Preview 'Actual Size' isn't working properly

Question

Preview 'Actual Size' isn't working properly

Hi

This is a long-standing minor irritation, but I would love to resolve it if possible. Preview opens an image and fits it to the screen size which is fine. If I then click Actual Size, it gives an image which is twice the actual size! I then have to do a single Zoom Out to get the real 'actual size' (which is still bigger than the fit-to-screen size).

This happens very often, but not every time (some images seem to work ok). Most images I work with are jpegs.

Anyone else notice this? Is there a solution?

iMac G5 17" 1.5Gb RAM, Mac OS X (10.4.9)

Posted on Oct 22, 2007 4:33 AM

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Answer 1

roam

Level 6

13,637 points

Oct 22, 2007 4:46 AM in response to christopher rigby1

Hi christopher

The term actual size can be confusing. Think of it as literal size.
The size the image displayed depends on both your screen resolution and the DPI (dots per inch) of the document or image being displayed.

Alter your screen resolution and observe how that affects the size of the displayed document when viewed at 'actual size'.

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Answer 2

Oct 22, 2007 5:12 AM in response to roam

I changed screen resolution to the next size down (from 1440 x 900 down to 1152 x 720). At this setting the image (which according to Photoshop is 864 x 1296 pixels, 72 ppi) in Preview Actual Size is a bit larger than Photoshop 100% - say about a quarter bigger.)

But that is not the screen resolution of my iMac. At the normal resolution of 1440 x 900, the problem is as I originally stated it. Because now, when I do Actual Size THEN Zoom Out, the Preview image is EXACTLY the same size as Photoshop 100%.

Preview should work according to my normal maximum screen resolution, surely?

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Answer 3

roam

Level 6

13,637 points

Oct 22, 2007 7:04 AM in response to christopher rigby1

I expect Photoshop is not displaying the image at 'actual size' rather it fits it to the window.
If you have a 17" monitor which is physically about 12.5" wide in reality and that screen's resolution is showing at 1440 pixels across, then an image that size (1296 X 864) displaying at 72 ppi would in reality (actual) be almost twice the size of the display. i.e 1440 / 72 = 20". You only have 12.5 of glass.

So Photoshop may show an image: correctly report it size in pixels at say 1296 X 864 but may reduce the size of the image to say 50% to fit it the window, and it may say 50% at the bottom of the window frame.

When you display it in Preview, it is too large, so zooming out, reduces it too say 50%, the same reduction that Photoshop is applying and they appear the same size. All the while, the image remains a 1296 X 864 unaltered, just that both applications are using the ppi as the determinate measure. If one was to increase the ppi the 'actual size' would become smaller.

note:
ppi pixels per inch
DPI dots per inch are the same thing.

Message was edited by: roam

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Answer 4

Oct 22, 2007 4:48 PM in response to roam

roam, I don't think you read my reply. You're talking about Photoshop 50%, and I did say Photoshop 100%. If you go back and re-read what I said, and then assume that I know the difference between Photoshop displaying at 50% to fit to screen, and Photoshop 100% (which is given at the top of the window anyway), then you will I hope appreciate what I'm talking about.

Photoshop 100% = Actual Size, ok? Preview Actual Size = twice that size. And that's what I'm reporting as the problem.

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Answer 5

roam

Level 6

13,637 points

Oct 22, 2007 5:05 PM in response to christopher rigby1

Ok, sorry I missed you stating it was at 100%.
I think the difference then is that Preview, which is a print application is displaying at the size that would be outputted from a printer, because that is its singular function, and so is showing you what things would look like at printer resolution of 72 ppi.

Photoshop is an image application, and is just showing the image at screen resolution.

If you take that image in Photoshop and select Print Preview from within the Photoshop application, does it say the image will need to be cropped/reduced?

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Answer 6

Oct 23, 2007 4:09 AM in response to roam

Right, ok. I've tried this again with a number of documents.

With a small document, resolution = 550 dpi, Preview Actual Size is really the actual size : it is very small on the screen and on the print preview. Correct.

With a resolution = 150 dpi, Preview Actual Size again shrank the image on the screen, this time to the size of a CD cover (which is what the image is). Correct.

With a resolution = 72 dpi (and 1600 x 1200 pixels, though that isn't relevant I believe) - Preview Actual Size is TWICE THE SIZE IT SHOULD BE. Problem.
By clicking Zoom Out, the image on screen shrinks by half, becomes the same size as Photoshop 100%, and is the correct actual size, and can be overlapped onto the Photoshop image seamlessly. THIS IS NOTHING TO DO WITH PRINTING. It's a display issue.

Now, this is not a 'feature' of Preview. It's EITHER a bug, OR it's a glitch in my computer. I suspect the former. It only seems to happen at 72 dpi. It is always with jpegs, but that may be because I have no other image types of that size and resolution.

