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10-06-2010, 04:26 PM   #1
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Question about pixel dimensions/image size etc.

I am trying to understand the relationship between pixel count, optimum print size, maximum print size, how Photoshop determines the size and a few more related things. I will be exhibiting my photos so I need to know what the best size is going to be for printing. Not that size is everything, but I would like to knwo what my options are. I have looked at some threads and some, OK a lot, of it went over my head so I am asking some specific questions which make sense to me to ask.


So - I am shooting in .dng from a K7. The size in pixels is 4672 x 3104. Because my version of Photoshop, ver 7, cannot read Raw files, I have to open them in the Pentax DCU and then save out them as 16bit Tiff’s. Photoshop automatically opens this as 262.81 x 395.56mm @ 300dpi, with the same number of pixels (almost A3 size). I try to do any Photoshop work in 16bit mode
I am showing soem photos in an exhibition, most of them will be colour. I hope to be able to get at least some of them done as giclee prints. I tend to crop my photos, either modestly or drastically.


Q1 - Is this size,(262.81x395.56mm @300dpi) the optimum size for printing?

Q2 - If I get a print done at A2 - will the photograph look horribly pixelated, or will it be acceptable for an exhibition print? From what I read this should be ok.


Q3 Can I just increase the dpi in the image size to get a better quality print at bigger sizes? (From what I read this doesnt matter - but I dont understand why.)


Q4 Or should I increase either the pixel dimension or the document size to get a bigger sized print?(From what I read its best to hand the file to the printer who will resize it for me)


Q5 Or should I create a new document at A2 size, and then drag the tiff into that document and resize it. Is this increasing the pixel dimensions?

Q3 - In the image size menu, if I increase the pixel dimensions, the document size increases. If I increase the document size the pixel dimensions increases, however - if I increase the dpi, the pixel dimensions change, but not the document size. What is going on here?

Ok that’s enough for now I think. If anyone can explain this in reasonably simple language I would be very grateful.

Graham


10-06-2010, 04:48 PM   #2
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QuoteOriginally posted by grayboy Quote
Q1 - Is this size,(262.81x395.56mm @300dpi) the optimum size for printing?
Depends on a) your printer, b) how much work you put into optimizing for printing, and c) how closely and critically it will be viewed. But 300dpi is a decent rule of thumb for good quality.

QuoteOriginally posted by grayboy Quote
Q2 - If I get a print done at A2 - will the photograph look horribly pixelated, or will it be acceptable for an exhibition print? From what I read this should be ok.
A2 is about 23.4×16.5". Assuming you crop the paper to 3:2 ratio rather than cropping your image, that's a 23.4×15.6" print.

4672 pixels divided among 23.4 inches is 199.658 dots for every inch: 199.658dpi, or for all practical purposes, 200dp.

Same way in the other dimension: 3104 pixels /15.6" = 198.97 per inch; round to 200dpi (and don't worry about being over-precise).

Generally, printers can do 200dpi very well. There may be a loss of sharpness vs. 300dpi, but from most viewing distances you won't notice.



QuoteOriginally posted by grayboy Quote
Q3 Can I just increase the dpi in the image size to get a better quality print at bigger sizes? (From what I read this doesnt matter - but I dont understand why.)
DPI isn't magic: it's just dots per inch. How many dots do you have, spread out over what size paper?

So, if you increase the DPI, you have to either get more pixels from somewhere (hard) or reduce the size at which you're printing (easy, but not necessarily what you wanted).


QuoteOriginally posted by grayboy Quote
Q4 Or should I increase either the pixel dimension or the document size to get a bigger sized print?(From what I read its best to hand the file to the printer who will resize it for me)
Don't mess with it. Just make sure you have enough data for the print size you want.


QuoteOriginally posted by grayboy Quote
Q5 Or should I create a new document at A2 size, and then drag the tiff into that document and resize it. Is this increasing the pixel dimensions?
Possibly, depending on the settings. But you can't make up more data where there isn't any. If you resize to bigger than your original, the computer just guesses — usually, by introducing blurred pixels in the middle.

