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sixtus
01-19-2007, 01:03 AM
Hi there.
I would want to know why, after a whichever 300 dpi photo image modification, iPhoto always changes the resolution from 300dpi to 72dpi.
To notice that X, Y dimensions (mm or cm) of the modified image are multiplied x 4,16; that is the number of pixel remains the same ones.

sixtus

Boots
01-20-2007, 05:49 PM
Sounds like it is scaling the image.

What happens when you export (a copy of) the image? Is the copy 300dpi?

sixtus
01-21-2007, 02:34 AM
Hi Boots,
All images are in JPG format and after iPhoto modifications are scaled in dimensions (cm) but not in pixels which remains the same.
Exporting it in Photoshop it remains at 72 dpi.

That means :
- original image : 300 dpi, 3872 x 2592 pixels, 32.78 x 21.95 cm.
- after any iPhoto modification, 72 dpi and 3872 x 2592 pixels, 136.6 x 91.44 cm
With Photoshop:
1) after a modify 72 dpi to 300 dpi, the image is 16133 x 10800 pixels but dimensions remains 136.6 x 91.44 cm
2) after a successive pixel modifications from 16133 x 10800 to 3872 x 2592 the resulting image seems as the original, but I think degraded in quality.
What's Your opinion ?

Best

kaye
01-21-2007, 08:39 AM
I could be missing something here but I exported two jpg scans and two digital photos from iPhoto to the desktop. One of the scans was at 150dpi and in Pshop CS2 it remained at 150ppi. The other scan was at 300 and it remained at 300ppi in Pshop.

The digital photos, one at 180 and one (from a friend's camera) at 300. Both photos in Pshop retained their resolution. It seems as if somehow you are exporting from iPhoto either with the wrong settings or a thumbnail is being exported (less likely IMHO).

I can take a screenshot of the iPhoto export window settings if that would help. k

sixtus
01-22-2007, 01:55 AM
Hi,
Have you modified, with iPhoto, your images before to export them ? Because the problem happens only and only if, I modify my images (digital photos or scanned images) with iPhoto v.6.0.5 (316)

Best

kaye
01-22-2007, 06:43 AM
sixtus,

The only modification done to this image or any others I would do is Enhance in the Toolbar. If I want to do any more mods, I go to Pshop CS2. I am using iPhoto v.6.0.5 (316), same as you.

Here is what my iPhoto Export window looks like:
http://homepage.mac.com/kaye_yum/.Public/iPhotoExport.jpg

And here is what Pshop Image Size looks like:
http://homepage.mac.com/kaye_yum/.Public/PshopImageSize.jpg

Does that shed any light on the issue? k

Boots
01-22-2007, 07:07 AM
Did some research and I'll get back shortly on this....later today.

sixtus
01-22-2007, 12:36 PM
Thanks Boots,
I don't use Export menu function, but I use image controls panel tools to modify some and then I use the the contestual menu "edit wit external editor.." to open the, just modified, image with Photoshop.

Read You later.
Sixtus

Boots
01-22-2007, 01:23 PM
Hi sixtus,

Like you and kaye, I use (occaisionally) iPhoto v. 6.0.5 (316).

What I discovered thus far:

1. As far as I can tell, iPhoto displays only the pixel dimensions in the Information pane of the iPhoto browser window. For me, it does not display the resolution or dimmensions in inches or cm. Where are you getting the print dimensions?

2. As far as I can tell, in iPhoto, a photo can be resized only by either:

a) cropping in Edit mode which subtracts pixels or
b) "scaling" in the "Export Images" dialog.

"Scaling" in iPhoto is funky; it appears to actually resample (subtracting pixels)when decreasing the pixel dimensions in the "Scale images no larger than: ____ x ____" dialog to less pixels than the original. Putting in larger values than the original seems to have no effect- the image is not scaled or resampled either way.

Like kaye- when I open in Photoshop an image "scaled down" in iPhoto, the pixel dimensions are reduced but the ppi are the same.

"Scaling" is really supposed to mean reducing the ppi as you increase the print dimensions or increasing the ppi as you reduce the print dimensions. The number of pixels remains the same but their individual size changes.

"Resampling" is supposed to mean either adding or taking away pixels and either keeping the print size the same or changing it in the process.

iPhoto appears to be resampling when reducing the pixel dimensions and maintaining the same ppi.

