need help to re size to 300 dpi

[Wessex Wildlife]

I want to make sure that I am doing the right thing when I am asked to provide an image for print.

When asked for an image at 300 dpi I have to re-size because my Canon 7D camera produces files at 240. What I am doing is resizing (using Photoshop via CC) to 300 ppi. What's the practical difference between dpi and ppi?

Is there a reliable work flow technique for resizing images to 300 dpi and print-ready?

Can I set up my Canon 7D to produce print-ready images?

Is there as "best" colour space?

[IzzieK]

If you are using a PC, the shortcut is to hold down Ctrl and Alt Key + I. Then you can change your resolution. Is this what you are looking for?

[davidedric]

A couple of things.

Images don't have either a dpi or a ppi until they are printed or displayed, respectively. Can you explain more about your 7D producing a particular resolution?

How you resize for printing will depend on the software you are using, what is it, in your case? (There is also a debate running somewhere about whether there is a need to resize at all.)

If you can provide a bit more information about what you need to do, I am sure the folks here will be able to help out.

Dave

[Manfred M]

DPI = Dots per Inch and is related to displaying your image on screen. This information is only relevent if you are planning to display your image on a screen at full size. Your computer will automatically take care of scaling issues, and the only real reason for changing this dimension would be to guide output sharpening. Check your screen display's resolution (my default is 1920 x 1280) and the actual screen width (or height). If my screen is 24" across, then 1920 / 24 = 80 dpi.

If you are planning to post on a website using a browser, I tend to use the traditional 72 dpi because of variability of screens and browsers that people who will be viewing your images will use.

DPI = Dots Per Inch and is only relevent when printing. Here it is important to know the native resoilution of the printer you are using (this data can be difficult to find). HP and Canon photo printers use a native resolution of 300 DPI, while Epson photo printers run at 360 dpi.

Again, this can be somewhat academic, as the printers themselves use fairly sophisticated software to upscale of downscale an image. Some sources suggest that working at a even ratio of the printer's resolution will give you the sharpest image, but frankly I have not seen any difference in my work.

[ajohnw]

If you are planning to post on a website using a browser, I tend to use the traditional 72 dpi because of variability of screens and browsers that people who will be viewing your images will use.

Does that actually make any difference on a screen Manfred? The GIMP allows me to adjust the print resolution that the camera puts in the file but that doesn't change how the image appears on the screen at all. What does seem to matter for some usages is to set the actual screen resolution in applications. That way an A4 sheet etc will come out the correct size.

John
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[Mike Buckley]

David,

You are already in excellent hands so I will only caution you to be aware that the subjects of dpi and ppi that you brought up are very often inaccurately discussed on the Internet. People who post information about it so often think they understand it when they don't. Though that's understandable, it also leads to increased confusion and inaccuracy.

Manfred's post might be the most concise explanation of the facts and practical information pertaining to dpi and ppi that I can remember seeing. In fact, I'm seriously considering printing it and storing it in my camera bag so it's readily available the next time somebody starts discussing this stuff in person. I would be able to simply pull it out of the bag, hand it to them, and explain that that's my contribution to the discussion.

[DanK]

Manfred's posting is a very good, concise explanation. All I would add would be to go back to your writing that:

my Canon 7D camera produces files at 240

Your camera produces either a raw file or a jpeg, depending on the setting. You have a choice of several file sizes for each. Any of these choices produces a file with a given number of pixels in each dimension. "Inches" don't come into play, so DPI and PPI aren't relevant. So, as Dave wrote:

Images don't have either a dpi or a ppi until they are printed or displayed

So, I am guessing that the 240 is a number that appears in your software somewhere. For example, Lightroom will default to 240 PPI in its print module. This has nothing to do with the file the camera produced; it is just the software author's notion of a reasonable default for many printers. I routinely change this to 300 as I use a Canon printer, but to be honest, i don't notice the difference when I forget to make the change.

You started by asking:

I want to make sure that I am doing the right thing when I am asked to provide an image for print.