QuoteOriginally posted by grayboy Quote
Q3 - In the image size menu, if I increase the pixel dimensions, the document size increases. If I increase the document size the pixel dimensions increases, however - if I increase the dpi, the pixel dimensions change, but not the document size. What is going on here?
Math.
10-06-2010, 05:05 PM   #3
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Well maths was a long time ago for me, I remember log books and slide rules. Never sure how to use them though. Thaks for the reply, I will read and try to understand.
10-06-2010, 05:08 PM   #4
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QuoteOriginally posted by grayboy Quote
Well maths was a long time ago for me, I remember log books and slide rules. Never sure how to use them though. Thaks for the reply, I will read and try to understand.
The key point is it isn't hard — it's just basic arithmetic, with no slide rules or logarithms required.

10-06-2010, 05:58 PM   #5
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Hi grayboy,

You have a lot of good questions. I'll try to answer some, but I'll answers others too. To support my photography work 25 years ago I was a professional picture framer. Even today I still usually frame my own work for exhibitions most of the time.

The optimum size for printing really depends on the content of your image more than anything. Some subjects, like large-scaled vistas look better larger. Other shots, like an intimate closeup of a delicate plant or flower may be better smaller. Smaller prints tend to draw people's faces closer to the work (so make these super flawless!). Sometimes a small print and a large mat works better. It's an subjective call ultimately, but I would seek out opinions from respected artists (and not necessarily loved ones) who you can physically show the prints to.

Let's get the nomenclature right: it's really PPI (pixels per inch) that you need to be concerned with. DPI is a misnomer of sorts dating back to scanning resolution and laser printing/desktop publishing days in the mid-to-late 80s. Hopefully all the printers you will be using have sufficient DPI.

Oh, and another thing, giclee, is a buck-twenty-five word for ink-jet. Most digital prints these days are ink jet, though many cheaper Costco or drugstore retailers have very nice old style printers.

Your camera, like most APS-C and FF DSLRs (excepting 4/3rd) utilizes a 3:2 aspect ratio. That would allow images with corresponding dimensions to be output at 4x6, 6x9, 8x12, 12x18-inches for example. These sizes are becoming more standard in framing materials and printing paper.

The old commercial sizes such as 8x10, 11x14 etc. require cropping of your image to fit. While some images are improved that way, I try to set up shots to utilize the whole frame. If you do too, I would recommend you output your prints at at 3:2 aspect ratio. It's cheaper to purchase standard mats, backing boards, frames, glass, and printing paper.

Regarding output resolution, basically the larger the print, the lower PPI is necessary. That's because people have to get closer physically to a small print to perceive it well enough. So a 4x6 should be output at 300 ppi at least.

And printing images that have ppi exceeding say 350 doesn't improve the quality of the print in most situations. You consume more ink and printing takes longer due to more useless data to crunch.

I hesitate to recommend hard and fast rules here because some software is better than others at squeezing resolution out of smaller files; some professional printers (the people and the devices) are excellent too. And your sharpening techniques help here a lot.

I've output very acceptable 12x18 color prints at 170-200 ppi. Generally at that size 250 ppi is the default provided you didn't snip away part of the image. Do note, the larger the dimensions the thinner they are spread across the space of the frame, so your ppi will be a smaller number.

In Photoshop you can play around with the dimensions to see the resulting PPI; just make sure you click the Constrain Proportions box and uncheck the Resample Image box.

I wouldn't worry about the document size. That's important if you are printing at oddball, non-standard sizes and need the extra real estate. You will be trimming the sheet of paper holding the final image most likely anyway to a small even border.

16x24 is close to A2 and will get you about 188ppi. That should work if you are smart about the post processing. With 3-4-in borders, your total materials costs will be fairly high if you use decent stuff.

Questions for you: How broadly are your images cropped? who is doing the printing? What printer is being utilized? What kind of inks? what is the gallery lighting like? If you are printing, is your monitor calibrated with a hardware device?

Hope this helps.

M
10-07-2010, 07:15 AM   #6
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@Mattdm -
QuoteQuote:
Depends on a) your printer, b) how much work you put into optimizing for printing, and c) how closely and critically it will be viewed. But 300dpi is a decent rule of thumb for good quality.
By optimise do you mean sharpen/curves/levels?

