iPhoto Exporting Quality Size dpi etc. etc. Confused?

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Mr..E Author

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iPhoto Exporting Quality Size dpi etc. etc. Confused?

Life used to be simple!

JPEG Quality:

If I wanted a photo for view on the web or my computer screen, I wanted a resolution of 72dpi (dots per inch)

If I wanted to it professionally printed, I wanted a resolution of 300dpi, and if I wanted a rough print version for

my home/business printer then I would probably be OK with 150dpi.

Now I can export from iPhoto as JPEG and I am no longer given the resolution options (72 or 150 or 300dpi etc.)

but rather the options for JPEG Quality ARE: Maximimum, High, Medium and Low [unhelpfully referred to as "Smallest size" what else would it be?]

Whatever choice I make appears to make no difference to the visual quality of the picture on screen, but makes a heck of a

difference to the file size AND gives me NO help on what the resolution of the resulting picture is.

0. This would lead me to believe that I should choose Low for ALL web or computer screen uses - as this will result in the

smallest possible file size - which in turn will reduce loading speeds for websites. Is this correct?

Unhelpfully, the iphoto Manual does not explain what these Quality Options mean and therefore I have no idea why or when I should

choose one over another.

1. Can someone out there who really knows their stuff, demystify this for me ?

What do these Quality Options mean, what dpi is assigned to each, and why and when should I coose one over another?

Maximimum

High

Medium

Low

JPEG Size:

This is confusing. If I know that for a particular use I need a particular size photograph (height vs width), I edit it in

iPhoto to the height/width that I need. For example, in the gallery I am using in Rapid Weaver, the designer suggests

a good size for one particular design's revolving banner photos is 980 wide by 656 high - and I am assuming that these are pixel dimensions.

My photos from various sources are inevitably greater than this - and in some cases I might want to re-frame a portrait

photo into a landscape shape. To do this I use the Edit and Crop facility in iPhoto. And I make sure that the photo is edited to

the dimensions I want first.

iPhoto retains the full size photo in it's library, and I can always get it back after cropping if I wish

(by duplicating and reverting to origonal). However once cropped, it helpfully appears to EXPORT the cropped size.

The EXPORT function allows me to chose a JPEG's Size (by which I assume it means pixel width vs height)

2. Can someone tell me the exact effect/meaning of choosing any one of the following - in other words what do these mean or

put another way what pixel size am I choosing for:

Small

Medium

Large

Full Size

3. And am I choosing just the Height size or the Width size and what happens to the other dimension? And how does it

decide? And what are the Heigh or Width sizes allocated to these rather odd choices (Small, Medium, Large, Full Size.)

4. I am assuming that Small must equal a specific Width for a landscape photo, and in that case does it keep the height as it was, or does it constrain the proportions on the basis of the Width it has allocated to Small?

There is a fifth option, but again, it is unclear as to what exactly it does, and I would like help here too! (Sorry, but this is driving me demented!)

Custom

Within Custom, I have three choices:

Width

Height

Dimensions

5. What happens to the Height if I define the Width option? Or similiarly, what happens to the Width if I define the Height option?

6. What on earth does Dimensions mean when it only gives me one dimension to define?

Will it try and make a portrait picture square for example? Is it editing here?

Sorry this is so long, but I would really like to NAIL this - and I suspect I am not the only one! 🙂

All I am trying to do is to create the optimized output for the purpose I intend to use a picture for - really simple - or is it?

Thanks to anyone who can have a go at this..... Michael

MacBook Pro, Mac OS X (10.7.5)

Posted on Apr 22, 2013 3:18 AM

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Answer 1

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Mr..E Author

Level 1

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Apr 22, 2013 4:24 AM in response to Mr..E

Mr..E wrote:

Life used to be simple!

JPEG Quality:

If I wanted a photo for view on the web or my computer screen, I wanted a resolution of 72dpi (dots per inch)

If I wanted to it professionally printed, I wanted a resolution of 300dpi, and if I wanted a rough print version for

my home/business printer then I would probably be OK with 150dpi.

