How do i resize for printing

[Rod Boughton]

Hi everyone, I would like some help please.
So far I have never printed any of my images, but now I would like to, but I don't know how to resize them after processing for the best quality for printing at large sizes.

I have a canon 600D which is 18mp, I use lightroom 3 for most of my editing, then finish off in CS6. By the time I have finished processing the images seem to have reduced in size, so can someone tell me how to save the images at their largest size for printing at good quality please.

Thanks in advance for your time and knowledge.

 

[droj]

By the time I have finished processing the images seem to have reduced in size, so can someone tell me how to save the images at their largest size for printing at good quality please.

Give more info about your exact workflow - such as settings. Do you mean reduced in file-size? In CS6 you can check the overall pixel dimensions - pixels per inch are distinct from this. It could be that your LR export settings need looking at.

 

[EOS_JD]

Rog is right. It's all about the number of pixels.

PPI controls the print size.

Print Size = Pixels/PPI
So if you have 3600 on the long edge you divide that by the print size you want (say 12")

that would be 3600/12 = 300ppi

 

[Pookeyhead]

By the time I have finished processing the images seem to have reduced in size,

There's no reason why this should be the case. What's making them smaller, and how much smaller are they once edited?


To size for print, just use Image Size in Photoshop. See below.

What the video doesn't show (forgot) is the resizing options... shown below.

For maximum quality when making images larger than native (setting 300 ppi with 'resample' unchecked) select preserve details. For making images smaller (as in my case in the video) use bicubic sharper.

 

[Pookeyhead]

Rog is right. It's all about the number of pixels.

PPI controls the print size.

Print Size = Pixels/PPI
So if you have 3600 on h elong edge you divide that by the print size you want (say 12")

that would be 3600/12 = 300ppi

The problem with this, is that sending a file away to be printed, the printer may have no clear idea as to what size you want it printed, as you're only setting a print resolution figure instead of resizing the image to print at a certain size/resolution. For instance, a file from my camera is 7360 across, so dividing that by 12 for a 12" print gives 613 ppi. Best to resize at 300ppi as this is the accepted print res for most commercial print outlets. It doesn't really matter that much, and yes, you can input a ppi figure with 'resample' unchecked so as not to alter the pixel resolution, but then the resizing will be handled by the printer, and that's a variable I'd rather not lose control over if someone else is doing the printing.

 

[EOS_JD]

The problem with this, is that sending a file away to be printed, the printer may have no clear idea as to what size you want it printed, as you're only setting a print resolution figure instead of resizing the image to print at a certain size/resolution. For instance, a file from my camera is 7360 across, so dividing that by 12 for a 12" print gives 613 ppi. Best to resize at 300ppi as this is the accepted print res for most commercial print outlets. It doesn't really matter that much, and yes, you can input a ppi figure with 'resample' unchecked so as not to alter the pixel resolution, but then the resizing will be handled by the printer, and that's a variable I'd rather not lose control over if someone else is doing the printing.

David
The complete opposite - PPI SETS THE PRINT SIZE for any given pixel resolution (nothing else)

For larger images I agree reducing the number of pixels to get to 300ppi makes sense. It can reduce file size dramatically and does inform the printer the size you want so long as you maintain the required number of pixels and proivides top notch quality (mainly because you have the required number of pixels).

But as you get larger prints and you don't have enough pixels for 300ppi you set the ppi for the exact print size you want - Nothing could be clearer. The instruction will already be clear from what you selected.

Lets say you have that same 3600 pixel image and you want a 30" print. Setting 120ppi tells the lab immediately you want a 30" print (3600/120 = 30")

Also you tell the lab you want 30" and you pay for a 30" print. The instruction is there and reinforced - you don't need to resize the image.

300DPI (not ppi) is the standard printer resolution and I think this is where people go wrong - They associate printer resolution with image resolution. You do not need 300ppi for your images to look great. And you will probably be damaging them (although to a very small degree) if you start adding computer generated pixels by photoshop.

