How do I check the DPI of an image for specifically A3 landscape print?

[Chris P. Bacon]

More specifically, I should check the print DPI for an A3 crop of the image.

[TheDigitalDog]

In Photoshop, several ways to check what's currently set. Try Image Size for one, or you can set up this info to show in your Info Palette if you select the option. 

Does it matter; not really, no. This is simply a metadata tag. The number of pixels is key! 1000x1000 pixels at 300 dpi, 1000 dpi or 72 dpi is the same. It's 1000x1000 pixels. 

More here (an old but still valid primer):
http://digitaldog.net/files/Resolution.pdf

[Mylenium]

The DPI setting is part of the document properties and can be viewed in the file info or seen in the image resize dialog for instance. If you just cropped it from a larger image that had already correct values, that info doesn't change.

Mylenium 

[Chris P. Bacon]

I am asking for DPI not for PPI and DPI is calculated for print area.

How do I see in Photoshop what will the DPI be if I crop my image to A3?

The DPI is not visible, not in the Info panel, nor in the file info section or document properties.

There is no "DPI" shown in the screenshots you sent.

[TheDigitalDog]

DPI and PPI are used interchangeably to some degree. In Photoshop, which works only with pixels, it's PPI. A product that makes or uses dots would be DPI. 

300 PPI in Photoshop could be output to 300 DPI. Or not. But in Photoshop, it defines a "Size" using pixels; it is a pixel editor. 

[Chris P. Bacon]

But the dot size of printers and the pixel size of screens can be very different, so I cannot rely on that.

[TheDigitalDog]

But the dot size of printers and the pixel size of screens can be very different, so I cannot rely on that.

By @Chris P. Bacon

Yes you can. 

300 pixels (300 PPI) sent to any device that outputs 300 DPI will produce 1 inch. 

[jane-e]

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@TheDigitalDog wrote:

300 pixels (300 PPI) sent to any device that outputs 300 DPI will produce 1 inch. 

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Which printers do you recommend that output to 300 dpi these days, Andrew?

I just did a Google search and all that came up were label printers. The last time I bought a printer with only 300 dpi was in 1989 when most printers were 72 dpi. It could simulate to 600. What am I missing?

Jane

[TheDigitalDog]

 What am I missing?

By @jane-e

You can send 300 PPI to an Epson Ink Jet like my P800 or 3880 Jane. Or 240 PPI  or 72 PPI (which I wouldn't recommend). And you can have all produce 1 inch from that (or not). That such a printer doesn't use one image pixel to create one dot is kind of moot. It's using a kind of stochastic printing. 

My Canon Laser printer will print one dot for one pixel and output 300 dots per inch; its output resolution can be set for that. 

[Chris P. Bacon]

It seems then that printers have a "device dot ratio" (even can be changed as you say?) like screens have device pixel ratio?

[TheDigitalDog]

It seems then that printers have a "device dot ratio" (even can be changed as you say?) like screens have device pixel ratio?

By @Chris P. Bacon

Kind of, yes. The point is there isn't a one-pixel-per-dot relationship. And it really doesn't matter. 

Digital images don't have a size other than the space they take up on a drive. 

1000x1000 pixels is the same with whatever metadata tag is used for the possible output size! 

Again, the 1000x1000 at 1000 dpi (PPI) metadata tag is the same as if it had a 100 PPI tag. It is 1000x1000. 

The metadata tag at the time can tell you what could be output from those pixels, but that doesn't have to be the case. 

Play around in Photoshop's Image Size dialog after reading the resolution primer. You can alter the 'size' without increasing the pixels; no interpolation (adding or removing those 1000x1000 pixels). A printer driver may, repeat may, look at this number of pixels and the resulting size with this tag and just make a print that size. Or the user can force the issue in the driver, effectively altering the number of pixels used for each inch (or any other unit) for output. Until that takes place, there is no real size! There is a number of pixels and a tag, and the tag and or the number of pixels one divides up into a unit of measurement, perhaps inches, takes place after Photoshop; in the print driver. Or even a display. 

[Chris P. Bacon]

Does this mean that if I make sure that at the image dimensions in Photoshop there's at least 300 defined as "image resolution" it will be a quality print when exported or placed into Illustrator or InDesign? (It will be sent to print from InDesign).

[TheDigitalDog]

Does this mean that if I make sure that at the image dimensions in Photoshop there's at least 300 defined as "image resolution" it will be a quality print when exported or places into Illustrator or InDesign?

By @Chris P. Bacon

Not at all. There is nothing special or unique about 300 (PPI or DPI). It depends on the output device (and the viewing distance one would look at the print). High-quality photo quality inkjet? Billboard? 

