Resizing for large prints.

bass_junkie83

bass_junkie83

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Dave
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I use a 5d mk1 which outputs raw files of 4368x2912px @ 240ppi.

Normally I export two versions from lightroom, a resized copy for web use (generally 720px along the long side), and a non resized copy for printing. Generally I don't do many large prints so the original sized jpeg is more than sufficient for me not to have to think about it.

But if i want to print a large photo, I will need to resize the image so that it is larger than the original.

For example, I may want a 30x20" print, and the lab will request a minimum resolution of 300ppi. That equates to a 9000x6000px image.

As I am enlarging the originl file, I am concerned about the effect this will have on the overall quality, so would appreciate advice on how best to do this.

If i take the original file and change the resolution to 300ppi, this gives an image size of 5460x3640px, still short of the required. Is it really a simple case of changing the output size or do i need to be doing something more?
I will typically be using lightroom.

Thanks. :)
 
I would change the DPI only not the filesize.... But others may disagree so dont take mine as the definitive answer...
 
I crop mine in PS, set the crop tool to 30" x 20" and 300ppi
 
With lightroom, cropping dictates the aspect ratio, but not the actual output size. This is done upon export. So a little different to doing it in PS.


That's what i wasn't sure on. I see two options, there may be others I am not aware of.

Starting with the original file again of 4368x2912px @ 240ppi.

I can either,

1.
Increase the resolution to 300ppi, then increase the image sized to 9000x6000px.

or

2.
Increase the resolution to 500ppi, which in turn gives me an image size of 9100x6067px. A tad larger than needed so ok.
 
Last edited:
If you print a 30"x20" at 300ppi where the print process uses one pixel per dot (i.e. DPI=ppi), from a 4368x2912px print, someone somewhere is going to have to resize it to 9000x6000. That can be you or the print lab.

The last time I printed anything (through DSCL) I scaled my images so they were 300 x size in inches. I was printing 18x12 so that meant images that were exported from LR at 5400x3600 in size and I requested 18"x12" prints. In fact, with DSCL, the ordering process doesn't care about what DPI you have set in the file. You give it a file and tell it what size to print and it will tell you how good or bad they think the resultant image will be (in practice, even images that are 720x540 will print "acceptably" at 72ppi i.e. a 10"x8" print). The process will then scale your image so that for each inch you ask it to print, it will have 300pixels if you haven't done this already.
 
bass_junkie83 said:
With lightroom, cropping dictates the aspect ratio, but not the actual output size. This is done upon export. So a little different to doing it in PS.


That's what i wasn't sure on. I see two options, there may be others I am not aware of.

Starting with the original file again of 4368x2912px @ 240ppi.

I can either,

1.
Increase the resolution to 300ppi, then increase the image sized to 9000x6000px.

or

2.
Increase the resolution to 500ppi, which in turn gives me an image size of 9100x6067px. A tad larger than needed so ok.
Click to expand...

I tend to go for your option 1 - increasing both the PPI and Image Size in Lightroom together.
In terms of whether PS or LR are "better" at doing this depends on whether they use the same engine to upscale your images or not.... I would hazard a guess that the PS engine is better / more capable - though I have no evidence or proof to suggest that.

Ps - this PPI still confuses me. Other than file size, what is the downside to setting a PPI of say 900? If the printer can only print at max 300ppi, then surely its not going to matter?

What PPI do others use?
 
futureal33 said:
If the printer can only print at max 300ppi, then surely its not going to matter?
Click to expand...
You don't set ppi in the file, you set DPI. The problem with setting it to something other than what the printer accepts is that it then leaves the output down to the printing program. For example, say you have a 3000 x 3000 pixel image set at 900dpi and a printer capable of 300ppi. You could get:

  • a 10" x 10" print (300ppi, from 3000 x 3000)
  • A 3.3" x 3.3" print (900DPI interpreted as 900ppi from 3000 x 3000)

Setting the DPI to the same as the printer and outputting at the correct ppi (i.e. ppi of printer x desired image size) means there is no ambiguity as both calculations give the same result.
 
Personally I keep all my original edited Tiff files unsharpened on the PC at the native resolution of the camera and then when necessary resize to the enlargement size using Photoshop "image size" @ 300DPI - I then add sharpening. If the enlargement is pretty big, say 36x24inch, rather than resize in one hit I enlarge the file in 10% steps using "image size" , I read somewhere recently that this is the best way to retain image sharpness.

Simon
 
Don't do anything to the image, let the printers RIP do the work. You'll achieve nothing by enlarging it in PS except increase the file size.
 
Danny_Two said:
You'll achieve nothing by enlarging it in PS except increase the file size.
Click to expand...
and the ability to process it at the size that will be used for print which is important for sharpening....
 
Danny_Two said:
Don't do anything to the image, let the printers RIP do the work. You'll achieve nothing by enlarging it in PS except increase the file size.
Click to expand...

I use zenfolio to sell prints through my website.
If I upload the original image (going back to 4368x2912px @ 240ppi) and offer a 30x20" print, to stick witht he same example. If someone were to try to purchase that print, there is a message displayed saying that there is insufficient resolution.
 
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