality image at 180 or 150 pixels per inch. Some of this, of course, is judgment, but those are som simple guidelines.

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