Why does photoshop reduce my file size after I make changes?

ulrichsd · Sep 21, 2011

Hello, I tried to google this one, but it only brings up pages about intentionally decreasing file size...

I am editing photos taken with my D90 on regular compression (I've since switched to fine and hope one day to switch to RAW) and the file size is about 3 MB. Both in Photoshop Elements (older version '03 I think?) and in Windows Photo Gallery, I'll make a few changes to brightness, contrast, etc., sometimes light cropping, but even with no cropping - I save it and the file size drops to around 1.5MB

Is anyone familiar with this? Is it compressing the image further? In PS, when I save I made sure the resolution was set to "maximum".

Thanks,
Scott

Tomasko · Sep 21, 2011

It isn't only about resolution, but there's a thing called "jpeg compression". It seems you have it set the way it compresses your image during save, so make sure that feature is off. (probably impossible with windows gallery, but you can surely find that in Elements)
I just don't understand why you don't use raw? You have semi-pro D90 and you're just wasting its potential this way. What's so difficult about it for you? If you don't want to play with sliders, you can use just the settings you've already set in camera and just hit one button...Convert.

Robin Usagani · Sep 21, 2011

If you have a JPEG image and you press save as another jpeg multiple times, the quality will degrade even if you didnt make any changes and you set it to save at maximum quality each time.

KenC · Sep 21, 2011

As proposed above, shoot RAW, and then when you convert, work with uncompressed TIFF or PSD files only, and convert to JPG only for web or to send to an outside printer.

clanthar · Sep 21, 2011

JPEG is an aggressive compression format that achieves it's goal by discarding content. Every time you edit and re-save a JPEG as a JPEG the algorithm goes to work to do what it was created to do -- throw away more of your photo. It's job is to throw away as much of your photo as it can. Give it a second chance and it will try again and succeed.

I use a digital camera to take photos that I eventually print. As such JPEG NEVER occurs in my workflow.

If you do have to create in camera JPEG originals you should stop the JPEG damage there. Any edits that you do should be done to copies of those originals and the edited files should NEVER be re-saved as JPEGs. Those edits should be saved as TIFF or PSD or some other non-destructive format. If you need a JPEG you can create one from the non-compressed edit.

Joe

GooniesNeverSayDie11 · Sep 21, 2011

Why not shoot RAW now? Other than taking up more card space, and slowing down frame rates and bursts on certain cameras, there really is nothing daunting about shooting RAW. You can have ACR or Lightroom presets set to your liking so that if you did need a quick on the fly JPEG with some settings tweaked ( like in-camera processing would do ) You click 1 button and save the file. Then if you actually want to do more indepth stuff, you can skip over the auto function and manually tweak settings or open in CS5 ( or a similar program )

KmH · Sep 21, 2011

Photoshop is not reducing the file size.

JPEG is a lossy, compressed, 8-bit depth file type, intended as a print ready file that would not have any additional editing done to it.

JPEG applies it's lossy, compression algorithm every time a JPEG image is saved, or saved as (not just opened and closed), even if no edits were done.

With JPEG set as your capture file type, when you trip the shutter on your camera the image sensor makes a Raw image data file (12 or 14-bit depth) that the camera software immediately applies the JPEG lossy, compression algorithm to. If you capture the Raw image data file the Raw file gets written directly to the memory card for conversion to an image outside the camera.

The first thing the JPEG algorithm does is discard about 80% of the color data the image sensor captured, the first big step in compressing the file size. (All of the luminance data is retained.)
Next, the JPEG algorithm converts the pixels in the image into concurrent 8x8, 8x16, or 16x16 pixels areas known as Minimum Coded Units (MCUs), to accompish even more file compression to reduce the bit depth to 8-bits.

With little, if any, input from you global, standard, pre-canned edits to contrast, saturation, and sharpening are then made based on what the camera software engineers decided would be appropriate. Of course they made those decisions long before you ever released the shutter so the edits are one-size-fits-all(few).

JPEGs have little, if any, editing headroom because they are 8-bit depth files that only retain about 20% of the original color information, and that have had the pixels converted to MCUs.

Check out this group of tutorials: Photo Editing Tutorials

ulrichsd · Sep 21, 2011

So, I guess it is unanimous. :sexywink:

I rarely do more editing to my photos than slight tilt, crop, exposure or resizing. But I guess it sounds like I should just start shooting RAW.

