Preparing an image for fine art print -- dpi?

A local artist has asked me to photograph her artwork for possible mass reproduction. It seems the artwork needs to be in a tif file with 300 dpi.

I did some test shots with my Rebel xti (using the 24 105 is because it seems to give the best results). The RAW files show a 300 dpi but image size of 7 x 11?????

Rachel, this will not be trivial There are a number of potential issues

- depending on the surface of the artwork the lighting may be difficult if you have to deal with specular reflections. You may need big diffuse lightsources.

- you will need to ensure consistent and accurate colour rendition - flash may be a help here and some form of camera profiling

- for artwork reproduction I would be inclined to stitch shots so you get the 300dpi at original resolution. That is I wouldn't take a picture of a piece that is 18 by 12 for example and resize the file, but I would set up to shoot 4 (or more) overlapping shots and then stitch. That way the artwork will be reproduced more accurately. You will need to make sure that the artwork is parallel to the sensor. You may find it easier to moce the artwork around the wall and leave the camera on a tripod.

- I would shoot this with my 100 macro. The issue with the 24-105 may be that it has some degree of barrel distortion.

Also, provided you can get good focus on the work and it doesn't have much depth (oils for example) don't stop down too far. This because you don't want to discard resolution to diffraction.

Go for it and enjoy

Mike

Rachel Foster said:

A local artist has asked me to photograph her artwork for possible mass reproduction.

Click to expand...

Hi Rachel,

I agree with Mike, it won't be trivial.

The best approach is to work your way back from what is needed. How large need the reproductions to be? What printng requirements are there, and what technology will be used? Derived from that you'll be able to calculate the number of pixels per dimension of the artwork, and take a safety margin to allow for losses in the process.

Then determine which capture requirements are needed to meet those specifications. Maybe stitching is needed, it would also take care of lens distortions, and it allows to square the final image. How about lighting the artwork?

Many questions need to be answered in order to come up with a battleplan, and there is a learning curve involved.

Bart

Ah, good old relative and absolute size.

Anything labelled with dpi, lpi or ppi is relative size, which only bears if you have to stretch or compact the pixels in your image to a pre-defined standard. The number of pixels in your image is absolute - there's no more, no less.

Despite us buying monitors based upon their physical dimensions - 17", 20" asf - they are really absolute, that is like your image they have a specific number of pixels, no more, no less. Hence your image is shown pixel by pixel, not in relation to inches.

Thus, relative size comes into play when printing, since paper does not consist of discrete pixels but is an analogue medium defined by its physical dimensions.

Let's not dwell too long on the differences between dots, pixels and lines, just say the first two are 1:1 equivalent, the latter stands in a 1:2 relation and is only necessary to know for professional printing houses. Your printer translates the pixels of your image into [many-layered] dots.

Every inkjet printer has a physical limitation - the number of tiny holes through which the ink is pressed. This is its native resolution, depending on maker this goes from 240 to 360, with some higher end Epsons having 720, Canons and Hewlett-Packards can go up to 600. That's all dpi.

The higher numbers touted for printer res, i.e. 1440 and 2880 for Epson, are shorthand for the multi-layering resulting in smooth gradations.

While image files usually contain a relative resolution number, from 72 to 300, this has no meaning. AFAIR, only Photoshop might use it as the default when you print but forget to set the relres.

For your photography that means: don't fret over relative resolution. It has no bearing on taking the picture. What you should fret over is your technique. Use a solid tripod with an even solider [sorry] head, stop down your lens two or three stops but not more unless absolutely necessary [same holds in the opposite direction], use a remote release, etc.


PS: If you are interested to learn more about printing with SOHO devices, you might want to have a look at Mike Chaney's column over at Steve's Digicams under Tech Corner.

You could check this web site from someone who does it for a living. Bascially they photograph art for art fair juries, but that has to be the highest quality reproduction because of the competition. Not sure if you're asking about print sizes or just photographing art, but here's something since it's part of the equation:

http://www.bermangraphics.com/artshows/photographart.htm


Mike

Hi Rachel,

You have been given excellent advice by the gentlemen before me. But I know how confusing it can get reading this all new information, part of which can go way over one's head ;-).

So let me give you an actual example:

You have a Canon XTi. It takes pictures which contain 3888 x 2592 pixels.
So the longer part of the image is 3888 pixels.

Let's suppose you want to have a publication quality print made from your image.
This print will then contain some 300 dots in every inch, along both dimensions. This is what they call the 300 dpi.

So the calculation of the print size is:
Print size = number of pixels divided by dpi
Length of the print = 3888/300 = 12.96 inch
Width of the print = 2592/300 = 8.64 inch

Now suppose that you want to make a print having the same quality (i.e. 300 dpi), but must be 24x17 inch. In that case, you will then have to double the image dimensions, so it will contain 4 times more pixels than what you've started with (2x2=4). In other words, you'll have to have an image which contains 3888x2 x 2592x2 pixels (7776x5184 pixels).

But how do you double the image dimensions? There are vaious ways. One way (not recommended) is to resize the image in PS or in another image processing program. This will create pixels where they did not exist and is not the ideal solution for fine art replication.

Another way is to take 4 pictures, each one covering around 1/4th of the image and then stitching them in the computer. This would be the recommended method.

I hope this has clarified things a bit for you and did not achieve the opposite ;-)

I have an email and sample into the publisher the artist is using. Reflections and color are not an issue at this point as I used soft-box lighting and the art is watercolor. Also, good tripod with remote release and I think as far as that goes, no problem.

The size at 300 dpi though may be. Luckily, a local pro has agreed to help me if I run into trouble. I think I'm going to give him a call since the stitching is a touch intimidating.

Hi Rachel,

a little late, but just another thought for the future, depending on your contract, it might make perfect sense to get a high resolution scan instead, obtain the TIFF file and of you go.

The reason I am suggesting that is your mentioning of watercolor, this usually uses paper that can be rolled without damage, hence is suitable for high resolution scanning.

It eases your workflow and gives you a perfect file to work from without spending a lot of time on setup, light, stitching etc.