OK Having trawled through a series of earleir posts, I have discovered the error of my outdated thinking on dpi and the de-mystification comes from Old Toad here:

The Myth of DPI.

Thanks a bunch for that.

However, the rest of my questions (now without the context of dpi) are still valid.

The purpose of my understanding what these options mean is ultimately for me to be able to have a simple way of choosing the Quality Option for a JPEG in conjunction with the Size Option.

For example if I can decide that by choosing to size a photo in iPhoto by cropping it means that the Option I should choose within the Export Window for Size is: Full Size, then that makes life easy for me. However, I still don't have a way of deciding which Quality to choose.

I understand that the Quality has to do with compression, but to optimize output for print (where size of file is of no importance to me) do I always choose Maximum? [I expect so?]

And if I want to embedd a photo in a .pdf for view and possible download from a website (where the person downloading can choose to print the .pdf with the photo in it), do I choose High or do I chose Medium? (Here I will want to reduce the file size as much as possible of the .pdf, obviously, but my customers may want to print it our from their computer(s)).

And if I just want to have the photo on a website, do I always choose Low? (Here I want my file size to be as small as possible).

Hope that clarifies ........ Thanks for any help you can give me..... 🙂

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Answer 2

Yer_Man

Level 10

162,308 points

Apr 22, 2013 5:08 AM in response to Mr..E

This is quite simple, but the problem is you are confusing Jpeg Quality and DPI, they are unrelated. You're confusing cropping (which fixes the shape) with setting the dimensions (which sets the length by breadth), which, while related, are not the same thing.

Jpeg quality has nothing to do with DPI. It's all about the amount of compression applied to the image on export. So, you have have a 300 dpi image at low quality and one at high quality. It has nothing to do with dpi.

If I know that for a particular use I need a particular size photograph (height vs width), I edit it in

iPhoto to the height/width that I need.

No you don't. You can crop it to a particular aspect ratio - or shape - but not to size. 6 x 4 is the shape, not the size. Note the absence of inches or cm or meters there.

The only way to set the size - that is dimensions - is by exporting and making your choices under the size. That sets the length by breadth of the image.

Under Size, Full Size is exactly that: the image at the dimensions imported from the camera. The others allow you to scale the image. Each reduces the size by about 33% or thereabouts.

The options under Custom allow you to set the exact dimensions of the exported image. If you choose, say, 400 pixels as the height, and if the image is cropped to 6 x 4, then the resulting image will be 400 x 600 pixels.

So, if you define the height, the app will calculate the width based on the aspect ratio or shape. And so on. Dimension means you can set the longest side... handy if you're exporting a mix of landscape and portrait images.

but to optimize output for print (where size of file is of no importance to me) do I always choose Maximum? [I expect so?]

There is no right answer to that question. The quality of the printed image is much more dependent on the sharpness and colour saturation of the image than the file size. Put it this way, a good sharp image will print well at a small file size. A fuzzy one will print fuzzy at any size. I would use maximum for archiving and if the images are going to be edited further as Jpeg is a lossy format.

Yes you can choose the quality if you choose full size.

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Answer 3

Mr..E Author

Level 1

0 points

Apr 22, 2013 11:56 AM in response to Mr..E

Terence, thank you very much for your excellent reply. I don't know if anyone pays you for all this guidance, but given your assistance to the community, you certainly deserve to be.

I also found one of your Tips by clicking on your Name (Terence Devlin) and taking a look at an obvious post on the subject you have made previously. There I found this: https://discussions.apple.com/docs/DOC-4921 And if anyone wants a more in-depth explanation than the one in this post, this is a place to check out.

Ok so my learning!

