Does post processing affect file size?

Sony 16-50mm f/3.5-5.6 E-mount

03/07/2003 11:59:11 AM · #1

I have a picture that I really like for bridges and after I post processed the image, it was 650Kb at 640x480. I went to go save for web and I got a quality output of 52 for that file size. Is there something I'm missing here or does post processing add a lot to the photo size?

jmsetzler

Sony Alpha a6000

03/07/2003 12:00:57 PM · #2

I find that images with lots of detail and lots of different colors make much larger files. Sharpening also increases file size...

03/07/2003 12:09:19 PM · #3

well slap me with a wet noodle, that eliminates one photo

Gren

Fujifilm FinePix 3800

03/07/2003 02:27:41 PM · #4

Also black and white images tend to have smaller file sizes than full (high) color images.

timj351

Sony DSC-F707

03/07/2003 04:05:21 PM · #5

Achiral, are you sure you are reading the Save for Web file information correctly? You really should have no problem compressing a 640x480 image down to 150k with good quality.

T

Tamron SP AF 28-75mm f/2.8 XR Di for Canon

03/07/2003 04:18:05 PM · #6

i think i'm doing it right, it has worked for me before. i can only get a quality of 52 when optimizing for 150kb

W.R.Miller

Canon EOS-50D

03/07/2003 04:21:15 PM · #7

If you are using PhotoShop (not sure if you are), when you save as .jpg file type it will allow you adjust the quality and as long as you have the preview option checked it will allow you to view the output file size prior to saving. This is how I save my files at the 640x480 / 150kb size while maintaining a quality, no jpg artifact photo.

Hope this might help some. :-|

03/07/2003 04:36:52 PM · #8

i don't know what you are refering to when you say preview button. the original file size is 1000kb. at 640x480 it is at 560kb

Gordon

RIM BlackBerry Curve

Canon EF 85mm f/1.8 USM

03/07/2003 04:58:56 PM · #9

It does depend on the file - I've had images with lots of detail that I can't compress to under 150k , at 640x640, without using a quality of 50 or less in 'save for web'

The problem there is there is a step change in the compression used that made my file go from 151k at 51 compression value, and 112k at 50 compression value - and the quality was terrible.

With enough detail, compression can't do a good job at getting under 150k at these sizes, nor should it be expected to.

I use 'save for web' and the optimise to file size options, where you get to type in the target file size and it tries the various ratios until it gets a match under the given size. Sometimes it just can't do a good job - too much information in the picture.

Message edited by author 2003-03-07 17:00:06.

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

03/07/2003 05:03:48 PM · #10

Originally posted by achiral:

i don't know what you are refering to when you say preview button. the original file size is 1000kb. at 640x480 it is at 560kb

Try using Save For Web rather than Save As (PS 7). That should give you an interactive panel enabling you to save at the largest allowed size.

Uncompressed file size is entirely dependent on pixel size and color depth: H x W x nColors x 8(bits/color)
Compressed file size adds color variation and detail to the equation, each requiring higher compression (lower quality) in order to reach a specific file size (in bytes).

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

03/07/2003 05:08:12 PM · #11

Originally posted by Gordon:

Workarounds I use when the file size is close to 150k is to crop just a few more pixels, or add/thicken a solid color border at the expense of a few pixels of image. I once got a file from 151k to 148k by adding a 3 point solid stroke to the photo.
I did the same with another photo by going back to the edited TIFF and applying less sharpening than I first tried; the extra sharpening added something like 4-8k to the file size.

Message edited by author 2003-03-07 17:13:15.

Gordon

RIM BlackBerry Curve

Canon EF 85mm f/1.8 USM

03/07/2003 05:10:30 PM · #12

Originally posted by GeneralE:

Yup these will work, but even there, after doing that kind of thing I was only able to get it to the right size with a jpeg compression value of 51, which still screws the quality up pretty badly. I gave up and found a less detailed subject. The original shot was a macro of a car light - lots of repeating squares with a large amount of small, sharp detail and rapidly changing colours.

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

03/07/2003 05:15:41 PM · #13

Originally posted by Gordon:

The original shot was a macro of a car light - lots of repeating squares with a large amount of small, sharp detail and rapidly changing colours.

Sounds like a great shot for demonstrating the limitations of image compression schemes. Probably looked pretty good, too!

Sony DT 11-18mm f/4.5-5.6 Aspherical ED Super Wide Angle Zoom

03/07/2003 05:18:16 PM · #14

i like that border idea, good thinking

JPR

Sony Alpha a55

03/07/2003 05:56:21 PM · #15

The whole image compression thing is a mystery to me as well. I mean, I know how it works, but it still seems pretty random and hard to deal with for posting to this site. Is there any way we could convince the kind folks here to raise the maximum file size to at least 200. I often get stuck in the same situation you were all talking about where it will jump from 151 to 110. It really sucks and I don't like to have to take time figuring that crap out. I wonder if it has to do with the quality of the original image. It might be a coincidence, but I usually shoot it HQ mode on my camera because the file size is smaller. I started taking them as Tiffs so that I could print them out at larger sizes and I found that when I make them 640x480 that they are much bigger then my old ones were and they don't seem to look any better. Wierd stuff. Makes me want to beat my computer with my digital camera.

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

03/07/2003 09:21:12 PM · #16

Originally posted by JasonPR:

...I usually shoot it HQ mode on my camera because the file size is smaller. I started taking them as Tiffs so that I could print them out at larger sizes and I found that when I make them 640x480 that they are much bigger then my old ones were and they don't seem to look any better. Wierd stuff. Makes me want to beat my computer with my digital camera.

If your Oly uses the same settings as mine, the HQ setting is medium-quality JPEG, SHQ is highest-quality JPEG, and the TIFFS are uncompressed. One problem is that you need to edit and save changes in an uncompressed format -- NOT JPEG -- or you accumulate compression degradation each time you save it. I always convert the file I'm editing into Photoshop format, and save a TIFF intermediary of the final version.

In addition, TIFF files can be saved with LZW compression, which will make the file smaller on disk, but will not discard any data, so the image can be re-opened with full fidelity. However, it may take longer to open or print, since the file must be decompressed first.

Be thankful you don't have to look at the file itself -- 150kb is about 75 pages of typewritten code...

03/07/2003 09:43:54 PM · #17

so is it best to take pictures in tiff format, do the editing, then convert to jpeg?

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

03/07/2003 09:51:00 PM · #18

As long as you have the memory for your camera, yes TIFF is the best quality you can take (check if your camera supports RAW format -- I think that's also lossless quality but smaller than TIFF). Since they are bigger files than the JPEGs, you may also have a longer delay before you can take the next shot, and be limited in burst mode. You'll have to check your manual for those specs. Other than these factors, there is no reason to not shoot in TIFF or RAW, especially if you want to enlarge (resample up) the image to make large prints or to crop tightly.