Major Quality loss when editing in Iphoto 09

Cropping is the process of throwing part of the photo away - this, of course, reduces the total information available and reduces the quality -- physics dictates that when you throw part of something away what is left is smaller that it was before you threw part of it away

for a 300 dpi 20x30 print you need roughly 3600x2400 pixels - for a 150 DPI print (the lowest most people consider acceptable quality) you need 1800x1200 -- if you crop to smaller than that you will have noticeably reduced quality

LN

iPhoto doesn't "take" your quality. What's happening is that your 10 MB RAW file is being saved as a jpeg. As jpegs are lossy the file is a lot smaller than the RAW. This will happen no matter what app you use to process your RAWs.

Have a look at the Help on RAW. It explains it quite well. A RAW is a camera sensor dump. You can't do anything with a RAW - can't print it, use it in a Slideshow, show it online etc. SO you need to process it to a usable form. This can be either a lossy jpeg or a lossless Tiff.

Regards

TD

Of course. Every time you save a jpeg there is further data thrown away. It's in the nature of jpegs. However with iPhoto's _[Non-Destructive Editing Feature|http://docs.info.apple.com/article.html?path=iPhoto/7.0/en/11464.html]_ the impact is minimised so that you never lose more than a single generation.

As a point of comparison, Old Toad once compared iPhoto's compression algorithm with Photoshop's and found it to be about the 8 point on the scale of 12.

Regards

TD

Try make the same edit in another app. Compare the results.

Regards

TD

Welcome to the Apple Discussions.

the only difference is that Iphoto took my quality !!

Are you basing the "quality" loss on visual appearance of the photo or on the resulting size of the jpeg file? If it's the latter that is really not an accurate method. True, some information is lost with a jpeg edit and save (only the first edit in iPhoto results in additional jpeg compression) but, in my experience, you would have to print a VERY large print before seeing any noticeable image degradation. I've compressed jpegs as high as 60%, i.e. a quality setting of 40, and for most all uses up to 5x7 prints haven't seen noticeable image degradation. However, I realize image quality is subjective and open to individual interpretation.

So unless you are visibly seeing image degradation I wouldn't worry about the file size reduction, especially in iPhoto as it's compressed only once no matter how many edits are made and saved. Apple uses a compression algorithm that gives the best image quality for the amount of compression it uses.

The following is from the Usernet FAQ site article "JPEG image compression FAQ, part 1/2':

Subject: [4] How well does JPEG compress images?

Very well indeed, when working with its intended type of image (photographs and suchlike). For full-color images, the uncompressed data is normally 24 bits/pixel. The best known lossless compression methods can compress such data about 2:1 on average. JPEG can typically achieve 10:1 to 20:1 compression without visible loss, bringing the effective storage requirement down to 1 to 2 bits/pixel. 30:1 to 50:1 compression is possible with small to moderate defects, while for very-low-quality purposes such as previews or archive indexes, 100:1 compression is quite feasible. An image compressed 100:1 with JPEG takes up the same space as a full-color one-tenth-scale thumbnail image, yet it retains much more detail than such a thumbnail.

Read more: http://www.faqs.org/faqs/jpeg-faq/part1/#ixzz0UKB59gND

Message was edited by: Old Toad

Any word on the update yet?