In fact the larger you go the smaller the ppi value can be!

The lab will still print it at 300dpi (as that is normally their print machine resolution) but you can send the image at the correct ppi which sets the instruction on the actual size you want the print. In this case it would be printed at 120ppi (3600/30) Also telling the lab that the size is correct

I totally disagree that the 300ppi is a standard also. Some labs don't care some want odd numbers too but providing the correct resolution for the size of print you want will give the best results.

An example below......

You'd be surprised at the great quality of prints at very low ppi values.
http://help.smugmug.com/customer/po...on-requirements-for-printing-through-smugmug-

 

[arad85]

David
The complete opposite - PPI SETS THE PRINT SIZE for any given pixel resolution (nothing else)

PPI sets the number of pixels that are printed in 1 inch if the printer actually takes any notice of it

The (very) few times I have had stuff printed, I resize the image to my print shop's DPI x no inches I want the image and then get them to print it 1:1. If you don't do this, you are leaving the resize and any post processing to the printers. It's one way to do it, but I'd far rather get a print back that I've sized myself. I know what's been done to it then.

I think that is all David is saying too...

 

[EOS_JD]

PPI sets the number of pixels that are printed in 1 inch if the printer actually takes any notice of it

Absolutele correct. But it's a linear figure. In one inch of print there are 300x300 dots.

So if you have 3000 x 2400 pixels and printing with 300 in each inch (300ppi) it's 10" long x 8" wide (3000/300 and 2400/300)

If you change the ppi to 200ppi you now have 3000/200 = 15" x 2400/200 = 12"

That's how it works. PPI ONLY CHANGES THE PRINT SIZE. So long as the pixel resolution of the documement remains the same PPI does only one thing.

Px = Print Size x PPI
Print Size = Px/PPI
PPI = Px/rint size

(same very simple equation written three ways)

The (very) few times I have had stuff printed, I resize the image to my print shop's DPI x no inches I want the image and then get them to print it 1:1. If you don't do this, you are leaving the resize and any post processing to the printers. It's one way to do it, but I'd far rather get a print back that I've sized myself. I know what's been done to it then.

I think that is all David is saying too...

Firstly you cannpt resize "DPI"...... It's PPI. DPI is set by the print mnachine (think oin your home printer - it's the quality setting) ie how many drops (dots) of ink on the print itself.

The printer's RIP software will most probably do a far better job of any resampoling required. you do not need to print at one pixel to one dot? I ALWAYS size prints myself - Youy are not just resizing you are resampling the image which is very different and really you have no idea what is being done other than ;photoshop is generating pixels itself. By not resampling you know exactly what you have is the original detail in the image

How do you think billboards are printed? They don't create absolutely massive files...... They print at 10ppi

Here's a video explaining it too (using a large image).

I also need to do some more work to this blog post to make it more readable - But the gist of it is there.

http://www.jbdavies.co.uk/resolution/ppi-dpi/

 

[EOS_JD]

Diplicate post I think!

 

[EOS_JD]

PPI sets the number of pixels that are printed in 1 inch if the printer actually takes any notice of it

Just one further point.

The printer himself actually doesn't need to look at the ppi Value. It is not set by you or me - It's only set at the point the image is actually sent to the machine - it's not a fixed number. The ppi is only detmined at the point the image is sent to the printer. eg

Lets say you send a 3000x2400 image and you wanted it printed at 10x8 (you would send as a 10x8). That's fine. But lets say the printer sends that same image file to be printed at 15x12. In fact all he's doine is lower the number of pixels in each inch of the image (lowering the ppi to 200ppi).

So as you can see the ppi only changes the print size.

At home it's crucial for me to get the exact size of image I need on my papers and you can very accurately size prints with ppi.

 

[arad85]

Oh dear.

Did you actually read what I wrote?