That all depends on who is doing the asking. If you mean that the software is asking, set the PPI to match the printer's recommendation. If you are sending it to a lab, you can forget about this. For example, I print most of my own, but I send a modest number of images to a US lab, Bay Photo. Their instructions are to send them the largest jpeg I can and let them worry about the rest. Just check with your lab for their preferences.

Dan

[Manfred M]

Does that actually make any difference on a screen Manfred? The GIMP allows me to adjust the print resolution that the camera puts in the file but that doesn't change how the image appears on the screen at all. What does seem to matter for some usages is to set the actual screen resolution in applications. That way an A4 sheet etc will come out the correct size.

John
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I don't think there is any noticeable difference outside of sharpening impact that I've noticed; and here "close enough" seems to work (i.e. resize to an appropriate height and width and sharpen at 100% and don't worry about the ppi). I find that chosing sRGB colour rather than using AdobeRGB or ProPhoto is actually more noticeable on screen when using a web browser.

[Geoff F]

David, some printing companies do ask for images at 300 ppi but there is little reason for this; although I suppose there is justification in requiring some average figure to prevent excesses in either direction.

But in reality, there isn't usually any difference in a print between 200 ppi or 300 ppi. I normally work at 240 ppi for my photos. This is set by my editing software as the default setting, but can be changed.

At one time it was recommended to use a figure which can easily be divided without producing half then quarter then eights of a pixel. And 240 is a good figure which gives 4 divisions before getting into fractions.

But with modern software this isn't an issue.

I usually do all my printing from 240 ppi images. I never see any point in upsizing an image, which means adding extra pixels just to reach a theoretical magic number.

In fact I can't see any point in asking for 300 ppi then saying that the image must be in a format like Jpeg which loses quality instead of Tiff or Psd etc which doesn't have any loss. I would much sooner use one of those even if I was printing at 200 ppi or a little less.

When resizing I simply go into the Image Size option (which will vary between programmes) set the resolution then enter the required size. In many cases I actually work in pixels not inches or millimeters etc.

For example, when uploading to the internet (eg CinC) I normally use 1000 pixels at 96 ppi (96 is the resolution which is standard for European monitors).

Resizing can get slightly more complicated when working on exact European paper sizes. Obviously a 3 x 2 ratio photo won't fit exactly on A4 paper (8 1/4 ins x 11 3/4 ins) so sometimes you do need to do a bit of careful resizing and cropping. Particularly if you need to fit a specific frame size with an equal all round border.

Which is where using a pre cut border mat can be useful.

You mention best colour space. Well there is always debate over this, but the 'safest' option is sRGB which is acceptable everywhere including the internet.

Some people insist that alternatives like Adobe RGB or others will produce a greater range of colour. While this is true, it doesn't normally make much difference for average photos when used under average conditions. And Adobe RGB needs to be converted to sRGB (or suitable alternatives) before uploading to the web.

[Dave Humphries]

Hi Manfred,

Normally I find myself in complete agreement with your posts, unfortunately this time, I fear some bits of your helpful (and well received) post may add to confusion among some readers.

DPI = Dots per Inch and is related to displaying your image on screen.

I think this first section was meant to be "PPI = Pixels per inch", as referring to a screen, especially as the second section also says DPI. That said, most people (myself included) use them interchangeably anyway, other than the "D" or the "P", it generally makes little difference (but should).

If I ruled the world; "DPI" would be used solely for the dots/inch that inkjet printers squirt on to paper - and that's usually measured in thousands. Everything else would be "PPI", because it is pixels we are talking about as there is no constant physical dimension involved. But I digress.

This information is only relevent if you are planning to display your image on a screen at full size. Your computer will automatically take care of scaling issues, and the only real reason for changing this dimension would be to guide output sharpening.

For display of a finished image, they really should be displayed at full size (meaning 100%), especially those published on the internet, which must be downsized so they fit most people's screens - and yes, output sharpened afterwards. Letting the computer (browser) handle it is what softens images.

