Which Quality for JPEG did you choose + online compression

[amirw2k]

Hi all,

I'm trying to balance between file-size and quality of the image and I found out that when using the default 80% quality for JPEG, a picture can go from a live picture to a blury one.

I am planning a public gallery that people will be able to upload pictures to, and I'm using GD2 with coppermine 1.42. I want the pictures to be 800x600 and with maximum file-size of 200kb.

There are two issues that I'm concerned about:
1. I don't want to limit the upload file-size to 200kb (only the stored file-size)
2. I found out that when you upload an image under the maximum allowed image dimensions, no conversion is taking place (e.g I upload an image with dimension 800x600 and file-size of 500kb).

If I upload a 800x600 image with the size of 500kb, it will not resize and take a lot of space on the server. I can use watermarking to avoid this issue, but this requires watermarking and I'm not sure that I want to do that.

To sum it up, what are your best recomendations to keep a picture alive after an online conversion without keeping the file-size huge? Is there any advantage of ImageMagick over GD2 regarding image compression? Do you think that limiting a 800x600 image to 200kb can affect the quality? What's the best size for 800x600 images in your opinon?

Thanks for your replies,
Amir W.

[ecto]

Do you think that limiting a 800x600 image to 200kb can affect the quality? What's the best size for 800x600 images in your opinon?

No, absolutely not. I use Photoshop to batch-resize my images from 2560x1920 to 800x600 before posting them in my gallery, and my images are ~100 kB. Most of them are actually _below_ 100 kB, and I don't see image quality as a problem. I can't see any compression artifacts when viewing my images in 1280x1020. ~100 kB images are fine for web viewing - I mean, an 800x600 image isn't going to be printed anyway.

I don't know about the quality of GD's or IM's conversion, but if they are even remotely close to Photoshop's abilities a 200 kB 800x600 image will be prefectly fine - even overkill imo.

[Joachim Müller]

I agree with ecto: this is not a matter of compression, but a question what algorhythm is being used to resize the images. Both GD and ImageMagick can't compete with good desktop apps when it comes to resizing, so I suggest you resize on your client (using Photoshop or similar). AFter all, GD and IM are server apps that are meant to do a quick-and-dirty job, without using too much memory, cpu load etc.

[amirw2k]

Thanks for your replies, you've helped a lot 

This is what I was afraid of, losing quality because of GD2. I've converted my entire gallery using GD2 + watermark and there's a loss of quality in the pictures but it's not that bad. I guess I'll have to compromise since the only option is to do it myself and when it comes to autmoatic on the server vs. time wasted, then I guess I'll settle on the automatic option.

[kegobeer]

I wrote a script in Photoshop that automatically resizes all loaded images to 640x480, and saves all of the new images to another directory, then discards the original image without changes.  Very efficient.  I'd much rather resize my images before uploading them.  I guess it all depends on what you call "time wasted".

[amirw2k]

What I mean is that I want to let the users control their images. What they did up until now is mail me a big zip file with all the images, but I want the gallery  to work similar to public galleries such as flickr.com or others.

As for resize, I used ACDSee which is pretty fast with batch resizing.

[ecto]

amirw2k, you should put a note on your site asking your users to resize before uploading. If you look around a bit, I'm sure you'll find lots of info on how to batch-resize images with freeware programs like IrfanView or XnView, and you can put a link to such a guide on your site. Maybe it'd save you some time and image quality