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I’ve been asked many times by friends and acquaintance about image resolutions and the resizing of images on the iPhone, and how this affects print quality, with particular emphasis on sites such as RedBubble, Zazzle, FineArtAmerica, deviantArt, etc.
In plain English - what resolution should you set your images, to sell as quality prints etc on these sites?
RedBubble’s minimum size guide is:
Zazzle’s resolution guide is:
In case you’re confused, as RedBubble speaks in terms of pixels whilst Zazzle speaks about ppi…basically, to see what the maximum size your image can be without pixellation or blurring, divide your pixels by the ppi. So, for example if your original image is 4800x3600 pixels, dividing this by 300 ppi (the industry standard for quality prints) gives you a maximum size of 16x12 inches. Zazzle claims to be able to print good quality at right down to 100ppi - so if this is true, then a 4800x3600 pixels image at 100ppi will give you a maximum size print of 48 x 36 inches. I haven’t tested this out myself, so I can’t say if the quality is as good as claimed. RedBubble, on the other hand, states that at 150ppi, pixellation or blurring may start to happen.
FineArtAmerica has a print size table, which unfortunately doesn’t fit here. Here is the link: http://fineartamerica.com/create-art-online.html Their table has a number of errors in it, though…however, the general rule of thumb is - FAA wants your images to be at least above 1800x1800 pixels.
deviantArt has a great explanation of image resolutions, and a chart showing maximum image sizes at 150ppi and 300ppi. It also claims that clear prints can be gotten from as low as 100ppi. Again, the chart won’t fit on this page, so here is the link: http://help.deviantart.com/132/
I generally go by what I call the “Rule of 300”. For convenience, I like to resize my final images on Iris Photo Suite at 1200x1600 pixels if it’s portrait or landscape, and at 1200x1200 pixels for a square format. The iPhone 4 saves at a default of 1936x2592 pixels, which, as you can see, is not easy for calculating print sizes (it come to about 6x8 inches maximum at 300ppi). Saving at the resolution I choose means the image takes up less space on my iPhone 4, allowing me to store more images in its memory bank…I’ve had 6000+ images on my iPhone 4 without any problems with storage space.
I’m not sure of the mechanics of it, but resizing the image larger, for example, from 1200x1600 pixels to 3600x4800 pixels on the iPhone 4 (using Iris Photo Suite) before transferring it to the computer, does not seem to affect the sharpness or quality of the image. I think this could be because the pixels are there all right, just compressed, and resizing the image upwards just makes them expand a little more. (Similar to creating a Zip file, perhaps, which compresses the information, but allows it to be de-compressed or Unzipped at the receiving end without loss of information). It’s NOT the same as resizing a low-resolution image to a high-resolution, where there are not enough pixels to go around, so the pixels explode outward into empty space, causing pixellation and blurring. Like I said, I’m not an expert, but this is my theory, it works for me just fine, so if it ain’t broken, don’t fix it! ;-)
I’ve read on some photography sites that resizing of a photo should be done BEFORE attempting any modifications to the image. This may hold true for traditional Photography, I’m not a photographer so I can’t comment on that. However, the way I process my iPhoneography images is, I tend to run them through at least 3 if not more Apps, before finalising them. The way I look at it is, each time I add a filter or effect, I’m effectively adding more pixels to the mix. When I’m done processing, the “pot” will be so full of pixels that resizing it larger should not cause pixellation or blurring. And that’s why I always Resize LAST.
Hope this helps! :-)