The only way I can resample up or scale up through iPhoto is in the iPhoto section of the print dialog if I send the file to the print driver. But I don't know whether is is truly scaling or resampling- I'd have to print test sheets. As I understand it- it really is the Mac OSX pdf engine doing all that conversion anyway.


Hi Boots,
All images are in JPG format and after iPhoto modifications are scaled in dimensions (cm) but not in pixels which remains the same.
Exporting it in Photoshop it remains at 72 dpi.

That seems to be what I'm seeing too- except that the "scaling" is really only one way: down. And with the ppi remaining the same, that means resampling, not scaling.


That means :
- original image : 300 dpi, 3872 x 2592 pixels, 32.78 x 21.95 cm.
- after any iPhoto modification, 72 dpi and 3872 x 2592 pixels, 136.6 x 91.44 cm

That sounds like the true definition of scaling.


With Photoshop:
1) after a modify 72 dpi to 300 dpi, the image is 16133 x 10800 pixels but dimensions remains 136.6 x 91.44 cm

That is exactly as it should be, a resampling up (adding pixels)


2) after a successive pixel modifications from 16133 x 10800 to 3872 x 2592 the resulting image seems as the original, but I think degraded in quality.

This is because in #1 you are adding pixels (upsampling), but not adding any new detail or information. In the process you are altering all of the original pixels. The result is usually soft. Then in #2 you are subtracting pixels (downsampling) and subdividing that entirely *new* image using 1 pixel to decscribe what was previously described by 4 pixels...

Not only that- when you modify a jpeg image, each time you save the change you degrade the image even more. Best to work on a psd or tiff and when finished making changes, Save As a jpeg or save a re-sized copy as a jpeg. Downsampling is much preferred over upsampling; start large and make smaller copies of a large original.

sixtus
01-23-2007, 01:18 AM
Where are you getting the print dimensions?

in Photoshop "Image Size ---> Document size" : I've verified that document size may be equivalent to print size.

An other little information, I have never modified dimensions or resolution with iPhoto; I use it only for minor chromatic (exposition, white balancing, gamma control etc,) corrections. After these corrections types I have found the resolution modification from 300 to 72 ppi (ex dpi).

Sixtus

Boots
01-23-2007, 07:37 AM
I just tried that with a 300ppi image, and sure enough- same results as you:
after an adjustment- in this case, a minor retouching- is made in iPhoto, and the pic is then opened in Photoshop via "open in external editor"- it is now 72ppi and scaled in print dimensions accordingly!

This seems like completely arbitrary and unexpected behavior on the part of iPhoto. :confused:

For one thing- 72ppi is in this day and age, decidedly not an accurate representation of typical screen resolutions. For instance, my ACD has a screen resolution of about 101.5 ppi, and most other monitors have similar variations from the old Apple screens which were- back in the day- actually 72ppi.

sixtus
01-23-2007, 11:34 AM
...and then sic stantibus rebus, what can I do? Some time ago, I have sended the question to Apple too, but no answers at all (of course).

Hoping for a new iPhoto update I thank You, for your availability in trying to understand the problem.

P.S. What application You use to catalog digital photos or generic digital images, instead of iPhoto ?

Thanks again
Sixtus :)

Boots
01-23-2007, 12:41 PM
What application You use to catalog digital photos or generic digital images, instead of iPhoto ?

I use Bridge (part of Photoshop CS2) or the File Browser in Photoshop CS- as well as the stand-alone app iViewMediaPro which is pretty robust these days.

For me, iPhoto is most advantageous for the built in scripting in conjunction with .Mac, the photo albums, and iWeb. But for any serious editing, I use Photoshop.

sixtus
01-24-2007, 01:13 AM
Hi Boots,
thanks again.

sixtus

sixtus
02-18-2007, 01:40 PM
Hi Boots,
After whichever Photoshop modification to any D80 digital JPEG photo, iPhoto miserably and systematically crash with corruption of the com.apple.iPhoto.plist preferences file.

I hope for Life 07 to solve the problem otherwise I will opt for the Aperture purchase.

Ciao
Sixtus

:(

Macaholic
02-18-2007, 09:39 PM
My 2 cents,
No Iphoto here, I use Graphic Converter and Photoshop.
I can not say enough good things about Graphic Converter.
This is my defalt app for opening images
I've used it for years and it keeps getting better.
http://www.lemkesoft.com/
Used in conjunction with photoshop= Awesome!

Dave