Again, work in pixels! Again, the resolution primer provided explains all that. 

[Chris P. Bacon]

I asked this question because I want to determine the minimal image quality for print necessary specifically for A4, A3, A5, A6 and A7 sizes.

Okay, I acknowledged that the pixel count matters, apart from the print size.

Probably they use PPI in the apps instead of pixel dimensions in order to avoid confusions about aspect ratio.

So does this mean that the minimal image quality for print, for each size, can be stated in either pixel count and in PPI?

I would pick pixel count then, to avoid confusions.

I need to make a calculation for width pixel count only, since my aspect ratios are defined, to make it easier.

Apps should not use PPI as a print quality guide, because PPI means strictly screen resolution, not print resolution or print quality:

"Pixels per inch (ppi) and pixels per centimetre (ppcm or pixels/cm) are measurements of the pixel density of an electronic image device, such as a computer monitor or television display, or image digitizing device such as a camera or image scanner."

So it has nothing to do with the print quality of my image.

I need to find or make a pixel count per print area chart, totally skipping over the PPI.

Any advice where to find one or how to make one?

I think print area is easy to define in Photoshop if you place the image on a document with a predefined size, right?

Can Photoshop add fictional/predicted detail when digitally upsampling an image, to reach the desired print quality if the original image doesn't have the necessary pixel count?

Because if no detail is added, only the pixel count is increased, then the print quality will not increase by digital upsampling.

I make magazines, so the view distance is the same for me.

Theoretically Photoshop could create an image with 4 times the pixel count of the original image without adding any detail to the image, just by showing 1 pixel as 4. 

But I guess that wouldn't increase the print quality for the same area.

So does this mean that in the end not even the pixel count that matters, but the detail?

[D Fosse]

There's a fair bit of noise level in this thread, but you have been given correct answers. But you still struggle to understand the basic simplicity in this. It's very straightforward.

Ppi is no mystery, it means exactly what it says: pixels per inch. It's a standard equation: ppi = pixels/inches. Like any equation, you can determine any one of these if you know the other two.

Following that, printing A3 at a density of 300 ppi requires 4961 x 3508 pixels.

Printing at 220 ppi requires 3638 x 2573 pixels.

That's it. That's all there is to it.

DPI, as a printer parameter, is basically outside the scope of this discussion. While it can affect the final quality in its own right, it's not what we're discussing here, and it's not something you need to consider when preparing the file. It comes later at the printing stage. As has been pointed out, ppi and dpi are two different things that do not need to match and usually don't.

[Chris P. Bacon]

Ah, so even though PPI by definition is pixel by screen inch, you say that it can be used to calculate image print quality as pixel by print inch. I have never seen such a chart, I am looking.

If that's true, it means that printer manufacturers adopted this for their printers, otherwise I don't see how this could be so interchangeable.

[D Fosse]

There's no need for a chart. Just use Image Size in Photoshop (but it helps to understand the basic concept).

Involving screen pixels is also a red herring here. Ppi is a print parameter. Ppi defines a pixel grid on paper, the pixel density. This does not apply on screen, because a computer display already has a defined pixel grid. Screen ppi is whatever the display manufacturer made it to be. It's already given, so a ppi number on top of that makes no sense.

[Chris P. Bacon]

The Wikipedia article of PPI thinks otherwise, it says that PPI is specific to screens and scanners (and I would add maybe even to projectors).

According to Wikipedia PPI is pixel density. There are no pixels in print.

[davescm]

'The Wikipedia article of PPI thinks otherwise, it says that PPI is specific to screens and scanners (and I would add maybe even to projectors).'

You are misreading both the Wikipedia article and the information given in this thread. The pixel density of a screen is fixed and cannot be altered. So if screen A has a pixel density of 109ppi and screen B has a screen density of 240ppi then an image displayed with the same number of pixels will have a different physical size on each of those screens. The screen with the higher pixel density will display the image smaller on screen. The ppi data stored in the image metadata has no bearing whatsoever in that display size and is not used at all for on screen display.

A printer does not have a fixed ppi (it does have fixed values of dpi which are the dots that will be used to print the pixels).  So a print driver is sent pixels and has to be told how big to make those pixels on the paper. Note again, pixels not dots. That is what the ppi metadata in the image is used for. It tells the printer how many image pixels to print in one inch of paper. The printer then uses its dots to print out pixels at the density set by the ppi value sent along with the image pixels. Hence the ppi metadata used in Photoshop and InDesign is used to tell the printer how to convert pixels into a physical size on paper.

