Printing and PPI

[allenlennon]

Hi all, most of my images are at 250PPI. And some are 300-350PPI. I read somewhere on CiC where 300PPI is a good benchmark for printing. And what i want to know, is there i easy calculations or an easy way of achieving this. I know it depends on what size i am going to print, and not all of them are going to be big, but i say the biggest i would print is a size of an A4 piece of paper. So is there a formula, chart or a guide to get the PPI right for the size of the print i want? Im asking because my sister is about to move in her new place, and wants to hang some of my photos up. And i want them looking the best it can on print. And she is unsure of what size she wants, and i told her that i wouldnt get any bigger than the size of an A4, cause A4 is the highest i would go with out lose of quality. Any help would be great!!!

[Andrew1]

The calculations depend on the size of the file. From there you determine what size of print you want and what the resultant ppi for the print is.

As an easy example if your file size is 7.2 meg with dimensions 3000 X 2400 you just divide. If you divide by 300 ppi you can get a print 10" X 8". If you want it a bit bigger then at 240 ppi you'll get a print 12.5" X 10". Simple. If you want a 5 X 7 at 300 then you'll need to downsize (or the print lab will) to 1500 X 2100. Where you set this and play with your sizes depends on what software you are using. Let us know and someone with the same software can give you specific directions.

[allenlennon]

So you divide the file size by the dimensions, for example(your example) 7.2/3000x2400? ThanDivide by 300PPI? And i use CS5. Sorry i am not a smart person Can you simplify that for me>??

[allenlennon]

Ok, i think i got most of it. you divid the dimensions by the PPI, like 3000x2400 you divided 3000/300PPI and 2400/300PPI wich gets me 10x8. I got that part, where does the file sizes come into it?

[Manfred M]

You don't really need a guide as your printer driver will take care of the interpolation to the printer's capabilities.

The display on a monitor process and the output by printer are totally different. A monitor is really quite similar to your camera's sensor in the way it interprets colour. Individual pixels of red, green and blue work together to illuminate each pixel from an off to a fully bright position to give you a full range from black to while.

A printer on the other hand either deposits a drop of ink or it does not. Less expensive printers have a single drop size and more expensive ones will deposit two or three different drop size per line. There is a similar issue with inks; less expensive printers work with four colours and more expensive ones will use double or even more colours. Different quality modes of the printer will vary the way the ink is deposited as well.

What this all means is that the print driver in Photoshop, Lightroom or whatever program you are using to print has to take the your image file and recalculate how it will output the image onto the paper, taking into account any settings or paper profiles and the printer you are using. A glossy paper is going to give you higher resolution than one of the more expensive "premium" textured papers.

I have not done a lot of testing, but have found that I feed the printer the highest resolution image I have and let it take care of the rest. The smaller the print, and you are doing fairly small prints, the less of a problem even low resolution files will be. It looks like your 250 ppi - 350 ppi will be more than adequate. Native output in RAW from my camera is 240 ppi.

[allenlennon]

thanks grumpy driver, but i must say that, im not printing on my printer, i can and have and produced great standard photo size for a album, and can go up to A4, but the price of ink(let alone how much ink it uses to print photos) is not exactly cheap, and i cant refill my cartridges, if i could i would print my own photos, even to test. I will be going to a photo kiosk in my pharmacy, i printed a fair few photos, Some just under the A4 size. And they do great, and i just looked at the PPI for them and they were low as 72PPI and as high as 350PPI. I cant really tell if their is any image loss or not. And i dont really resize my photos(lately i have but wont be anymore). If i do need to resize for the internet than i will save it twice, one for the original size and one resized for the net. This way if i am going to print it out, i can find out the biggest print i can get and work down from there to get the size i need. Well, i geuss that answeared my question haha. Thank you all for helping out.

[herbert]

Pixels per inch = pixels / inches

So

Pixels = inches * pixels per inch
Inches = pixels / pixels per inch

With three things to consider you need to decide on two and then you can work out what the other one will be.