Absolutele correct. But it's a linear figure. In one inch of print there are 300x300 dots.

No. 300dpi is common, but not the only value - some print at higher resolution, some lower.

That's how it works. PPI ONLY CHANGES THE PRINT SIZE.

if you know what the DPI of the printer is, you can predict the print size assuming the printer reads it. If the printer does not read your PPI, then you won't get the image size you are expecting.

Firstly you cannpt resize "DPI"......

I said you resize to the DPI of the print house. If they print at 300 dpi and you want a 10" print, the image I'd send them would be 3000 pixels with a ppi of 300. If they print at 250dpi, I will send them an image of 2500 pixels with 250ppi.

The printer's RIP software will most probably do a far better job of any resampoling required.

You may believe that, but I don't (whether it is true or not, I don't care, I don't believe it to be the case).

you do not need to print at one pixel to one dot?

I never said you did. I said I resized so that when I send it to the print house, they are printing 1 pixel -> 1 dot. That is my choice because then I do the processing to get to the image size I want, not the print house. As an aside, if you don't print at 1 pixel to 1 dot, then the printer will be resampling your image so that it knows what to print at each dot that it prints. See the point immediately above this one.

Youy are not just resizing you are resampling the image which is very different and really you have no idea what is being done other than ;photoshop is generating pixels itself. By not resampling you know exactly what you have is the original detail in the image

Umm. No. If you send a 300 x 200 pixel image to a printer to be printed at 20 pixels per inch on a printer that prints at 300 dpi, something somewhere needs to resample the image so that the printer can figure out what to place at each of its 300 print points per inch. If you don't size to the output DPI then something out of your control will take your image, resample it to the right size for the printer and then print it.

How do you think billboards are printed? They don't create absolutely massive files...... They print at 10ppi

The printer will be doing far higher than that so the pixels are resampled before they are printed. I prefer to do that myself rather than let someone else - who uses a resampler to get to their printers native resolution - do the job.

The problem is simple. If you are printing a 10" print on a printer that prints at 300 dpi, something, somewhere will take whatever image you provide it and resample it to 3000 pixels along that edge so the printer knows what to print at each of its 300 points per inch.

 

[EOS_JD]

Oh dear.

Did you actually read what I wrote?

Yes

And I then did some further research on printing and resampling and I have to admit I'm being swayed by some but then swayed back by others lol

But the dpi would still never have any effect on the size of the image you are printing - resampling as I am reading it will have an effect depending on how you do that.

No. 300dpi is common, but not the only value - some print at higher resolution, some lower.

Both 300ppi and 3000dpi are common but you don't need to resample to get the right size. However from further reasing it is advised to resample to the bnative value or a factor of that (like half). I need to do more research though as this is not something I've really read much about and thanks for highlighting it. Interesting

if you know what the DPI of the printer is, you can predict the print size assuming the printer reads it. If the printer does not read your PPI, then you won't get the image size you are expecting.

I would have thought all printers read the ppi. But niormally we stipulate the size we want (like 10x8) and many send the poriginal file with a ppi value not set by them.... But still get the 10x8 back - although may not be the best quality it could be.

The dpi though of the printer has absolutely NOTHING to do with the size of your prints. DPI is about how much ink you place rather than the size of the image.

I said you resize to the DPI of the print house. If they print at 300 dpi and you want a 10" print, the image I'd send them would be 3000 pixels with a ppi of 300. If they print at 250dpi, I will send them an image of 2500 pixels with 250ppi

I'm looking at this and can see the argument. Not 100% convinced yet but more reading needed I do still think the difference is tiny as I have had many great images printed at vbery low ppi values and always printed at the highest dpi the printer supports. Size was always based on the ppi.

You can easily test this at home. Set your printer on its maximum quality (maximum dpi). Take the same image and print it at a variety of ppi values. Do again at the next setting down on the printer. The print size will always relate the ppi and dpi (quality) setting will have zero effect on size. DPI however will have an effect on the quality of the image output no matterthe ppi of the image.