One rare exception to this would be a stitched panorama, where, with the height at 1000px, the image might be 6000 or more pixels wide and allow viewers to scan across it marvelling at the sharpness

Of course, it also doesn't apply when you are editing an image or 'pixel peeping' previews for culling, etc.

Check your screen display's resolution (my default is 1920 x 1280) and the actual screen width (or height). If my screen is 24" across, then 1920 / 24 = 80 dpi.

I see this as completely irrelevant I'm afraid, all this does is work out your screen's ppi/dpi.
Assuming the 24" was the width and not the diagonal measurement usually specified.

Setting such a figure as an image's ppi/dpi figure is not going to make a jot of difference when viewed on a screen, it will go by pixel dimensional size alone and if too big, may well be scaled to fit. The really important thing is to ensure that, whatever orientation it is (portrait/vertical or landscape/horizontal), the height is no more than 1000px and the width no more than say, 1600px, so that it fits within the majority of modern LCD screens - when viewed in the browser's "F11"/full screen mode, I hasten to add.

One exception to this rule is when you are sizing to make a computer 'wallpaper' or screensaver - in this case you do want it to fit to the screen dimension - be that your screen dimension - or, via different size files, when producing them 'commercially'.

If you are planning to post on a website using a browser, I tend to use the traditional 72 dpi because of variability of screens and browsers that people who will be viewing your images will use.

The pixel dimensions of a web image are all that matters - so, my general advice is - switch the resize 'units' to pixels (NOT inches or cm), because this hides the dpi box, then size to never more than 1000 tall and if that criteria is met, typically no more than 1600px wide (but height is more important). then do the output sharpen with USM: 80-100%, 0.3px radius, 0 or 1 threshold.

Failure to observe these 'Dave guidelines' results in viewers being able to see:
a) the whole composition of an image (but it is usually soft)
OR
b) the image at best sharpness (but only part of the composition)

Please do clarify/correct me if I have misunderstood any of your points Manfred.


I apologise to the OP (Wessex Wildlife/David) for going a bit off-topic.
As I don't print, I ought to leave someone else to answer the original questions.

My technical observation would be it depends what size you are asking it to be printed at, as to whether setting for 300 dpi will result in an upsizing or downsizing of pixel dimensions to achieve what they want. Personally, I would find a lab/printer that understands that any such resizing is likely to have some adverse effect - especially if I didn't want a particularly big print, say 6 x 4 inches, why reduce a 6000 x 4000 px image to 1800 x 1200 px - it just seems lunacy to me
I would just print the full size (6000 x 4000) image (after output sharpening*) - but perhaps I am wrong here?
I don't print enough, or have the inclination to use heaps of ink, to know any better.

* this would probably need to have quite a wide radius to be seen on such a small print!

I am now thinking it might be better to supply the requested dpi, down/up size for 300dpi and sharpen with a radius that looks good on screen at 100% = 1:1 pixels. It might be better than what I do now.

I can see some logic in divisible pixel ratios to avoid some resizing issues, but unless they are asking for a dpi which is divisible by the printer being used and not just the ubiquitous "300 dpi", that may 'backfire'.

Hope that's helpful,

[Manfred M]

Dave- thanks for catching my typo.

By the way, I agree with pretty well everything you've written; for me the interesting part is just where some of these "urban legends" of photography come from. Many are really historical artifacts that seem to have a life of their own, and my aim was more of a history lesson; for instance the 72 / 96 ppi. Those are artifacts from the NTSC / PAL standards on analogue equipment, yet they continue to impact things today.

That being said; it is completely correct to talk about "native resolution"; but these too have a lot of baggage, based on not understanding how and why they are there and how they could impact the final image (nicely said, they don't). The screen manufacturer builds screens that display three different colours and because they are physical entities they actually do have a native resolution. What people don't realize is that the actual colours we see are a combination of physical light sources that are dithered (or pulsed) and different levels of illumination and frequency to display the colours we see. A TN display is natively 6-bits per channel (6 bits each of red, green and blue = 18-bit); which gives us 262,144 distinct colours. These displays are marketed as 8-bit per channel (24-bit colour), which corresponds to the commonly quoted 16.8 million colours.

