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Subject:Re: Resolution of graphics for printed docs From:Bill Swallow <techcommdood -at- gmail -dot- com> To:"TECHWR-L" <techwr-l -at- lists -dot- techwr-l -dot- com> Date:Wed, 5 Oct 2005 13:54:26 -0400
> Pixel Dimensions: 505 W x 314 H pixels
> Print Size: 7.028 W x 4.361 H inches at 72 ppi
> The file size when saved in Photoshop format is 152 K
>
> After only doubling the resolution to 144 ppi (with bicubic resampling
> turned on), the file size jumps to 784 K! Details:
>
> Pixel Dimensions: 1012 W x 628 H pixels
> Print Size: 7.028 W x 4.361 H inches at 144 ppi
> The file size when saved in Photoshop format is 784 K
>
> Notice that the pixel dimensions changed but the physical size remained
> the same. The resampling process added more pixels to the image,
> increasing its file size.
Actually, you increased the physical size of the image because the
physical size of an image is in pixels and not in inches. Inches is
merely an output reflection given the number of the pixels and the set
ppi. So basically you distorted your image by "stretching" it
(bicubicly) to increase the pixel count and then cranked up the ppi
setting to normalize it for output. Essentially, you did a lot of work
to get a distorted image.
> If you repeat the test but this time turn bicubic resampling off, here's
> what you get:
>
> Pixel Dimensions: 506 W x 314 H pixels
> Print Size: 3.514 W x 2.181 H inches at 144 ppi
And what if you play with the ppi without altering the pixel count?
THAT is the only way to losslessly (word?) scale a graphic.
> The file size when saved in Photoshop format has stayed at 152 K, but
> that's because the print size was cut in half! This happens because
> Photoshop isn't being allowed to use resampling to create more pixels, so
> it's forced to size the image smaller to increase resolution, which is why
> the file size doesn't increase.
>
> So you can't add more resolution without increasing file size or reducing
> image dimensions.
Of note, there is absolutely, positively, no way on earth you can "add
resolution" to a screen capture. The pixel dimensions at the point of
capture are the absolute clearest they will ever be. Adjusting ppi for
output adjusts output size without affecting image clarity (or what I
think you're referring to as "resolution"). What you're doing in
Photoshop is distoring the image by adding or removing image data.
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