1. I now understand Aspect Ratio 😀

2. I now know how to change the Dimensions (Size) of my image 😀

3. I understand that Quality has to do with Compressions, but ... 😕

So to clarify, on the Dimensions front, you said:

"Under Size, Full Size is exactly that: the image at the dimensions imported from the camera. The others allow you to scale the image. Each reduces the size by about 33% or thereabouts."

Assuming my math is correct does this mean:

Full Size = 100% of the Imported from the camera Dimensions

Large = 66% of the imported Dimensions

Medium = 44% of the imported Dimensions

Small = 29% of the imported Dimensions

Finally, is there a way of knowing or deciding how much compressions to use in the choice of Quality?

Maximimum

High

Medium

Low

Can you say something about that or direct me to where you have already covered it!

I really do appreciate your support - thanks....... Michael

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Answer 4

Yer_Man

Level 10

162,308 points

Apr 22, 2013 12:17 PM in response to Mr..E

On the dimensions:

It's biased towards medium to large images. You can see why. Very few people will want to export a 100 px image unless they're maing thumbnails for a web page, and if they are then there the kinds of folks that will know how to use the custom setting. I reduced a 3000 x 2000 (approx) image to 640 x 480 with the medium setting.

On compression...

Depends on what you're using the image for... Web site? Start at Low and work from there if the quality is poor. Archiving as I said above: I'd go for max. The rest - trial and error...

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Answer 5

Mr..E Author

Level 1

0 points

Apr 23, 2013 1:03 AM in response to Yer_Man

OK I've got it! - Thanks a thousand - and for anyone who wants a Quick Summary, here it is:

1. Cropping a photo in iPhoto sets the Aspect Ratio

Despite what it appears to do, cropping a photo in iPhoto does not affect the photos’s height or width. It does affect it’s Aspect Ratio - or shape (for example 6 x 4 ), and what is visible within that shape - but not the width or height. Note the absence of inches or cm or meters there. It also affects the content of the picture - or rather which area of the picture is visible (which is the ‘cropped’ area).

So it is OK to Crop the photo in iPhoto, but this should not be confused with the idea that you are cutting the photo into a specific dimension (width or height) - to do that you need the Export facility in iPhoto where you choose a JPEGs Size.

2. JPEG Size

Once the Aspect Ratio is determined (the shape) of the visible area of the picture - the Custom Size Option in the Export Facility can be used to select either the Width or the Height. Obviously if you chose the width, then that measurement will pre-determine the height as iPhoto will calculate the height needed to retain the Aspect Ratio you have set when you cropped it.

If you don’t crop, it will calculate based on the initial Aspect Ratio (shape) of the original photo.

Full Size is exactly that: the image at the dimensions imported from the camera. The others allow you to scale the image. Each reduces the size by about 33% or thereabouts.

Full Size = 100% of the Imported from the camera Dimensions

Large = 66% of the imported Dimensions

Medium = 44% of the imported Dimensions

Small = 29% of the imported Dimensions

As a rule of thumb a 3000 x 2000 (approx) image will reduce to 640 x 480 with the Medium setting

Thumbnails can be generated using the Export and then Web Page function, rather than the File Export function.

Otherwise, you can use the Custom setting to specify an Exact width or an Exact height (and of course the Aspect Ratio will determine the other dimension NOT specified.)

3. JPEG Quality

JPEG Quality is setting the compression of the file which will affect the file size (not the picture Dimensions or the Aspect Ratio), but it will also affect the Quality of the visual image. So here you are seeking to minimise the file size while not losing acceptable visual quality.

Which you choose depends on what you're using the image for... Web site? Start at Low and work from there, if the quality is poor or visually unacceptable, choose a higher quality.

If you are Archiving go for max. The rest - trial and error...

4. For a deeper understanding of these issues

1. Read the thread below AND/OR

2. Take a look at this: The Myth of DPI. AND

3. This: https://discussions.apple.com/docs/DOC-4921

Clarity Rules! - And many many thanks to Terence Devlin for the lesson...

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