View Full Version : photoshop zoom/accuracy question

02 February 2008, 03:51 PM
My apologies if this has already been answered somewhere else, but I can't find it -

I do most of my Photoshop painting at 300 dpi, usually 3000-4000 pixels wide/high. When I look at things at 100% or larger they look fine. When I zoom out to something like say, 66% or 33%, they look off - particularly the detail on human faces. Eyes seem a little crooked, features not quite symmetrical, things like that. And I find that if I resize my image down to a smaller size, say 72 dpi, 1200x1200, these inaccuracies seem to follow through, though to a lesser extent that with the zoom out - I assume because some antialiasing is happening with the resizing that doesn't happen with the zoom?

So my major concern - why does everything look right at 100%, and wrong when the image is smaller? Is this some sort of optical illusion, or are my details painted at 100% truly inaccurate? Should I be working at 50% (ouch) instead?

02 February 2008, 04:39 PM
I think this is simply a screen aliasing effect, where at 33% it is showing 33.333... percent of the pixels in your image and so jumps 1 every so often as it cannot display 1/3rd of a pixel. Values which go into 100 without a fraction of a pixel should display more accurately (25%, 50%, 75%, 200% etc) though annoyingly these are not the 'click-zoom' defaults.

Also, i don't think altering the DPI of your image will have any effect at all. DPI, as far as i'm aware is a measure of print resolution, and is simply used by Photoshop to determine the print size of your document. eg. 3000px wide @ 300 dpi will print 10 inches. Your monitor will display at whatever resolution you have it set to.
Monitors tend to display at 96dpi (i like to think of it as pixels per inch rather than dots), so a scanned 5"x7" photo @ 96dpi should display at around 5"x7" on your screen when at 100%. Though working at 96dpi is relatively pointless. 300dpi is pretty standard photographic print res, so stick with that.

02 February 2008, 10:44 AM
You can be confident that what you are seeing when zoomed to 100% is accurate. This is also the detail you'll get when you print. When a more 'fit screen' view is required, photoshop has 2 and sometimes three (tool dependent) zoom percent boxes which can be typed into, I find this to be fairly quick to get to 25/50/75% which suffer the least from aliasing artifacts, I suppose an action button could be made for those as well. It can be helpful to view an image at actual print size as well, but PS needs to be told how to do it: create a new document 1 inch by 1 inch, for example default dpi is fine. Turn on the rulers if you like. Under the view menu choose View/Print Size. Measure the resultant document size with a physical ruler. It'll be wrong inevitably. Edit preferences/Units and Rulers and change the New Document Preset Resolution to be roughly 15 higher or lower to get a feel. Choose View/Print Size again and watch as you creep up on the correct value for your screen. After a few trials you'll have a working print size preview.

02 February 2008, 03:59 PM
Thanks for the replies, that all makes perfect sense! I'm glad to know that what I'm seeing at 100% is indeed accurate, that helps a lot.

03 March 2008, 03:36 AM
If you want an accurate look, zoom in even multiples of 100 i.e. 200%. 300% or 50%. I can't remember the exact reason for this but I believe it is because if you zoom in like 66% it can't accurately make the pixesl 2/3 the size but it can make them twice or 3 times or half the size without a problem.

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03 March 2008, 03:36 AM
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