African Watercolor, Part 1
Interview with Marley Mcleay
News for November
Having a Hobby
Unraveling DPIAsk an Artist
by Annie Rodrigue
This month, I decided to treat a subject that seems to confuse a lot of artists who want to scan and print their work: the whole notion of DPI (dot per inch). I'm no expert in the matter, but I will try to explain it the best way I can, with a bit of help from our friend Wikipedia.org!
A Common Mistake
People often relate pixels and resolution. They will ask how big an image needs to be in pixels so that it is at 300 dpi, for example. But in fact, DPI is a resolution that relates to inches. As for pixels... well, they are a type of measure just as inches are, so it's not possible to relate DPI and pixels together. You can only relate the DPI to the size of the image in inches, and then you can get a size in pixels, if you need this extra information.
Dot Per Inch
Put simply, "dots per inch" is literally the number of dots you can put on the span of 1 inch. The lower the resolution (for example, 72 dpi is very low) the bigger the dots and the easier they are to see with the naked eye. And of course, the higher the resolution, the smaller the dots will be.
When it comes to printing or scanning, what resolution should we go for? There are standards in the industry, and printing companies will have instructions to follow. Same goes for your own printer. The most common resolution is 300 dpi. Printing companies will usually ask for at least that much. Most high quality inkjet printers will not go under this resolution either.
The resolution you pick when you scan your work can come in handy though if you put a little thought into it. Scanning at 300 dpi doesn't quite give you to chance to play around with your work when you think about it. If you need to stretch or re-size at a bigger scale, you will not be able to without losing some quality in your work. I guess I try to cover my grounds in case of emergency, but I always scan at 600 dpi, especially with my smaller work. This will give me the stretch I need when I want to enlarge my work to greater proportions.
Just a few weeks ago, I wanted to print my 5"x7" paintings as wall scrolls. The printing company only asked for 150dpi. This is great because that means I can make my illustration much larger that way! After playing with the resolution, my illustration could be printed at 20x28 inches. But how is that possible? This DPI to inches conversion is like this magic trick where you can lower the resolution to enlarge your canvas. As long as the resolution is of high quality, your work will print beautifully! Here is how it's done:
In our example we have the 5x7 inch painting. This is the image's information in Photoshop. You simply have to go to Image > Image Size.
So you can see the size of the image in pixels at the top, and in the middle, the size in inches with the resolution. Now, if you uncheck the setting "Resample Image", this will block the pixel size of the image and leave you with the resolution and size in inches only.
You can then change the resolution to 150 dpi, and automatically, Photoshop will change the size of the image to 20x28 inches! Simply click OK to apply the changes!
This little trick applies also if you want to go the other way around! A good example: most digital cameras will save photos at a huge size, but it will be at 72dpi. You can raise the resolution of that file in Photoshop so that when you print it at a reasonable size it will be of great quality printing!
Resolution of a Screen VS Resolution on Paper
I couldn't help going on Wikipedia.org to make sure the information I was writing was clear and correct. But while checking, I also learned a thing or two! And so, it was so clearly explained why a computer screen didn't need more than 72 or 96 dpi resolution compared to a printed image, which require 300 dpi. The reason was simple enough, a computer screen will work with millions of colors compared to a printer which will only have 6 or 7 cartridges, and so only a very limited range of colours (no more than 128 or so) . Because of this a screen can create a gradient much more efficiently with a lot less dots, while a printer will need much more dots using its limited range to create that very same gradient.
They have this very clever image to explain it. I'm including it here, I hope it's allowed. All credits goes to Wikipedia.org for this one!
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