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SleepingWolf
Paranoid (IV) Inmate

From:
Insane since: Jul 2006

IP logged posted posted 09-12-2009 18:03 Edit Quote

Came across this link recently:

http://www.turbophoto.com/Photoshop-Tricks/screenshot-photoshop-trick/index.htm

They describe essentially the same technique I use, but they convert the image to Indexed Color before scaling up to 300 DPI.

code:
With an index color mode you may scale in multiples without altering the integrity of the screen capture.



Is this necessary and why? I normally leave the image as RGB.

For example, I will select a graph in Microsoft Excel and copy it (rather than a screenshot) and then paste it in PS. Then I uncheck resample and increase DPI to 300.

Also they claim that 288 DPI is safer than 300 DPI (assuming your monitor is 72DPI) because it maintains the original proportions for text. Does it make a difference?

p.s. I've posted this here because it is as much about resizing in Photoshop as it is Print Graphics, but feel free to move it.

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(Edited by SleepingWolf on 09-12-2009 18:09)

warjournal
Maniac (V) Mad Scientist

From:
Insane since: Aug 2000

IP logged posted posted 09-12-2009 22:03 Edit Quote

Seems to me that changing to Index Colour is a hack for Nearest Neighbor interpolation.

As far as 288 goes, it makes sense for perfect and even distribution, but I don't think a few extra lines to fill the gaps will be noticable. Each pixel will become a chunk of 4 pixels, but a sparse few will become a chunk of 5 pixels. Will anybody notice? Will it make a difference? I think negligable.

Not entirely sure about the text/font thing.

SleepingWolf
Paranoid (IV) Inmate

From:
Insane since: Jul 2006

IP logged posted posted 09-13-2009 18:19 Edit Quote

I'm going to some tests, on images with text, to see what works best.

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smathis
Obsessive-Compulsive (I) Inmate

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Insane since: Aug 2009

IP logged posted posted 09-13-2009 22:20 Edit Quote

Text falls in the same category of the pixel difference wj is speaking about. You'd wind up with a font 12.1pt or something similar, instead of 12pts. I am guessing if you're upsampling images from 72 dpi to 300 for print use, the person isn't going to be using an e scale so it won't matter.

SleepingWolf
Paranoid (IV) Inmate

From:
Insane since: Jul 2006

IP logged posted posted 09-14-2009 06:46 Edit Quote
quote:

smathis said:

Text falls in the same category of the pixel difference wj is speaking about. You'd wind up with a font 12.1pt or something similar, instead of 12pts. I am guessing if you're upsampling images from 72 dpi to 300 for print use, the person isn't going to be using an e scale so it won't matter.



Yes, I realize that a bitmap is a bitmap. I just want to ensure the text is still sharp playing with both variables:

1) Indexed color vs RGB

2) resampling at 300 vs 288 - this isn't just about font size scaling, it's also about the aspect ratio (height vs width).

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(Edited by SleepingWolf on 09-14-2009 06:47)

hyperbole
Paranoid (IV) Inmate

From: Madison, Indiana
Insane since: Aug 2000

IP logged posted posted 09-17-2009 17:18 Edit Quote

1) By using indexed colors, you are making sure that the colors in the image remain constant. When you scale the image in RGB mode, the scaling process can add more colors to your image as it tries to anti-alias the image while it scales. However, by converting the image to indexed first, you're fixing the colors that will be used in the image.

2) I don't think using 288 instead of 300 has anything to do with the aspect ration of the image or any text in the image. I think the statement that using 288 is safer because it maintains the proportions of the image is a mis-statement. However, as wj pointed out you will occasionally get blocks of five pixels instead of all blocks of four. This may not have any affect on the image unless you have sharp lines that are non-perpendiculat (vertical or horizontal). In that case, you will start to see jaggies in the lines because of the occasional odd size block of pixels. This will be more noticeable in images with text because text, more than most other types of images has lots of sharp lines at non-perpendicular angles. By using an integral multiple of the original resolution, you will reduce the amount of aliasing in your target image.

.



-- not necessarily stoned... just beautiful.

SleepingWolf
Paranoid (IV) Inmate

From:
Insane since: Jul 2006

IP logged posted posted 09-17-2009 17:50 Edit Quote

Hyperbole:
Thanks for the clarification on indexed colors.

I think you're right on DPI as well.

If you had a square image, you could imagine it as 288 x 288 i.e. just smaller than 300 x 300 - so indeed the quality should be the same IMO.

The aspect of the overall image obviously won't change unless you unchecked constrain proportions and resized.

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SleepingWolf
Paranoid (IV) Inmate

From:
Insane since: Jul 2006

IP logged posted posted 12-08-2009 19:38 Edit Quote

Just received a print on demand book which had screenshot tests.

I compared jpg vs png and can't see any discernible difference.

I compared 72 dpi vs 300 dpi (increased resolution with resampling unchecked) and again no discernible differences.

Bottom line: it seems jpg at 72 dpi gave excellent results.

Doing some research today, I came across this article. It contradicts about 99% of the info you will find out there.

http://www.adobepress.com/articles/article.asp?p=1374385&seqNum=4

Some interesting quotes:

quote:
The resolution setting of your monitor has no effect on the number of pixels captured in a screen capture.




quote:
Since it's been drilled into you that 300 ppi is the Holy Grail of image resolution, it's tempting to try to improve screen captures by increasing the resolution. Unfortunately, this usually makes them look worse by softening small details during interpolation.




quote:
If you do feel compelled to increase the resolution of a screen capture, there is an approach that may yield better results than resampling up to 300 ppi. In Photoshop, choose Image > Image Size, and then set the resolution to an even multiple of 72, such as 288 ppi. In that same dialog, set the Resample Image option to Nearest Neighbor . This avoids interpolation by simply repeating pixels rather than attempting to create pixels. It's not an appropriate approach when scaling images of a photographic nature, but it's a helpful solution for screen captures, because of their special nature.



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(Edited by SleepingWolf on 12-08-2009 20:17)

ouzhenyang
Obsessive-Compulsive (I) Inmate

From:
Insane since: Nov 2013

IP logged posted posted 11-20-2013 09:27 Edit Quote

edit tp: spam removed.

(Edited by Tyberius Prime on 11-20-2013 09:44)



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