OK. Say I take a RAW image with my EOS 400D. Eventually I want to make an A3 exhibition print of it at the highest possible quality, using a commercial printing service.

1. When converting from RAW into 16-bit TIFF, I am given the option to set the resolution of the resulting file, up to 8000ppi or something. Should I always go for the max resolution?

2. Is 16 Bit TIFF the best file format to work with for altering the file in Photoshop?

3. I understand that printers print at 300dpi. Do "dots" equate to "pixels" in this notation, in other words, is ppi equivalent to dpi? If this is the case can't I just save my photo at 300ppi rather than 8000 or whatever?

Please make your answers as technical or as simple as you like - I can handle the science and I want to learn

StickyShutter:

OK. Say I take a RAW image with my EOS 400D. Eventually I want to make an A3 exhibition print of it at the highest possible quality, using a commercial printing service.

1. When converting from RAW into 16-bit TIFF, I am given the option to set the resolution of the resulting file, up to 8000ppi or something. Should I always go for the max resolution?

PPI refers only to screen resolution, as the output, the print works in DPI.
You can set your PPI to 8000, but your shot will remain the same size on the screen, but you'll probably be told you'll get a tiny print.
Theres a debate on it here.
300dpi/ppi is a good starting place, as you can downsize to 254 for prints, as I do, or 72 for web stuff, so people cant print big version.

2. Is 16 Bit TIFF the best file format to work with for altering the file in Photoshop?

Yes, basically.
16bit files have twice the amount of data for each channel then 8bit files, So the file will show better results when you modify it, better gradients and such.

3. I understand that printers print at 300dpi. Do "dots" equate to "pixels" in this notation, in other words, is ppi equivalent to dpi? If this is the case can't I just save my photo at 300ppi rather than 8000 or whatever?

Despite what most people on there will say, once you get past 254dpi, theres no real difference. Cameras files, in my experience, are set at 254dpi. So setting 300dpi will just make the print look better quality, as the dots will be closer, cause your maximum print size will be lower, according to what photoshop will say it can do "well".
All my works at 254dpi, and I've had 20x30in prints made from my 10mp D200, with no real loss in quality, of course it depends on the individual shot.

Please make your answers as technical or as simple as you like - I can handle the science and I want to learn



Sorry for not being too clear...

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Matt Harris Photography
The Crusade for Photographers Rights
Support a Needy Artist?

DPI = dots per inch = printer setting and determines how much ink is put down over a given area. You've already ascertained that your printers default setting is 300dpi (dot per inch).

PPI = pixel per inch = resolution setting = quality of viewing. Example: Canon 40D, 10 megapixel camera, 3:2 aspect ratio, at large/fine setting gives 3888 x 2592 pixel. Choosing a resolution of 240ppi (pixels per inch) gives 3888/240 = 16.2", and 2592/240 = 10.8". So in short setting a resolution of 240ppi will give you an extremely good print size of 16 x 10.8". By lowering the resolution to say 72 (just for example) will give you a print size of 3888/72 = 53", and 2592/72 = 36", or a print size of 4.4 ft x 3 ft.

Whilst 72ppi is generally good enough for a monitor consideration should be given to the distance the final print will be viewed from. If you stand nose up to a 4ft x 3ft print you'll not only not be able to see the entire print but you will be able to see every pixel. Standing back a bit of say 6 ft - you now will be able to view the entire print but you will be hard pressed to see every pixel. In short, make your ppi based upon the output of the image e.g. only for monitor/web viewing or if print, what size and what viewing distance.

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Thank you to you both for taking the time to write such thorough replies. Sorry to be an idiot but I'm still confused though over the relationship between ppi and print quality. I think I'm getting there, though...

Am I right in saying that saving a file at a low resolution (such as 72ppi) does not take information (ie quality) out of the image, it just makes the pixels bigger, therefore making the image larger?

Does viewing resolution matter at all, then, given that then pixels can be stretched/squashed at any time, to make any print size, without loss of image quality?

OR do I need to choose the right resolution when I first create the TIFF from the RAW file? (ie, "I'll be making an A3 print of this so I need a resolution of  x ppi").

Mattharris - you say that you choose 72ppi for the web so it's small, but Alan you say you would choose 72ppi for a large exhibition print because it's big. Is one of you wrong, or have I just not understood the principle?

Durrrrr my brain hurts

StickyShutter:

Mattharris - you say that you choose 72ppi for the web so it's small, but Alan you say you would choose 72ppi for a large exhibition print because it's big. Is one of you wrong, or have I just not understood the principle?

The larger the print, the further back you'll stand to view it normally, so lower quality + huge print can work together.
But I mean when you're doing shots to put on a website, you can put them at 72dpi, so if someone saves it, and tries to print it large, it will be really bad quality, as you've saved the image at say, 800x600, to get an A3 print you really need about 6 megapixels, which is 3000x2000, if you upsize the file from a 72dpi image, the quality will be terrible.

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Matt Harris Photography
The Crusade for Photographers Rights
Support a Needy Artist?

StickyShutter:

Am I right in saying that saving a file at a low resolution (such as 72ppi) does not take information (ie quality) out of the image, it just makes the pixels bigger, therefore making the image larger?

