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Upscaling/Resampling Badness and Why DPI Doesn't Matter
Take a look at these glorious shots.
Beautiful! Great color, detail, and composition.
But there's more than meets the eye at play here...
Here's a 100% crop of this photo:
Pretty sharp, nice detail, very little grain...
And from this photo
Same here, good detail, could use setting the black point, a touch of post processing, light sharpening, but super straight out of the camera...
And from this photo
Oh no! What happened?! Look at the JPG artifacts, the jaggies, the blurriness! Help!
There's the culprit! Resampling! When we do this, we can put any values we want in the height, width, or DPI fields and Photoshop won't argue. Photoshop will invent the image specifications you tell it to.
In this example, we first resized the image to 8x12 (this is PRINT size). We then changed the resolution to 302 PPI. Both of these were done with Resample Image ON.
Here is our new 100% crop. When resizing the image to 8x12 output print size, we lost a LOT of pixels. Then when changing the PPI from 72 to 302, we 'invented' a lot of pixels and we see our result here. Fuzzy, grainy, yucky badness, when we had a super image to begin with. All due to that pesky Resample box.
Had we just unchecked the resample box, it would have simply rearranged the pixels we had in a non-destructive way. But, there is really no reason to do any of this, and we'll tell you why...
Let's start by turning off the badness. When we choose not to resample, we'll be working with the original pixels only. Nothing will be cut, nothing invented.
Here, we change the resolution to 302 PPI. Notice how the pixel dimensions 3888x2592 do not change. Also notice how the document size, our print output size, DOES change.
Why? This takes a little bit of simple math. Lets remember what PPI and DPI mean. PixelsPerInch, and DotsPerInch. They're almost interchangeable terms, but one pertains to the screen, and one to printed output (DPI).
Have we really done anything here? Nope. That's all this is doing is changing some text markers in the Metadata. Lets come up with some simple figures to look at.
Here, we've taken the same settings, but instead changed the print output size to an exact 8x12. Notice how the resolution now jumps to 324 DPI/PPI. Still, have we done anything? Nope.
Lets take for example a simple 2:3 photo. We'll say at 4"x6" it is 100DPI in resolution. This translates to 400x600 in pixel dimensions. 4in x 100 dots per inch = 400 pixels. With resampling OFF, if we change our DPI to 200, we now get an output size of 2" x 3". 2 inches x 200 DPI = our original 400 pixels. Same pixels, same dimensions, just rearranged and smushed closer together for 'finer' detail in a smaller print.
But you ask, "Shouldn't I worry, and pain myself over the final output?". In short, no.
Pictured here is a screenshot of our Getting Great Prints page. Depending on the size of print ordered, different printers will be used capable of different DPI output.
Larger prints need less DPI to look great, because the viewing distance is going to be greater. You might ask, "Wouldn't 600DPI look phenomenal at any distance though?!"
Nope! At that DPI with a viewing distance of more than an inch or two, you lose the control over what your eye blends and eliminates. Pixels, tones, hues are smushed together by each viewer's brain as the human eye isn't able to discern such fine detail at a distance and has to 'dither' the data. By leaving ALL of this data and so close together, each interpretation is going to be different and due to the way the human eye reads and interprets light, you'll end up with clean lines and hard edges that fade into oblivion and crisp tones and values that mix into mud.
When using a smaller DPI, YOU decide as the print gets larger, how those dots are distributed, and give them enough room to be properly interpreted making for a great, and consistent viewing experience each time.
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