Dave

[davescm]

'Apps should not use PPI as a print quality guide, because PPI means strictly screen resolution, not print resolution or print quality'

No that is not correct. When displaying an image on a screen ppi is ignored altogether and the pixels are sent to the screen and displayed at whatever pixel density the screen uses. That is why the image viewed at a 1:1 image : screen pixel ratio will be a different physical size on different screens.

For print ppi does matter. It is ppi (not dpi) that decides the physical size of the image on paper when converted from pixels to a print area.  As stated several times above dpi is the dots that the printer uses to make up the pixels and is not used in the conversion from pixels to image size.

There is a formula that you can use to determine the appropraite ppi for viewing distance which is

ppi = 6878/Viewing distance in inches. However that is more useful for avoiding excessive pixels in large prints.

For magazine print that is to be printed commercially - talk to your printer who should be able to advise ppi required based on their press.

If you are printing yourself, then use 300ppi for most inkjets (there is a technical argument for 360 ppi on Epson print drivers to avoid internal scaling but on photographic images you are unlikely to be able to tell the difference). For laser printers use 300ppi for photos and 600ppi if the printer supports it for rasterised vectors.

Dave

[Test Screen Name]

"So does this mean that the minimal image quality for print, for each size, can be stated in either pixel count and in PPI?" What matters (what you can take home from the rather overwhelming set of replies here) is EFFECTIVE PPI. If you know what we MEAN by effective, that's great: you can calculate it. If not, you can just use InDesign to check the effective ppi for EACH image. This is not a value you can directly set in Photoshop! But depends on your scaling in InDesign.

"

"Pixels per inch (ppi) and pixels per centimetre (ppcm or pixels/cm) are measurements of the pixel density of an electronic image device, such as a computer monitor or television display, or image digitizing device such as a camera or image scanner."

So it has nothing to do with the print quality of my image.

"Pixels per inch (ppi) and pixels per centimetre (ppcm or pixels/cm) are measurements of the pixel density of an electronic image device, such as a computer monitor or television display, or image digitizing device such as a camera or image scanner." So it has nothing to do with the print quality of my image." No, that's not right, or is out of context. Effective ppi has EVERYTHING to do with the quality of your image. 

"Because if no detail is added, only the pixel count is increased, then the print quality will not increase by digital upsampling." You are exactly right. Many people want Photoshop to do some magic to fix images that aren't good enough to print. Now, Photoshop does have some guessing stuff in recent releases, which might do a better job than the printer, but I wouldn't personally use it. 

"I make magazines," Your printer (person, not machine) can tell you what effective ppi to use in your images, for the specific press, paper and ink you are paying for for. There isn't a universal number. 300 ppi is not universal, it's just good enough for most printing purposes.

[jane-e]

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@Chris P. Bacon wrote:

...will be a quality print when exported or placed into Illustrator or InDesign? (It will be sent to print from InDesign).

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Did you read my earlier post about Actual PPI and Effective PPI in InDesign? The Effective PPI is the one that matters.

Jane

[Chris P. Bacon]

Yes, but you can see that in this thread some people tell me to check the effective PPI, some tell to check the pixel count becuse that is what matters. If there is a correlation between the two in terms of print quality (I don't need the document size feature of InDesign in PhotoShop because I know my print dimensions in A3, A4, etc, so I can calculate the pixel dimensions necessary for quality print based on that, as @D Fosse pointed it out. Now I wonder which of the 2 should I use.

@Test Screen Name  said that I cannot check for ppi in relation to print size in Photoshop .(Not even if I define a document size and place the image on it? Photoshop doesn't assume that the document size will be the print size, as InDesign does, I suppose.)

So if I cannot check the print quality in Photoshop (for my specific print size) then I will always place the image in InDesign to check the effective PPI, but I could just check the pixel dimensions in Photoshop, since I can pre-calculate a chart based on what @Test Screen Name said.

[Chris P. Bacon]

I will print photos on A3 spreads.

That means that according to this thread, the quality threshold is a fixed PPI that is calculated specifically for the A3 size?

So if I set minimum 300 as "Resolution" at the image dimensions in Photoshop, will that guarantee the same quality image on A4, A3 and A2?

I don't think so.

I think I must find the minimum PPI for quality prints specifically for A3 print size.

But I can type 300 in the "Resolution" field at the dimensions no matter how many megapixels were the camera's capacity, right?

That means that 300 PPI is not a guarantee for quality print, even if the print size is a fixed A3, because it will depend on the initial megapixels capacity of the camera that the picture was originally taken with, is that right?

[Lumigraphics]

DPI is determined by the printer driver. There are no dots on the computer, there are pixels.