Image compression

Post your tips & tricks here for creating slide shows with ProShow Gold. This could include suggestions for style and content in addition to working with the software itself
Esteemed Member
Posts: 297
Joined: Sun Oct 30, 2005 11:49 pm
Location: Bristol/Bath UK

Image compression

Postby Shaker » Mon Nov 19, 2007 1:44 am

This is well-covered in earlier threads. However, I wanted to investigate the pros and cons of compression for myself and hope the results may be of interest to others.

There is a price to be paid in terms of quality.

The following show demonstrates this. Uncompressed images are shown followed by their compressed versions. Compression is to an average of 13% of original size.

The differences at this and lesser compressions in PSG may be acceptable to some and is most noticeable with clouds and similar situations.

http://www.photodex.com/sharing/viewsho ... 8371&alb=0
Shaker

Captcurt

Postby Captcurt » Mon Nov 19, 2007 8:21 am

Of course this is simply an issue with the source image--it is not an issue for PSG. ie, it might help to move and load and handle smaller images but the way PSG renders the image for output is different than jpg.

I also beleive there are good compression tools and weaker ones. I mean the same % compression done from Photoshop isn't necessarily going to look the same as the same degree of comp from a different program.

PSG has no problems hanling large image files as far as I can tell. It does effect the rendering time, but all of the internal and on-screen rendering for previews are done to screen resolution or as set in the options window. I have used primarily tiff images and they are huge by comparison--it took an hour and a half to render the final product but the show looks excellent. I think that the final output means should be considered and then some margin of resolution better than that could be the highest required for pix. This especially makes sense if you are going to do zoom ins on the images. But using higher than screen res or display esolution just wastes storage space. (yes its cheap these days).

My general rule when prepping source images is this. If I can detect the difference from compression on a high res screen, then it is compressed way too much. I also zoom in according to the script to see how the image will look in the show. Thats how I ended up with lots of 200-600MB image files!

Nice effective demo! Thanks. Thats ALOT of compression. And where the first images jpg also? or something else?

FWIW

Curt

Esteemed Member
Posts: 297
Joined: Sun Oct 30, 2005 11:49 pm
Location: Bristol/Bath UK

Postby Shaker » Mon Nov 19, 2007 10:35 am

Curt,

I wasn't concerned at keeping the size down for PSG, but just allowing my camera to take more shots and cutting down on storage space. My camera produces only JPEG images.

Until I have finalised an image, I might have to store it as TIFF.

I had thought that if I saved as JPEG 100% between editing, I would retain the quality of the original. But trying this, I find that 100% compression gives a bigger file than the original. So things aren't exactly as I'd hoped and in a way which I don't understand. Because of this, I am not sure that 100% compression will retain all the original quality. Does anybody know if it does?
Shaker

Captcurt

Postby Captcurt » Mon Nov 19, 2007 11:18 am

What program are you using to edit and re-store?

It COULD be bigger than the original because it uses a different algorithm to compress the image.

It uncompresses the image for working then uses its own algorithm to save and compress it again--it could be bigger.

Curt

ProShow Hall of Fame
User avatar
Posts: 3143
Joined: Mon Nov 13, 2006 7:42 pm
Location: Northern Virginia

Postby DickK » Mon Nov 19, 2007 5:26 pm

Shaker wrote:...I had thought that if I saved as JPEG 100% between editing, I would retain the quality of the original. But trying this, I find that 100% compression gives a bigger file than the original. So things aren't exactly as I'd hoped and in a way which I don't understand. Because of this, I am not sure that 100% compression will retain all the original quality. Does anybody know if it does?

It will not and cannot. It's hard to explain because first I don't understand the details of JPEG compression all that well and second cause it's just plain complicated. I posted a thread with some info: http://www.proshowenthusiasts.com/viewt ... sion#38087

Never mind the math, the bottom line is that any time you save or resave an image as a JPG file type you will lose information. It may not be noticeable but it will happen. And the fact that the file size is grew just means that the original was compressed more than what you just saved. Saved at or near the 100% "quality factor" the image will lose less information and be compressed less, that's all. If you're going to do >1 edit and save cycles on an image always save it in whatever format the editor uses for intermediate saves or as a TIFF image. Only on the last save (if then) should you then put it back as a JPG to keep the file size down.

Now--there are a couple exceptions to the rule about editing a JPG. Many, but not all, viewers and editors implement a lossless rotation of the image and a few have the ability to do a lossless crop, tho' the options for the crop are limited. In these instances, doing these operations is safe and will not degrade the image. The software is actually manipulating the image file directly as a bunch of numbers (which is what a JPG is inside it) and never has to go through the expansion and then compression cycle that's otherwise needed. But with that as an exception, every time you load a JPG, it uses the numbers to calculate what the pixels will be and then when you save it there's a new calculation of those numbers and the process of that calculation introduces a loss of information (it's not quite right, but think of rounding errors).

Hope that helps,
Dick
"It is the mark of an educated mind to be able to entertain a thought without accepting it." Aristotle ((PSG, PSE & Fuji HS20 user)) Presentation Impact Blog

Esteemed Member
Posts: 297
Joined: Sun Oct 30, 2005 11:49 pm
Location: Bristol/Bath UK

Postby Shaker » Mon Nov 19, 2007 10:15 pm

Curt and Dick,

Thankyou for your reponses.

I edit using "PhotoImpact Bundled".

To check Curt's explanation that different algorithms could explain the growth at 100%, I saved at 100%, then opened the saved version and saved that at 100 %.

The sizes were:

Original 1.37 MB
Saved at 100% (A) 2.29 MB
Saved (A) at 100% 2.46 MB

So even when the same software's algorithm/s are used to decompress and compress, there is slight growth.
Shaker

Return to PSG - Tips & Tricks

Who is online

Users browsing this forum: No registered users and 2 guests