File type and image quality/size

friviloususeofspace · Oct 30, 2013

In MS Windows I use a software called IrfanView for editing my photos. I don't do a lot of editing. Generally I crop and resize my photos because I take bird photos and I rarely get close enough to fill the frame. Sometimes I use another command in IrfanView that increases the light in the photo, since my camera seems to take underexposed photos. (Yes, I blame the camera.

)

After I've made my edits, when I save the new image, I have the option to use jpeg or other formats. I also can change what the program calls the "quality" of the photo with a slider. The program defaults to 80% and if I am saving in jpeg format, it means that the photos takes up about 3 megs of memory. If I push the slider to 100%, the same photo then takes up about a quarter of that size of memory for a jpeg. What is the tradeoff I am making here? It's telling me the "quality" is improved (100%), but the file size is smaller, so I don't understand what is going on.

I've never used Photoshop or $$ software like that, so I don't know what those apps do with regard to "quality". But in the open source world, the image editing suites I've used don't seem to have an analogous function. What would such a function possibly be called?

wyogirl · Oct 30, 2013

What is happening when you crop is that you are removing a large part of the file. You took say 25-50% of the photo and essentially deleted it so of course its smaller. Also, depending on how you are saving the file (jepg, tiff, gif, etc) you are most likely compressing the file even smaller.

friviloususeofspace · Oct 30, 2013

Amanda,
Thank you for the reply. Actually, the file size difference occurs after I've edited the photo and I go to save. If I save the cropped photo at 80% on the "quality" slider, then it's ~ 3mb. If I save at 100% "quality", then it's <600kb.

wyogirl · Oct 30, 2013

kb is a smaller unit of measurement than mb. That's kind of like 3 meters vs 6 feet.

friviloususeofspace · Oct 30, 2013

wyogirl said:
kb is a smaller unit of measurement than mb. That's kind of like 3 meters vs 6 feet.

Yes, it is. So when the image that is being saved at 100% quality (<600kb) is smaller in memory size than the 80% quality (3mb), I wonder what is happening.

KmH · Oct 30, 2013

That sounds backwards.
I would expect an image saved at 100% would have a larger file size than the same image saved at 80%.

Are you starting with a Raw file or some other file type?

GDHLEWIS · Oct 30, 2013

I used to use Corel Paintshop Pro and when you save at full quality on that it used to shrink the image size as a way of saving your comps memory. Took me ages to figure how to stop that but sounds like your program could be doing that as well. Are there any other option tabs in the save menu, if so try going through those you may find an image size tab.

The_Traveler · Oct 30, 2013

why not post links to the original and the two versions of saved files?

friviloususeofspace · Oct 31, 2013

Lew, et. al,
Here are links.

This is the photo as it was originally loaded into the computer: uncropped, saved at 80% quality and 2.33Mb

This is the photo cropped, but saved at 100% quality, 92kb

This is the photo, cropped and saved at 80%, 90kb (same memory as 100%).

This is the photo, uncropped and saved at 100%, ~318kb

So, in this case, my claim about the cropped photo saved at higher "quality" with less memory is not supported, however, the memory size is the same as the lower "quality" copy. The original size though does have smaller memory size for the higher quality copy than the 80% quality. Here is an example of the slider

Any guesses what this tradeoff is?

KmH · Oct 31, 2013

Nothing is out of whack with your software. Unfortunately, it seems you don't yet understand the technical details of cropping and the quality %.

The crop of #1 reduced the file size - a lot - basically from 2,333,000 bytes to 318,000 bytes

The files size of the croped #2 at 100%quality is a bigger file (318 kb), than the sam crop of #3 saved at 80% quality (90 kb).

For the same cropped version of the photo, reducing the quality % also lowered the file size.

friviloususeofspace · Nov 1, 2013

Unfortunately, I had the wrong links with the descriptions I wrote for each picture in my previous post. I tried to fix it all by editing the post, but it won't let me delete the linked images, so I can't move the images into the order I wanted. I fixed the mistakes in the post by editing the descriptions I wrote above each image, but the numbers are still:

------------------------ 80% quality --- 100% quality
Cropped photo - 92 kb --- 92kb
Uncropped photo - 2.33mb (~2330kb) --- 318kb
(I tried to make a table of the above lines, but I can't get the spacing to save properly. )

If an image file has a higher quality (don't know what that refers to), shouldn't it take up more memory, if everything else is the same?

robbins.photo · Nov 1, 2013

friviloususeofspace said:
Unfortunately, I had the wrong links with the descriptions I wrote for each picture in my previous post. I tried to fix it all by editing the post, but it won't let me delete the linked images, so I can't move the images into the order I wanted. I fixed the mistakes in the post by editing the descriptions I wrote above each image, but the numbers are still:

------------------------ 80% quality --- 100% quality
Cropped photo - 92 kb --- 92kb
Uncropped photo - 2.33mb (~2330kb) --- 318kb
(I tried to make a table of the above lines, but I can't get the spacing to save properly. )

If an image file has a higher quality (don't know what that refers to), shouldn't it take up more memory, if everything else is the same?

Ok, quick primer on JPG file format. A JPG is really just a form of file compression, what it does is reduce the image size by removing information about tone/color changes that it deems are too small for the human eye to differentiate. The reason your non-cropped image is coming out smaller than your cropped image (assuming that they were both compressed into jpeg from the same original source image) is that your non-cropped image has a lot more sky and a lot less bird - hence there is far more information about tonal/color changes involved that the JPG compression algorithm can remove, because the variations between one pixel of the sky and the next are not large enough for the compression algorithm to consider them worth keeping.

As to the "quality" setting, the higher the quality setting the more stringent the JPG file format is about removing information. The lower the quality, the more information JPG will remove when it compresses.