Ratios/Cropping

Hi All,

I'm still looking into selling prints of my photos.

However, I'm getting confused with the ratio etc.

For instance, The image is 3624x2416 which is a size of 1.5:1 (3:2)
So, does this means I should only choose canvas or prints that have the same ratio?
Such as, 30.5 cm x 20.3 cm (which is 1.5) instead of 40.6cm x 30.5cm which is 1.33?

Also, my images seem to be at 72dpi, I have read that it should be at least 300dpi. However, if I change these settings in Photoshop CS it increases the file size tremendously as well as the image size.

Any advice would be great,
Thank you.

You can always crop the photo to achieve other ratios. You don't want to simply resize to the other ratios because that will result in the image being compressed in one direction or the other.

As far as DPI is concerned, when you change to 300 or 360, you will also need to change the size. Make sure constrain proportions and resample image is checked when you do this.

Thanks for the advice.

When I make sure those two options are checked, I change the DPI from 72 to 300 and it makes the file size over 400mb and puts the image to over 10,000+pixels in either direction... this is surely too large?

Amnesia180 wrote in post #12057540
Thanks for the advice.

When I make sure those two options are checked, I change the DPI from 72 to 300 and it makes the file size over 400mb and puts the image to over 10,000+pixels in either direction... this is surely too large?

DPI is irrelevant. In most cases you can ignore it.

That being said, most commercial print services print at 300 dpi. If you are just totally a "fingers in everything" type, you can resize to 1200 x 1800 at 300 dpi for a 4 x 6, or to 2400 x 3600 at 300 dpi for an 8 x 12, or to 3600 x 5400 for a 12 x 18 and so on. (Does the arithmetic make sense there?)

That being said, virtually every print service will reinterpolate to whatever size you want, IF the ratio is right. If it isn't right, then they still reinterpolate, but they will make ugly crops in the worst possible place.

Because they reinterpolate for you, that is why it doesn't matter.

Rad

(An exception would be printing to a specific size when the size you want is defined by the size of the image. With my IPF-6100 wide format printer, I do define the actual dimentions of the image in inches.)

1. Uncheck the Resample box.
2. That number 72 is nothing more than a nominal place filler that the Exif standard requires. Dpi (or more properly ppi) means pixels per inch. The only things that have inches are prints, in other words until you make a print there can't be a real ppi. If you have a 2000 x 3000 pixel image and make a 5x7.5 inch print, you are making it at 400 ppi. If you make a 10x15 inch print you are making it at 200 dpi. For best quality the pixel/inch relationship should be 300 ppi (which for your camera is, because 2416/300 = 8, an 8x12 inch print). However, as long as the ratio doesn't drop below around 180 ppi (a 13.3x20 inch print) the quality will be acceptable because in the print lab they will resample your image to the optimum for their machine (usually 300 pp).

Amnesia180 wrote in post #12057540
Thanks for the advice.

When I make sure those two options are checked, I change the DPI from 72 to 300 and it makes the file size over 400mb and puts the image to over 10,000+pixels in either direction... this is surely too large?

Let me try to put this another way, to explain what you are doing.

You say your image is 3624 x 2416. It is also 72 dots per inch. Simple math puts that as a "native size" of 50.3 inches x 33.5 inches. (3624 x 2416 divided by 72 dots in each inch.) Or put even another way, you know the edge that is 3624 pixels long? Imagine you start counting pixels. Every 72 pixels you move into the next inch. 3624 pixels is 50.3 inches.

Are you with me so far?

OK.

Now Photoshop has a picture that measures 50.3 inches by 33.5 inches. You then tell Photoshop that you want 300 pixels per inch, not 72. Well, then, Photoshop has to ask itself, "How many pixels, at 300 per inch, will I need to get to 50.3 inches?" The answer is 15,100 pixels along the long edge, and 10,050 on the short edge.

See, if you don't specify a size, it will keep the size (50.3 inches by 33.5 inches) that it thinks you want.

So, if you want to resize, enter a size, in inches as well as the DPI that you want. When you do that, you will get what you want.

Totally clear?

Rad

Thanks all for the great replies, this has made a lot more sense.

So essentially, with my image size of 3624x2416 as long as I don't go above 50.3inches x 33.5inches the print should still be OK?

I also need to make sure I have cropped my image to the ratio of the print required... i.e: 3:2 or 4:2 etc otherwise the print service will do that for me or stretch the image?

Thanks again! The ppi thing makes a lot more sense now.

Umm, hang on -- yes, crop to the needed aspect ratio, but you are thrown off by your image size. the 50.3x33.5 inch print size is being thrown way off by your misunderstanding of the ppi/dpi figure.

That figure has no real meaning until to translate it into "real meaning", and for your normal print a 50x33 inch print is not real, it's just using the 72ppi figure, which is really a bad print resolution.

It has been mentioned here that around a 180 ppi resolution or better will give a very good print. What that means is that an image will give a very good print quality at that resolution. You can actually print larger, as long as you view from a distance, but that range will help to where you can get closer.

So, get rid of the 72ppi/50x33 notion because it's just not real. You either send your image to the print shop at the "native" resolution and let the printer "translate" into its own "native" resolution, or you will want to use software to resize (and frequently sharpen) to give the print a "proper look" for a given size in inches at a given resolution which will not typically be anything like 50x33@72ppi.