Similar issue with colour printers; and while the print heads are natively capable of printing 300 dpi (HP and Canon) and 360 dpi for Epson, they do with with a very limited colour set; basic prints use cyan, magenta, yellow and black cartridges; higher end printers had different shades of some these colours and multiple gray cartridges. They again claim to handle a very wide colour space, but do so by varying the put down of these colours and by varying the size of dots of ink that they put down.

Both post-processing software and printer software / drivers hide these native resolutions from us and the actual dpi / ppi is something the end user really needs not concern themselves with. That being said; the very first generation or two of inkjet printers were not nearly as sophisticated and this is where some of these concepts about printing in full ratios of native resolution came from.

DPI and PPI in the modern world are really an un-needed carryover that confuses users. They are really no more than scaling factors that determine image size. This is no different than working backwards and suggesting that we want a 200 x 400 pixel image or to print on A3 size paper (in those cases the PPI / DPI could be calculated, but who really cares?). Images are generally downsampled for screen viewing and depending on the pixel count of the camera and print size, are generally upsampled. Algorithms take care of those things for us, but by examining the image at 100% output size, we can apply sharpening to take care of the too much or too little sharpness introduced by the downsampling and unsampling process.

[Colin Southern]

I want to make sure that I am doing the right thing when I am asked to provide an image for print.

When asked for an image at 300 dpi I have to re-size because my Canon 7D camera produces files at 240. What I am doing is resizing (using Photoshop via CC) to 300 ppi. What's the practical difference between dpi and ppi?

Is there a reliable work flow technique for resizing images to 300 dpi and print-ready?

Can I set up my Canon 7D to produce print-ready images?

Is there as "best" colour space?

Oh boy. Sorry David, this one always creates a lot of "chatter".

Basically, files only have resolutions when they have a size assigned to them. If a file is 900 pixels wide and 600 pixels high then it's resolution would be 600PPI if the computer or printer was told that the image was 1.5 inches wide and 1 inch tall. On the other hand, if you said "sorry computer - I lied before - the image is actually 6 inches wide and 4 inches high then without changing any of the image data, hey-presto, the image is now 150 DPI.

So as you can see, PPI is just a number. Or more specifically, if you divide the number of pixels by that number, that's the size the print will be, but whether it comes out of the camera as 240 or 300 or any other number doesn't make any difference; it's just a starting point so that when you start adding text layers and the like it knows how big to make things like 12 point type (so editing programs may need to know what dimension you consider the image to be; it doesn't really care what it is, but it needs SOMETHING to base it's subsequent efforts on.

In the contexts of your print, printers are always asking for 300 ppi - and frankly, it's quite annoying because it's kind of a meaningless concept in a digital age. Some examples. If you have an image that's 6000 pixels wide and 4000 pixels high - and that needs to be printed as a 6 x 4 at 300 ppi then you'll need to down-sample it to be only 1800 pixels wide and 1200 pixels high - so you end up throwing away information. In contrast, if you needed to print a 36 x 24 inch print at 300 PPI then you'd need a file that was 10,800 pixels wide by 7200 pixels high - so you'd have to up-sample your image (which can't create information that wasn't there originally, so it really is a waste of time as well.

Bottom line is "don't worry about it until you need to send it to the printer, and at that stage, just crop it or up-sample it so that it's the required PPI AT THE REQUIRED SIZE. PPI is meaningless without an image size to go with it.

In terms of PPI -v- DPI, DPI is the physical dots laid down on the paper, regardless of the image pixel dimensions. eg My Epson 7800 prints at 1440 DPI regardless of whether the source image is 1 PPI or 1000 PPI - it simply up-scales the image as required. Inkjet printers are what make a complete mockery of the 300 PPI "requirement" ; if you down-sample an image and throw away data there's no benefit to the print. If you up-sample an image there's no benefit to the print either (because if you didn't do it to match it's native resolution then it does it automatically anyway), and you can't add information that wasn't captured in the first place.