You may believe that, but I don't (whether it is true or not, I don't care, I don't believe it to be the case).

That's fair. I speak from experience but I rarely resample images. I send the pixels I have at a lower ppi to get larger images and get great results back! My 3m image in the opffice at 75ppi looks great (printed on a 300dpi printer). Perfect resize gets great reviews and althougyh I own it I've never felt the need to slow my whole process down as the results using pixels available have alwaysd been great.

QUOTE="arad85, post: 6634138, member: 20620"]
I never said you did. I said I resized so that when I send it to the print house, they are printing 1 pixel -> 1 dot. That is my choice because then I do the processing to get to the image size I want, not the print house. As an aside, if you don't print at 1 pixel to 1 dot, then the printer will be resampling your image so that it knows what to print at each dot that it prints. See the point immediately above this one.

I suppose we can argue which way is better and as I said in reality the difference is negligible either way - Which really supports why do it in the first place because all you do is increase file size, demands on your computer, slowing down the workflow and if uploading (especially a lot of images) it takes much longer.....

But I am interested in reading more on this so open top changing my mind lol

Umm. No. If you send a 300 x 200 pixel image to a printer to be printed at 20 pixels per inch on a printer that prints at 300 dpi, something somewhere needs to resample the image so that the printer can figure out what to place at each of its 300 print points per inch. If you don't size to the output DPI then something out of your control will take your image, resample it to the right size for the printer and then print it.

Is this resampling? Surely more dots are just placed on each pixel? I can see it being resampling if the ppi was higher than 300 though? Or am I getting that wrong?

The printer will be doing far higher than that so the pixels are resampled before they are printed. I prefer to do that myself rather than let someone else - who uses a resampler to get to their printers native resolution - do the job.

Really? I need to read more about this

The problem is simple. If you are printing a 10" print on a printer that prints at 300 dpi, something, somewhere will take whatever image you provide it and resample it to 3000 pixels along that edge so the printer knows what to print at each of its 300 points per inch.

This is what I don't get. Surely each pixel can have more than one dot without resampling? Again I need to look at this more Do you have any references?

 

[EOS_JD]

http://www.steves-digicams.com/knowledge-center/coming-to-terms-with-dpi-ppi-and-size.html

Even reading that I'm confused but I see the points

 

[Pookeyhead]

David
The complete opposite - PPI SETS THE PRINT SIZE for any given pixel resolution (nothing else)

I don't believe I suggested otherwise.

For larger images I agree reducing the number of pixels to get to 300ppi makes sense. It can reduce file size dramatically and does inform the printer the size you want so long as you maintain the required number of pixels and proivides top notch quality (mainly because you have the required number of pixels).

uhuh.. ditto...

But as you get larger prints and you don't have enough pixels for 300ppi you set the ppi for the exact print size you want - Nothing could be clearer. The instruction will already be clear from what you selected.



Lets say you have that same 3600 pixel image and you want a 30" print. Setting 120ppi tells the lab immediately you want a 30" print (3600/120 = 30")

Also you tell the lab you want 30" and you pay for a 30" print. The instruction is there and reinforced - you don't need to resize the image.

300DPI (not ppi) is the standard printer resolution and I think this is where people go wrong - They associate printer resolution with image resolution. You do not need 300ppi for your images to look great. And you will probably be damaging them (although to a very small degree) if you start adding computer generated pixels by photoshop.

While I agree with all of that, I have to disagree to a point. While you can't ADD what's not there, simply sending (for argument's sake) a 8MP image to a printer at 30" by setting 115ppi is not managing anything, and eventually you will see aliasing if you keep on going down this route. Aliasing is ugly... no one wants to see it. Careful resizing of the image, while adding nothing in the way of detail or resolution, can manage aliasing quite effectively.