If you start off with a 1 litre can of white paint and start to cover a wall that was previously painted black then provided you don't dilute your paint you stand a good chance of the black not showing through. You might consider this paint then to be of a resonable quality. Dilute the paint now to 1 part water and 1 part paint then it stands to reason that you'll be able to cover twice the area of black wall. However, your paint will probably now be applied so thin that the previous covering of black shows through. No doubt you would consider this to be low quality.

Now you have to imagine you are viewing a photographic print that has been pinned to the wall. Let's say for example that this print is of a size of 6" x 4" and I place a 1 pixel size blob of white paint somewhere on the print. I ask you to view this print from a distance of 100 yards. I think it would be quite reasonable to say that your chances of spotting this 1 pixel blob of white paint would be nigh on impossible, yes? Obviously the closer you get to the image the more likely it is that you will start to spot where this blob of paint has been placed. So distance of viewing is a major consideration when choosing resolution. You can afford to choose a lower resolution setting i.e. less pixels spread over a given area if the print is to be viewed from a distance. It it is to be viewed close up then the resolution needs to be increased. An exercise for you to demonstrate this. I have no idea at what distance you are now viewing your monitor from but it's a good guess that you are unable to see, let alone count the number of individual pixels on your screen. Now move in closer to a distance of say 3cm from your monitor screen and you should now start to see little specks as though your eyes are playing tricks with you. In short then, if you are going to be viewing a print from very close up then you have a choice of making the print very small and cramming more pixels into every inch or making a much larger print, say 10" x 8" with less pixels per inch but with the proviso that the print will be viewed from a greater distance.

Mattharris - you say that you choose 72ppi for the web so it's small, but Alan you say you would choose 72ppi for a large exhibition print because it's big. Is one of you wrong, or have I just not understood the principle?

No I didn't say that - you have obviously misunderstood. I can produce a much small image having a higher resolution than someone creating a much larger image but using a lower resolution. In the end they will in effect both be equal depending upon the viewing distance. Producing an image that is twice the size of your average monitor using a high resolution makes no sense so why produce it in the first place? Creating a 72ppi image that happens to coincide with the resolution of the bogg standard monitor makes far more sense for web use and it also helps to discourage somebody else downloading your image e.g. stealing it and printing it out for themselves. They are hardly likely to produce a wall-size poster from a 72ppi image although believe it or not, it has been known. How that is possible though is for another day.

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A pixel is a square block of colour, but in print will show as a single dot of colour. Therefore a pixel equals one dot on the printed page. If printing on A3 then 254dpi is best quality. Use Photoshops image size options to increase the size, to fit A3 by entering this size in the width box. Make sure the three boxes, Scale Styles, Constrain Proportions and Resample Image, are ticked and Bicubic is selected in the dropdown box.

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SK
The Best Photographer in the world 4th November - 5th November 2006 & 17th-18 November 2007
Oldboy’s Gallery

StickyShutter:

Does viewing resolution matter at all, then, given that then pixels can be stretched/squashed at any time, to make any print size, without loss of image quality?

OR do I need to choose the right resolution when I first create the TIFF from the RAW file? (ie, "I'll be making an A3 print of this so I need a resolution of  x ppi").

Viewing resolution matters so you can see what you are working on - but PS and other image-editing software generally make most images fit the screen you are working on (unless they are too small - they won't routinely stretch them beyond 100%). As others have said, pixels have a finite size but you can use software to add them or take away, making the picture larger or smaller: image quality may be compromised if you overdo it.

I always work initially on the full image as captured - that is, I make minor corrections such as taking out dust spots and basic exposure adjustments and maybe cropping or any other changes that I want to apply to any version of the image. I then resize the picture so it's the right size for the format(s) I'm going to be outputting it to, make one or more copies at the appropriate size and work on the copy for print or web as appropriate. I do sharpening, framing and other finishing touches on that version.

I use this workflow because I then always have a master version I can return to and resize or rework as necessary as well as the finished print or web copies. Others will have different systems that work for them.

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My DCM Gallery

mattharrisuk:

Yes, basically.
16bit files have twice the amount of data for each channel then 8bit files, So the file will show better results when you modify it, better gradients and such.

Just a minor technical correction. 8bit files have 256 levels - 16bit 65536 levels - however most cameras record 12bits of data resulting in 4096 levels if recorded as RAW/Tiff. Newer cameras record 14bits, which is 16384 levels.

But the principle of having better gradients etc holds true.

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Mark

Digital Photo Group
My Website

Ne nuntium necare

Another technical point: most pro-labs still print at 8 bits per channel, so any 16 bit files they will recieve will be dummed down to 8 before printing.  I think some printers use 12 bits, but 16 bits is something for the future I believe.

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[Digital Black and white]

OldBoy:

A pixel is a square block of colour, but in print will show as a single dot of colour. Therefore a pixel equals one dot on the printed page.

Sorry to disagree with you OldBoy but as most inkjet printers output at 4800 x 1200 dpi ( dots per inch) then a image that has a resolution of 300 ppi (pixels per inch) will have more dots per inch than it has as pixels!  A pixel equals a pixel on the printed page not a dot, many dots can go in to make a pixel.

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Paul
My glass is 4/3rds full :)

MY GALLERY

My DCM Gallery