If commercial printers (the people not the machines) understood any of this they'd simply make the changes to the image themselves -- it's trivial to do.

If you want to do this in PS CC, make a copy of the file first, then just go into IMAGE -> IMAGE SIZE, plug in the values you want for height, width, and resolution - MAKE SURE THE RESAMPLE BOX IS TICKED - and click OK. Job Done.

Can you change the default resolution from your 7D - no - probably not. Regardless, it's probably being assigned by the ACR RAW converter which you CAN change in the workflow options link at the very bottom in the middle, but as I've tried to explain, it's pretty much a meaningless concept.

"Colour spaces" is a bit of a loaded question I'm afraid; big spaces like ProPhoto won't clip any camera data, but may mean that you capture colours that you can't display accurately because they're outside the gamut of your monitor, which can lead to problems when you adjust those apparantly wrong colours and then wonder why they print funny (because they were actually right in the first place, you just couldn't see it).

Hope this helps

[Richard Lundberg]

<In terms of PPI -v- DPI, DPI is the physical dots laid down on the paper, regardless of the image pixel dimensions. eg My Epson 7800 prints at 1280 DPI regardless of whether the source image is 1 PPI or 1000 PPI - it simply up-scales the image as required. Inkjet printers are what make a complete mockery of the 300 PPI "requirement" ; >
No they don't. You don't understand what a high dpi inkjet does. The printer forms a cell of its very high dot numbers to perform like an image setter. This is what produces the color and tonal range. Google Epson for a while and you will begin to understand.

[Colin Southern]

No they don't. You don't understand what a high dpi inkjet does. The printer forms a cell of its very high dot numbers to perform like an image setter. This is what produces the color and tonal range. Google Epson for a while and you will begin to understand.

1440 is the native resolution it produces (2880 at highest/slowest setting).

Point I'm trying to make to the OP is that the source resolution isn't the issue that printer folk make out; if they're using inkjets then the print driver will re sample the image regardless, and it it's more conventional equipment then they can easily do it themselves.

Instead, they insist on this meaningless 300DPI mantra that has folks unnecessarily running around like headless chooks.

[Colin Southern]

To the OP,

In 50 words or less ...

- if you want to change the resolution and automatically accept a new size that an image would print at, go into Image, size - type in the required resolution - uncheck re sample, press OK.

- To specify both the resolution and printable size, go to the same place - fill in all 3 fields - check re sample - and click OK.

Note that images usually require output sharpening after being re sampled.

[jcuknz]

Deleted duplicate posting.

[jcuknz]

Now the computer has deleted my posting ... what the heck is going on?

Awayway, although interpolation is probably an obselete technique in these days of high Mp cameras it was a vital part of getting good pictures when using 3Mp and 5Mp cameras for A3 prints. I never did landscape but I guess the process wouldn't produce the detail expected with the computer inventing extra pixels based on those surrounding which resulted in some loss of resolution .... BUT if you shoot big and bold as I usually did being aware of my gear and its deficiencies it worked well.

The guts of my post which the computer lost was your camera doesn' work at 240 PPI but produces 5184x3456 pixels for you to throw away by cropping or divide iby the print size.
In the early days when I first struck this kind of thread I had three 5Mp cameras claiming to work at 72,180 and 300 dpi .... they were Canon Panasonic and Nikon so obviously the Nikon was the best camera .... it was ...
but for other reasons

[Wessex Wildlife]

ENOUGH! Wow! I am extremely grateful for the huge response. At first I thought that Mike Buckley's suggestion was a good one: I could print this out and then smugly hand it to anyone who started a discussion about image size. But as things progressed I realised this would never work, what if I dropped the print-out on the person's foot? It could break a toe!

Only kiddding, I really am very much in awe of your knowledge and convinced that some of you need to get out more. I now know what to do, thanks to Colin for a synopsis and to all the rest of you for the detail, divergences, context and commitment.
Dave Blake

[Colin Southern]

No worries Dave - hope we helped (somewhere!).