Re: Resolution of graphics for printed docs

Subject: Re: Resolution of graphics for printed docs
From: "T.W. Smith" <techwordsmith -at- gmail -dot- com>
To: "TECHWR-L" <techwr-l -at- lists -dot- techwr-l -dot- com>
Date: Wed, 5 Oct 2005 12:36:30 -0400

Chris.

Consider this. In the first instance, you had 505 x 314 pixels, for a
total of 158,570 pixels. In the second instance, you had 1012 x 628
pixels, for a total of 635,536. You added 476,966 pixels. Nobody is
disputing the fact that file size increases if you add pixels.

With your original image, try this (my instructions based on PS 6),
click Image > Image Size, turn off Resample Image, change the
resolution to a higher number, click OK.

You will find that the resolution of the image changed but the number
of pixels and size did not change. This, btw, is how changing the
object properties dpi setting in FrameMaker does things, it changes
the resolution hint without adding or removing pixels.

Go here and check out Screen Captures 102.pdf:

http://www.techwr-l.com/techwhirl/magazine/technical/screencapgraphicshomepage.html



On 10/5/05, Chris Christner <cchris -at- toptechwriter -dot- us> wrote:
>
> Hi TW,
>
> > Chris' post contains one, possibly more errors, such as the idea that
> > changing resolution increases file size. Changing resolution has no
> > effect on file size. Adding pixels will change file size. Adding color
> > will change file size. Changing file format will change file size.
> > Changing resolution does not.

<snip>

> Ohhkay, I just did this experiment using the same screencap of a dialog
> box I mentioned in my previous post, the dimensions were:
>
> 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.

<snip>

> 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.

======
T.

Remember, this is online. Take everything with a mine of salt and a grin.


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