Compresssing jpeg file iMac Lion

[Bob5545]

I have several jpeg files I want to reduce in size email. They are scanned and each is about 2.4 MB in size. When I right click to compress it does not shrink the file. The new jpeg.zip is the same size as the original. Why is this file not compressing to email?

Other than Colorsync is there an easy way to zip these files as part of Lion.

Thanks

[DeltaMac]

A .jpeg file is, by definition, already a compressed, lossy format. There's often very little size reduction if you make a .zip file - because there's not much to compress (and maintain the same quality image)
You can open with your Preview app (or some other graphics file app), and export as a smaller file (which means the result is smaller, but lower quality). You can adjust the file size to tradeoff file size against desired quality of the image.

[trevor]

For taking a .jpeg and compressing it further, my tool of choice is GraphicConvertor. It also does millions of other things really well.

Trevor

[NaOH]

Quote: Originally Posted by DeltaMac You can open with your Preview app (or some other graphics file app), and export as a smaller file (which means the result is smaller, but lower quality).

Similarly, after adding an image to a Mail message, at the bottom right of the window is an Image Size pop-up menu which will usually offer four options: small, medium, large, and actual size. I prefer this method simply because it's faster.

[acme.mail.order]

2.4Mb is a reasonable size for an email attachment.

Every method above is standard practice, but will lose a substantial amount of quality. If you need the original quality you will have to use something other than email, like DropBox.

[mnewman]

Quote: Originally Posted by trevor For taking a .jpeg and compressing it further, my tool of choice is GraphicConvertor. It also does millions of other things really well.

+1

Great tool and it gives you many options for re-compressing JPEGs.

You may find that you can get a substantial reduction in file size without much loss of visible quality.

[chabig]

You don't "recompress" JPEGs to make them smaller. You throw away resolution to make them smaller. That's why graphics programs can export smaller version and compression programs can't.

[mnewman]

Sorry. Stupid me again.

[ricede]

Providing that the person receiving the emails doesn't want to blow the jpeg pics up - i always open the pic full screen on my 17" MBP ( which does have a high definition screen )and take a jpeg screenshot of it. This allows me to send a large pic at a small size. Ok its not the original but its very similar, and the size drop is enormous.

[vanakaru]

I use Photoshop ”Save for web”. Have not find anything to beat this. Image size max 1200px JPG quality 50. Looks great and the file size is about 300kb.
However it may be stupid to get PS for this task only. But free app GIMP should have save for web option too. And I recommend to work on the pix you posting always. For me it would be unacceptable to receive JPG with email large than 500kb.

[benwiggy]

Quote: Originally Posted by NaOH Similarly, after adding an image to a Mail message, at the bottom right of the window is an Image Size pop-up menu which will usually offer four options: small, medium, large, and actual size. I prefer this method simply because it's faster.

I concur. Easy and simple. However, the following occurs to me:

1. 2.4Mb is well within email's capabilities. Between 7 and 10 Mb is the normal limit, unless you're both using Gmail or something with known attachment size abilities.

2. You can either make a JPEG image smaller in size, or you can make it have more compression. (Or both.) More compression makes it blotchier and loses detail, resulting in the well-known "Jpeggy" blotchiness. Reducing size just makes it smaller. Obviously, if you try to display a smaller image at a larger size, you will see a more pixelated image (slightly different from jpeg blotchiness!)

3. Zipping files (i.e. Compressing in the Finder) is a lossless form of compression. It doesn't throw away data. Consequently, if data is already heavily compressing (JPEGs, PDFs, etc), then zipping won't have much to work with and won't reduce the file size by much. If any.

[ricede]

Quote: Originally Posted by vanakaru I use Photoshop ”Save for web”. Have not find anything to beat this.

i always vaguely wondered what that was. I don't do web work so never bothered to find out.

I just tried it out & yes its brilliant. A bit more work than a screenshot, the size comes out roughly the same but the definition is way better.

Thanks vanakaru - always great to learn a new way to do something.

[acme.mail.order]

The "Save for Web" export in most image editors also strips out various comments, EXIF data (like where you were standing when you took the photo with your GPS-equipped camera) and preview icons. This means you can increase quality and keep the same file size.

[NovaScotian]

Quote: Originally Posted by mnewman +1 Great tool and it gives you many options for re-compressing JPEGs. You may find that you can get a substantial reduction in file size without much loss of visible quality.

And, when you choose to compress it, GraphicConverter gives you a thumbnail of what the result will look like so you're not shooting in the dark.

[trevor]

Quote: Originally Posted by chabig You don't "recompress" JPEGs to make them smaller. You throw away resolution to make them smaller. That's why graphics programs can export smaller version and compression programs can't.

Well, I don't want to argue semantics, but you certainly can recompress JPEGs to make their file size smaller.

Resolution is the pixel dimensions of an image, like 1024 x 768 for example. One way to make the file size smaller, of course, is to make the resolution smaller. So for example you could take a 1024 x 768 image and 'throw away' resolution to make it 800 x 600. That works, but is very unsatisfying--the whole image is smaller.

A much smarter way to make the file size smaller is to recompress it. For example, use GraphicConvertor to increase the compression on the JPEG. Doing this will NOT make the image size smaller, but when used properly (GraphicConvertor lets you play with a slider to change the compression while viewing a blowup of the image, so you can watch for JPEG artifacts and stop or reverse your slider movement when artifacts become obvious) you can make the file size smaller without any obvious change to the quality.

(Of course, there is a reduction in quality when recompressing a file to make it smaller, but it can be done so that the reduction in quality is not obvious, or even visible at all to non-professionals.)

Trevor

[acme.mail.order]

Well, if you want to quibble about semantics, ANY manipulation of a jpeg image* involves re-compressing it - the editor works on a raw data level and runs the jpeg compression routine again when you select "Save".

* In case anyone doesn't know, geometric manipulation such as rotate, flip and crop can be done without losing quality. Some restrictions (and the right software) apply.

[benwiggy]

Quote: Originally Posted by trevor Well, I don't want to argue semantics, but .... Resolution is the pixel dimensions of an image, like 1024 x 768 for example.

Semantics, you say?

Technically, resolution is dpi. It describes how close units of the image are, in order to be RESOLVED (i.e. observed as discrete units rather than a continuous image).

An image with the dimensions of 1024 x 768 pixels can of course be displayed in one of several resolutions: 300 dpi, 72 dpi, etc, which will obviously affect the actual size of the image as a whole. (Higher resolution == smaller image for the same number of dots.)

But you are right that the file size of a JPEG can be reduced by reducing the pixel dimensions of the image, AND by increasingly the compression level of the JPEGiness.

Saving a JPEG after editing the image will re-apply the JPEG compression to the [already] compressed data, which may cause further degradation, even for the same level of compression.

[trevor]

Quote: Originally Posted by benwiggy Semantics, you say? Technically, resolution is dpi. It describes how close units of the image are, in order to be RESOLVED (i.e. observed as discrete units rather than a continuous image). An image with the dimensions of 1024 x 768 pixels can of course be displayed in one of several resolutions: 300 dpi, 72 dpi, etc, which will obviously affect the actual size of the image as a whole. (Higher resolution == smaller image for the same number of dots.)

Ah, good point; you are correct. Image resolution is indeed shown in dots per inch. I was confusing it with display resolution, which has a fixed number of dots per inch depending on the display, and is shown as the pixel dimensions such as 1024 x 768, etc.

Image Resolution

Display Resolution

In any event, my point was that you can recompress JPEG images to make their file size smaller.

Trevor