The second question is what ppi you need. So I took this from Northlight Images:

Viewing Distance (inches) : Resolution ppi
6 : 1145
10 : 687
24 : 286
36 : 191
60 : 115
120 : 57
600 : 11

As you can see, the further away you are the less resolution you need. E.g. Huge bill boards are not printed at 300 ppi because you cannot see the difference from where you stand.

The formula is ppi = 1/((distance x 0.000291) / 2)

Hope that helps.

Alex

[DanK]

If you are sending to a good lab, and not printing yourself, all you really need to worry about is having enough detail. I usually print myself, but when I use a lab (Bay Photo), their instructions are to send the largest file you have. they take care of reducing it appropriately. However, if you have too small a file--too little detail--you can run into problems. Here is a useful guide for minimum file sizes that Smugmug provides for the three labs they use.

software can interpolate to upsize an image that is too small for a given print size, but I have never done that and don't know how good the results are.

[Manfred M]

thanks grumpy driver, but i must say that, im not printing on my printer, i can and have and produced great standard photo size for a album, and can go up to A4, but the price of ink(let alone how much ink it uses to print photos) is not exactly cheap, and i cant refill my cartridges, if i could i would print my own photos, even to test. I will be going to a photo kiosk in my pharmacy, i printed a fair few photos, Some just under the A4 size. And they do great, and i just looked at the PPI for them and they were low as 72PPI and as high as 350PPI. I cant really tell if their is any image loss or not. And i dont really resize my photos(lately i have but wont be anymore). If i do need to resize for the internet than i will save it twice, one for the original size and one resized for the net. This way if i am going to print it out, i can find out the biggest print i can get and work down from there to get the size i need. Well, i geuss that answeared my question haha. Thank you all for helping out.

The printers at the kiosks are ink jets as well, so everything I've written still applies.

Normally if you go to professional photo printing places, they will be able to supply you with the ICC profile information that is for the printer / paper that the use, but I would be very surprised in the people at the drug store would be able to help you, as they likely don't know. If you can find out what printer model and paper they use, you might be able to find this information on line. I will use an inexpensive third party (Costco) stuff I don't feel like printing myself and get their profiles by location from http://www.drycreekphoto.com/icc/ . The ICC profile will have a far larger impact on your image quality than your dpi concerns. I do using the proofing functionality in Photoshop to emulate my prints and will tweak them based on the paper and printer I am using.

Don't forget that your computer screen uses a back-lit additive (RGB) transmissive process to show you the image. Viewing a print is reflective, and the inks are really a reflective process, more akin (but not quite the same as) the CMYK used in a printing press. Your printer will have yellow, magenata, cyan and black cartridges (higher end printers have more cartridges. My Epson 3880 uses eight cartriges; black, grey, light grey, vivid magenta, light magenta, cyan, light cyan and yellow). The white comes from the paper colour and the various inks are laid down to change the colour of the light that is reflected back.

If you are printing A4, that is really a very small print and you really won't see any image quality issues. Images out of camera phones and point & shoot cameras are around 72ppi, and will be the bulk of the business for the kiosk printers. If you are worried about quality, a better print supplier would be where I would go before I worried about dpi conversions, as per my previous comments. If you are satisfied with the drug store quality, then by all means get your work done there.

[Polar01]

Allen: when you open in RAW at the bottom of the screen, if you click on that you can set your RAW preferences, simple set PPI to the value you want. Then every time you open a file in RAW the PPI will be whatever you set it at.

Cheers:

Allan

[Jestertheclown]

Have a look at this.

[Manfred M]

Have a look at this.

Good article and right on given the parameters the author is writing about. The only caveat I would make is that what he says is all about small prints (or images viewed on a computer), where the image data can be downsampled without a hit on quality. If you are looking at very large prints, you do want to provide your printer with all the image data available to maximize image quality.

[Ady]

The printers at the kiosks are ink jets as well.

Most of the kiosk printers I'm aware of are continuous tone (often a ribbon based dye-sub) rather than inkjet. Not that it makes much difference, but continuous tone prints do seem to be a bit more forgiving with less than optimal image resolution.

Cheers,
Adrian