I wrote above that you are safe with a 20D image at sizes up to 13 x 20 inches (180 ppi). That is for prints that will bear up to close inspection, but you can make larger prints that will look very good when viewed at normal viewing distances, which for framed and hung prints isn't with your nose two inches from them. I have made beautiful 20x28 (50x70 cm.) prints from a 20D sized image (from a 350D), but they were made by a good custom lab with a Durst Lambda printer that requires less up-resampling. However, the principle is that the bigger the print the further the viewing distance, so I'd guess that you could go up to 24x36.

Amnesia180 wrote in post #12060629
Thanks all for the great replies, this has made a lot more sense.

So essentially, with my image size of 3624x2416 as long as I don't go above 50.3inches x 33.5inches the print should still be OK?

I also need to make sure I have cropped my image to the ratio of the print required... i.e: 3:2 or 4:2 etc otherwise the print service will do that for me or stretch the image?

Thanks again! The ppi thing makes a lot more sense now.

Umm, to put it into really simple human terms, the pixels are your butter and the paper is your bread, the ppi value is a guide and does nothing more than tell you the extent to which you're spreading that butter.

What 3624x2416 tells me is that I can print the image anywhere from 360ppi and have a very high quality print that will be 10x6.7" or print it at 180ppi and have a good quality image that's 20x13.4"
The number of pixels remains the exact same amount in both cases, the only difference is that I told the printer to blow the image up across a larger area by spreading out the spacing of the pixels.

In any case, as was said before: "DPI is irrelevant. In most cases you can ignore it."

As for aspect ratio, that is very much a creative choice... If you want a professional look, never crop your works to fit a standard media, crop the media to fit the work, otherwise the framing will feel forced. Due to cameras, paper and frames having different sizes, something is bound to get cropped, but it shouldn't be your composition.

Kolor-Pikker wrote in post #12060874
In any case, as was said before: "DPI is irrelevant. In most cases you can ignore it."

It is good to be aware of some of the reasons to set the PPI in Photoshop. To change the DPI without changing the pixel count, resize the image but with resampling turned off.

1. When selecting View -> Print size. If Photoshop knows the the number of pixels per inch of your screen, it can display the file you are working on to match the print size in inches on the screen.

2. When using the inch rulers instead of pixel rulers to place items like text or other image elements on your picture at known locations, then the PPI needs to be set to make the rulers accurate.

3. When placing text, fonts are sized in points. There are 72 points per inch. The PPI needs to be set to match your final print in order to get text to be the desired size.

Good points, though people who use view print size, rulers and care about text size probably already know how to set up ppi; these settings are probably more important for design than photography. Additionally, in order for these to work properly, you also have to go into preferences and set up the screen resolution with the correct ppi as well.

Thank you for bearing with me all...

I think I'm slowly understanding this. So the DPI/PPI is (sort of) irrelevant. I do not need to change anything in Photoshop?

I am using Photobox Gallery for printing, will they take care of the print? And, assuming the aspect ratio of my images match the ratio of size of print, I can work out the DPI/PPI myself?

So, my image of 3624x2416 can be printed comfortably on an 18x12inch canvass? (Which tells me the image will be 201 PPI). If, for instance, the same image was only 906x604, the maximum I should look to print (for quality purposes) would be around the 6x4 inch postcard type size.

They are just examples, I would be unlikely to go that small anyway.

Bottom line, the larger (in pixel size, not file/MB size) I keep my image the better?

Providing I am now understanding the above...

How does this affect the printing service I am choosing to use? I do not think Photobox are specialist enough to review my images and choose the best cropping should my media fall into a different ratio. I.e: If I choose any canvass/post print size, I wouldn't want to offer a print of ratio 4:2 when my image is 3:2 as there will either be a lot of cropping or they'll just "spread" my image over it, causing the picture to look distorted and obviously unhappy customers.

You are starting to get a handle on it.

You get optimal print quality when your image is, say, 300 ppi, meaning an 8x12 print could be around 2400x3600 pixels. This is a "ballpark figure", because print services will take a larger or smaller pixel count and resample the image, but the amount of image data is there to give a good, detailed print.

You could think of a high quality 4x6 at 300 ppi as a resolution of 1200x1800 pixels.

Again, this is "ballpark". And for smaller prints, you can freely send larger files.

But, something to consider when you are preparing to print is "output sharpening" -- some people prepare a print by resizing a file to the wanted dimensions and then sharpening. This means you either "shrink" the file for a smaller print or enlarge it, so you create pixels to fill a large printsize and sharpen it although you don't add any detail. This happens all the time so you may have a 2400x3600 image that would make a high-quality 8x12 but you want to have a 16x24 print with a high degree of control so you could resample that image to 16x24@300ppi if you wanted and then sharpen it. Of course this would make for a huge file and many don't take that step but some do.

As to the aspect ratio, it's up to you to decide what to print at and prepare the image accordingly before doing all the other. For an 8x10 a fair amount gets cropped off an, IMO, it's wise to do this yourself before sending the file off rather than trusting the print lab to do it for you.

Great, I think I am getting there. (Thanks again for the further explanation too).

I think I've got it boiled down to making sure I have already edited/cropped the image to fit the print ratio of the image I'm supplying rather than relying on the print lab. Rather than creating 2, 3 or even 4 variations of the same photo, I think I would rather choose the one ratio to make my photo and choose products/print sizes to match that.

I think once I start getting the hang of editing images, I may then look at resizing the image to the actual size of print at a given ppi. But only once I've started getting better at this