Any time I save a file, I always choose 100% for quality.
I’ve heard that every time an image is opened and re-saved, there is loss. But if I choose 100% every time, is there significant loss?
A good reason for asking is photos that were taken with the camera sideways. I’d like to go through the photo folder and turn them all the right way.
Another example is red eye removal. I like to go through all my pics that need this.
Another example is resizing pics for printing. I like to use Photoshop Album to crop my pics to the appropriate print size all at once…then open them with The Gimp.
But if I open up the pics, make those changes, and resave…am I losing data?
I never work with the originals. If I’m going to put pics on the web, share them with friends, or print them, I do all my image correction each time. I try to leave my originals as intact as possible. But do I have to go nuts about it?
Technically speaking you are losing information when you take raster image data and save it as a JPEG. It is best to keep images in a lossless format while working on them and save as a jpeg as the last step. Rotation in some cases will also cause information loss. This happens because most cameras downsample their jpegs to save space. What that means is that (in case of YUV422) each two pixels have two “luminance” values but share a “chrominance” value. This is done two horizontal neighbors, so when you rotate and save as YUV422 again you will lose some color information.
Another issue with resaving as JPEG is that while your camera will use one set of quantization tables, your imaging software can very well be using it’s own set. This can lead to some weird lossiness that would not occur if you consistently use the same application to resave.
However, your question doesn’t really make that much sense, if you’re already keeping the originals, just check how many saves/operations/resaves will make the quality unacceptable and extrapolate from there. Quality is very subjective and what I find acceptable might seem horrible to others.
You might want to consider using a non-destructive editing program like Google’s Picasa. It can do redeyes, rotations, crops, resizes, etc. all without modifying the original. It remembers what you did to the pictures (and shows you live previews) but only exports to JPEG as the very last step.
Don’t all major editing programs (PhotoShop, Gimp) do that? The only time things are a problem is when you save in JPG format. They all use the lossless format provided by the programs and only save JPG at the last step.
No, most editing programs save to the image directly. Picasa never touches the original image. When you “save” an image, Picasa actually just records the actions you performed into a separate text file. Then, based on that text file, it’ll create a new JPEG on demand.
(It does this invisibly in the background – Picasa remembers what every image is SUPPOSED to look like based on that text file and it always shows you an up-to-date preview, but it doesn’t actually generate a JPEG until you export. Meanwhile, the original file is never touched.)
I don’t know about most, but two data points are: Photoshop Elements (and its obscure predecessor, whose name escapes me) saves in its own proprietary format, and ThumbsPlus saves in the original file.
I meant that I like to do the types of corrections that will never change, such as red eye reduction or rotation.
Image quality correction with levels, curves, unsharp mask, etc. I never do to originals.
Someone mentioned using formats without loss; The Gimp has its own format for this; I can see how if a picture is a long project I’d want to do that. But I do all the corrections on the pic at once before printing.
Both of those save the resultant image, possibly lossless, and possibly with history of operations. They do not save the original + a set of operations like Picasa.
Other applications that do this, too, include Apple’s Aperture andAdobe Lightroom. Both are currently only available for Mac. Adobe Lightroom is still in beta, but a fully functional version. Both programs are aimed more at professional users, but if you have a Macintosh, I urge you to give at least Lightroom a shot. A PC beta will be out soon, and the betas are fully functional until the official public release (well, the current beta is valid until June, but I expect there to be at least one more beta before Lightroom hits the shelves.)
No image editor modifys the original until you do a “Save” to the original file name. Anyone that works with images much always saves modified images to a new file name thereby keeping originals intact. I can’t think of any reason that it would ever be necessary to do multiple “Save” of an image. If you open an original and create a new image from it and still have the original open, then simply close it without saving it and you won’t recompress it. You don’t need to run the “Save” process simply to put away an image that is open in the editor.
No you don’t. But some people take an original, do some tweaking, and then save it. Then they open up the saved file, realize they missed a couple of things, and then save that. Then they open it up again, and say, hey, maybe the color balance is a little too blue, let’s warm it up a bit…etc…degrading their JPEGs along the way. With TIFFs or PSDs I would routinely do something like that. With JPEGs, I would always have to go back to the original and recreate the sequence of changes I’ve made in order for them to look optimal. Most of the time, though, I just got lazy and added further changes on top of the JPEG (which is already one or two saves removed from the original).