Is there someone who has actually noticed this problem in Preview and can confirm that it does exist? And to make it ABSOLUTELY clear, I am NOT talking about the 'preview' that can be chosen when printing a document, I am talking about the APPLICATION Preview, the one with the dock icon that looks like a couple of photos with a jewellers loupe sitting on them, and with a menu bar that has Drawer, Rotate, Zoom etc.

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Answer 7

roam

Level 6

13,637 points

Oct 23, 2007 4:41 AM in response to christopher rigby1

What you report is normal.
An image at 150 dpi will display at half the size as one at 72 dpi or
72 dpi will display at twice the size of one that is 150 dpi (actually 144 is twice 72 but close enough)

_It is inverse._

I have already said this.

If one was to increase the ppi the 'actual size' would become smaller.

and the opposite also applies. They have an inverse relationship.

You are making the mistake of thinking that Preview is an image viewer.

I am NOT talking about the 'preview' that can be chosen when printing a document, I am talking about the APPLICATION Preview, the one with the dock icon that looks like a couple of photos with a jewellers loupe sitting on them, and with a menu bar that has Drawer, Rotate, Zoom

The Print Preview and the one in the Dock is one and the same. It is not an image viewer, that is just a feature. Preview is primarily a Printer Preview Utility. I have already said that. It can show documents and it can also show images.
Because it can show images you think it should be like an image viewer like Photoshop. It is a Print Preview application designed to show how an image will appear before it is sent to print.
The lower the DPI - the larger the actual size will be across your monitor's screen.
It works in DPI resolution to talk to the printer.
Photoshop works in absolute pixels X pixels to talk to the screen. They are doing two different things and you fail to see that. There is nothing wrong with your Preview application. Apple's Preview is the same thing as Photoshop's Print Preview.
Rather than lock on doggedly to your misconception, put it aside for a moment and take a fresh look.
I've done repeating myself.

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Answer 8

Oct 23, 2007 4:58 PM in response to christopher rigby1

Can someone else PLEASE step into this discussion. I can't get my point across to roam at all. He is failing to grasp what I'm saying.

I AM PERFECTLY WELL AWARE THAT DPI WILL ALTER THE RELATIVE SIZE OF THE IMAGE ON MY SCREEN. I am not some inexperienced newbie, I've worked with Photoshop on literally 000's of images.

I am EQUALLY well aware that a 72 dpi image will display and print at TWICE the size of a 150 dpi image. THAT IS NOT WHAT I AM TALKING ABOUT.

Rather me sticking doggedly to my views, will someone please read this thread from the beginning and understand once and for all what I am saying.

AT 72 DPI MY JPEG IN PREVIEW IS NOT - REPEAT NOT - DISPLAYING AT THE PRINT SIZE. IT IS DISPLAYING AT TWICE THE PRINT SIZE !! In other words at TWICE the size of Photoshop 100% which is the REAL actual size.

The final proof of what I am saying, is that at this "twice actual size" (what roam seems to think is the real print size) THE IMAGE IS PIXELLATED. Only a little but clear enough on high contrast edges: totally NOT present in Photoshop at 100% view, only visible in Photoshop at 200% view. The pixellation disappears when the Zoom Out button is clicked. Now there is NO WAY that a printable image is artificially pixellated - that is a clear sign that the image is being displayed LARGER than the actual, or print, size.

I think I've said it as far as I can now - could someone else PLEASE step in and advise? Many thanks in advance.

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Answer 9

Oct 23, 2007 5:36 PM in response to christopher rigby1

No, you are correct, it is annoying and no don't expect it to be fixed anytime soon. Preview is resolution independent unless you have Respect Image DPI for "Actual Size" selected. Either way the closest I get is 99% regardless of preferences and PDFs are the worst.

Sweet Polly

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Answer 10

imac007

Level 3

845 points

Oct 24, 2007 12:46 AM in response to christopher rigby1

Go to Preview>Preferences
Click on Images
Set the default image size.
Is the respect DPI check box for "Actual Size" checked?

By the way a picture displayed at 72 DPI is approximately 4x the size of the same picture displayed at 150 DPI.

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Answer 11

Oct 24, 2007 2:27 AM in response to christopher rigby1

sweetpolly, imac007 - thanks. Yes I have 'Respect DPI for Actual Size' checked.

I guess this is an irritation I'm going to have to live with. Preview - despite what was said above - is as much an image viewer as it is a print preview, I just think a bit more thought should have been put into how large low-res images were going to be displayed. And I think displaying such images at twice Actual Size (or print size) IS a bug.

imac007 - yes I realise that if you half the resolution you end up with 4 times the area. When I said 'twice the size' above, I was really meaning linear measurements (length, height) rather than area.

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