Originally posted by grayboy
Q4 Or should I increase either the pixel dimension or the document size to get a bigger sized print?(From what I read its best to hand the file to the printer who will resize it for me)



QuoteQuote:
Don't mess with it. Just make sure you have enough data for the print size you want.
How do I make sure I have enough data? Do you mean throw away as little data as possible, so avoid converting to 8bit .tiff or jpeg?


@ Miguel
I thought giclee (point about the buck 25 word duly noted) were ink jet , but superior to standard commercial printing ink jet methods. So If someone gives me two prices for they same print, a cheap inkjet price and a more expensive giclee price - are they working a scam, or will they be using better inks and printing methods?



QuoteQuote:
I try to set up shots to utilize the whole frame. If you do too, I would recommend you output your prints at at 3:2 aspect ratio
I seem to be cropping my shots quite a bit, and so it seems that the best thing to do is to crop my photo from the original 3104x4672, and then if I want it printed onto a a sheet of say 12x18 inches, I just increase the canvas size, making sure white is selected as the background colour, and save as a 16bit .tiff. Am I right that this does nothing to the pixels, Photoshop doesn't have to resample or resize anything. Is it better to save as a .tiff or a .psd?



QuoteQuote:
Questions for you: How broadly are your images cropped? who is doing the printing? What printer is being utilized? What kind of inks? what is the gallery lighting like? If you are printing, is your monitor calibrated with a hardware device?
Most are cropped to some degree, some of them are cropped pretty drastically, but i have decided to keep them at 100% crops if I can. But I will have to resize a couple of them to get them larger. In PS7 there is a resize wizard in the Help drop down menu. Am I better to use that? Or is it the same as just resizing by using the selection tool and shift & drag the image handles to size?

I am trying to find someone to do the printing. Do different printers, the machines I mean, have very different qualities, what should I be looking out for? What different sorts of inks are there?

QuoteQuote:
16x24 is close to A2 and will get you about 188ppi. That should work if you are smart about the post processing.
Is that another reference to optimising, ie how much I apply sharpen/curve/levels etc. Or do you mean how I save the file, as a .tiff or .psd. I want to be smart - but how smart is it possible to be, and smart in what way?

I feel like I am probably asking some inane questions - sorry if anyone is getting expasperated, but some of these issues dont seem to make much logical sense. I'm sure they do to those that have a better foundation in all of this, but I feel like i am trying to fly a plane, only ever having flown a kite.

Many thanks to both of yuo for taking the time

Graham


10-07-2010, 08:43 AM   #7
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Optimizing to me means ensuring that the image is best prepared for print. It’s more challenging to prepare an image for printing than it is for simple web viewing. What looks pleasing on the screen may not be what the printer needs. Sharpening for printing is usually more intensive—especially if you’ve cropped away a chunk of the original data.

Getting the right exposure on the printed image can be challenging too—especially if your monitor has not been calibrated. Often prints come out too dark, and this is commonly attributed to a too-bright monitor.

Most of your questions are better answered by specific online tutorials, books, and printer visits, and experience.

Resizing downward within the same aspect ratio will be OK. Rearranging them is not. Grabbing handles and massaging you pixels will result in an unsharp and distorted image. Resizing upward to incorporate drastic crops is risky. You are creating new pixels, and as a novice that’s close to dangerous. Fine art prints have to be perfect. I’d leave it to a fine printer who may have better software and skills.

If you exhibition deadline is coming soon, I’d advise that you pay to have a custom lab process your images to ensure they reproduce well on their equipment.

The lab will also let you know the proper file format and color space requirements and whether your file has enough data to output at your desired size satisfactorily.

"Giclee" is not a standard product. Some printers use “giclee” to designate output on a more sophisticated printer that uses more ink carts for finer color renditions. They also may use more archival “fine art” paper that won’t fade in sunlight as quickly. Lots of variables here. Find out what printer(s) are being used.

Do you have paper types in mind? Some images look better on glossy, others matte, and some pearl.

Regarding your cropped image borders, you’ve got to make an artistic choice about what looks good with what sized white borders. Sometimes an image will look better with a large white image border; more often I see a smaller image border and larger mat borders, especially if you want the overall framed dimensions to be larger. I'd recommend checking out several photographic art galleries and see what they do.

The more customized your work is, the more expensive it will be to produce the final product. Make sure that the retail price of your print is still reasonable after figuring in commissions.


M
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