Sorry... no one likes jaggies, and your method just dumps it to the printer as is, and when you're enlarging a digital image so much, that can look absolutely **** once you get into printing images from crap cameras really big. I can only assume by your answer that you don't do much printing for photography galleries then huh?

I have absolutely no hesitation in resizing images up in order to print, particularly exhibition prints that are often heavily scrutinised. Seeing aliasing is absolutely not going to cut it with exhibition prints I'm afraid... it's like some kind of cardinal sin... you just don't do it.

It's not unusual for people to want to over-print images, and expecting 40" prints from relatively low res equipment.

Here's a 8MP image... just the first one that came up by filtering for image size.

To print at 40" by your method, one simply sets 86ppi, and it will print at 40"... yes... no one's arguing with you here, least of all me. PPI sets print size... yeah...

however... look at that 40" print closely (which people actually DO despite all this crap about ideal viewing distances) you'll see this...

Now... carefully resize the image RESOLUTION to 40" at 300ppi using smooth gradient bicubic and sympathetic sharpness masking and you get this...

I know which I'd rather have hanging on my wall Jim. You've not added anything in terms of absolute detail... you can't add what's not there as I'm sure you know full well, but aesthetically, most would agree that the second one looks less "digital" and more pleasing due to the well managed anti-aliasing. Of course, once you step back a little you'll see no difference between them at all, but seeing pixels (aliasing) is not something anyone wants. There's no loss of detail... but there's less aliasing. THIS is what you want when upsizing a file for print. Viewed at "normal" distances there's no difference between the two - literally none (click here for 1:1 print preview - yes my screen size/resolution is calibrated in PS for accurate 1:1 mapping), but for the few pedantic idiots who stick their noses right up to your prints... why let them see ugly aliasing? With this in mind, I challenge you to find fault with my reasoning, and more importantly... my results.


Your knowledge is technically correct... no one's doubting you, but your printing methods are not.

Also... and this is really, really important Jim... the title of this thread is "How do I RESIZE for printing".


I'll let the readers decide which method they prefer. Carry on debating if you wish... but images are all that matter 'round here Too much talk to prove who knows the most in typical armchair warrior fashion... and not enough getting on with the job. Results matter... everything else is b******s.

Oh.... and Merry Christmas

 

[arad85]

This is what I don't get. Surely each pixel can have more than one dot without resampling? Again I need to look at this more Do you have any references?

I agree with David - you've basically got the dpi and ppi idea right but (there always is a but...) I don't think you are understanding how printing an image works at the low level and what resampling means.

A printer has a native resolution - typically, around 300 dpi. When it prints, the printer will print 300 dots per inch. It always prints 300 dpi, no matter what you give it. If you give the printer driver an image that is 300 x 200 pixels and ask it to print 10" in size along the long edge, it prints 10 dots per pixel, so you end up with a 3000 dot image on paper. Consider 2 pixels next to each other on the image, with values of 20 and 80. If you do dumb printing you get (on the paper):

20 20 20 20 20 20 20 20 20 20 80 80 80 80 80 80 80 80 80 80

which will be blocky - and is effectively what David has done in the first zoomed image above - so the printer driver may smooth it:

20 20 20 25 30 40 50 60 70 80 80 80 80 80 80 80 80 80 80 80

which will probably look pretty horrible or it could smooth the transition:

20 20 20 20 20 20 30 40 50 60 70 80 80 80 80 80 80 80 80 80

which will look better... or it could smooth it... well, you get the idea. There are an almost infinite number of ways the printer driver can take your 300 x 200 image and output it to dots on paper. If you don't match image resolution to print resolution, you are leaving this resampling (and yes, there is always resampling when you go from one resolution to another - and a printer dot is just a pixel in print speak) to the printer driver. Matching the image and print resolutions in PS or LR (or whatever your favourite processing program is) gives you control over that process. It may well be that the printer driver has as good or better resampler than LR or PS, but I'd personally not want to take the chance.

 

[Pookeyhead]

Matching the image and print resolutions in PS or LR (or whatever your favourite processing program is) gives you control over that process. It may well be that the printer driver has as good or better resampler than LR or PS, but I'd personally not want to take the chance.

Exactly. Besides... many printer drivers will do absolutely nothing in terms of aliasing. You set the document size by inputting a PPI figure, and if the printer doesn't NEED to do anything (which it wouldn't) then it just dumps it to the printer at the desired size.

 

[StewartR]

There's obviously some confusion here, mostly with @EOS_JD on one side of the communications breakdown and @Pookeyhead and @arad85 on the other side, and I think I can see where it might have come from.

It's the casual use of DPI and PPI interchangeably, as if they mean the same thing. Unfortunately this confusion isn't helped by the fact that a lot of software uses DPI when it should use PPI, which entrenches and institutionalises the confusion.

I'm sure (most of) you guys know (most of) this, but just for the benefit of others:

PPI is Pixels Per Inch and it's what matters when you're worrying about image quality. Almost always, anything that's said about image resolution is talking about PPI, even if the person doing the talking says DPI.

DPI is Dots Per Inch. Obviously if 1 Pixel = 1 Dot then there's no difference between DPI and PPI, and most of the time that's fine. But when you're printing, inkjet printers use multiple little dots of ink to create each pixel. (Obviously have to, or otherwise the number of colours they could reproduce would be limited to the number of different colours of ink they use.) So a printer might print at, say, 1200 DPI but only 300 PPI, and in simple terms that means each pixel is constructed from a 4x4 pattern of ink dots.

Does that help?

PS Here's an example from one of the posts which could have been confusing. @arad85 is equating 1 Dot = 1 Pixel, which ain't necessarily so:

The problem is simple. If you are printing a 10" print on a printer that prints at 300 dpi, something, somewhere will take whatever image you provide it and resample it to 3000 pixels along that edge so the printer knows what to print at each of its 300 points per inch.

 

[arad85]

There's obviously some confusion here, mostly with @EOS_JD on one side of the communications breakdown and @Pookeyhead and @arad85 on the other side

I don't think there is a comms breakdown - I understand perfectly what David & Jim are saying (and judging by his posts Jim is seeing what we have said too - but I'll leave that up to him to really confirm or deny ). And you are right - there are dots and there are dots! but the printer will always have a native pixel resolution (i.e. the smallest element that can be represented by the printer) and that's what I size for.

My concern is I believe the resampling of the image for printing is best done by the person sending the image to be printed, rather than by the person doing the printing. David and my "method" ensures just that. Jim's leaves it to the printer which works but as a confirmed control freak it worries the heck out of me

 

[EOS_JD]

I'm not convinced yet Andy but I do see what yopu are saying and wouyld like to have a trial at seeing what differences I can make by printing some samples (should be easy enough).
there's a variety of ways to resample too - And Ps is generally not the best although does a great job.

TBH for most of the work we do, the difference is tiny.

 

[Pookeyhead]

I'm not convinced yet Andy but I do see what yopu are saying and wouyld like to have a trial at seeing what differences I can make by printing some samples (should be easy enough).
there's a variety of ways to resample too - And Ps is generally not the best although does a great job.

TBH for most of the work we do, the difference is tiny.

Images don't lie (except perhaps in a narrative sense). I believe my examples should pretty much settle the argument.

 

[EOS_JD]

Prints don't lie I would agree

 

[Pookeyhead]

Prints don't lie I would agree

Then scan some prints that demonstrate that I'm wrong. Show us all.


Controlling the increase in image pixel resolution yourself to get a bigger print is always better than lowering the print resolution to force a bigger print. Fact... as demonstrated.

As I said... not faulting your knowledge... just your working methods.

 

[EOS_JD]

I like a good debate and always open to viewing things differently
Cheers