The reason I was asking is because I was thinking of submitting some pictures to a photo contest but they require a minimum of 3mb files and my files are currently 3mb and after editing are way below the limit. I'll try to find a way to turn off the compression in PS.

KmH · Sep 21, 2011

The only way you can 'turn off the compression' is to convert your unedited JPEGs to TIFF or .PSD, neither being lossy compressed file types like JPEG is.

However, you still then likely need to save them as JPEGs for upload to the contest which will reduce the file size again.

Tomasko · Sep 21, 2011

KmH, you're wrong. I don't have Photoshop, but with Gimp it IS possible to save it without loosing any data, over and over. When you're saving a file, a dialog popups asking you the settings, one of which is Quality. If you slide that to the right (100), you'll find out, that the new file is sometimes even bigger than older jpeg. Just tried it especially for you with one of example images that came with Windows 7. 826kB (old) vs 0,99MB (new = the same, but saved under a different name).
It's true, that jpeg is lossy file, BUT, you can decide how much. There is no fixed value... You can preserve the quality of the file when saving, so please, don't confuse other people...
Don't confuse this with converting raw files to jpeg, because that is a different story

Jpeg will never get the same data as raw, but I hope that's clear already to everyone...

KmH · Sep 21, 2011

JPEG is lossy every time it is saved.

The Quality setting isn't eliminating data loss, but yes the file size can be controlled to an extent by using the Quality slider.

Tomasko · Sep 21, 2011

KmH, I know the theory, but have you actually tried it? Are you just repeating the well-known stuff or have you done some research on your own? Because I did and compared the two images side by side, pixel by pixel in random spots (literally, I zoomed in as close as possible so I could see actual pixels). No change whatsoever with setting Quality at 100 in Gimp. Please, explain

I honestly want to know.

clanthar · Sep 21, 2011

Tomasko said:
KmH, I know the theory, but have you actually tried it? Are you just repeating the well-known stuff or have you done some research on your own? Because I did and compared the two images side by side, pixel by pixel in random spots (literally, I zoomed in as close as possible so I could see actual pixels). No change whatsoever with setting Quality at 100 in Gimp. Please, explain I honestly want to know.

Did you make an edit change to the photo between saves? I believe the issue is reapplying the JPEG algorithm to a JPEG file between edits. If you have the JPEG quality set to the highest value you may not end up with a smaller file then after an edit. That doesn't mean the algorithm won't have done other damage as it re-scans the image. I just ran a quick and by no means thorough test. I took a TIFF file and reduced it to 1280 pixels wide. I saved it as a JPEG in Photoshop (max quality) and it came out as 916kb. I edited it and re-saved it 4 times and it went down to 842kb and on the 5th edit and re-save it went back up to 860kb.

I'm not going to keep it up, but I'd say this isn't a positive process for this photo.

Joe

Tomasko · Sep 21, 2011

clanthar said:
Tomasko said:

KmH, I know the theory, but have you actually tried it? Are you just repeating the well-known stuff or have you done some research on your own? Because I did and compared the two images side by side, pixel by pixel in random spots (literally, I zoomed in as close as possible so I could see actual pixels). No change whatsoever with setting Quality at 100 in Gimp. Please, explain I honestly want to know.

Click to expand...

Did you make an edit change to the photo between saves? I believe the issue is reapplying the JPEG algorithm to a JPEG file between edits. If you have the JPEG quality set to the highest value you may not end up with a smaller file then after an edit. That doesn't mean the algorithm won't have done other damage as it re-scans the image. I just ran a quick and by no means thorough test. I took a TIFF file and reduced it to 1280 pixels wide. I saved it as a JPEG in Photoshop (max quality) and it came out as 916kb. I edited it and re-saved it 4 times and it went down to 842kb and on the 5th edit and re-save it went back up to 860kb.

I'm not going to keep it up, but I'd say this isn't a positive process for this photo.

Joe

I didn't edit the image. I took an image and saved it as a new file (dialog Save as...). Then I closed Gimp, reopened the new file and saved it as the same file (through the dialog Save as..., not Save...). In theory, that should have compressed the image twice = the file should have been smaller, but it was the opposite - it was actually bigger than the original. Pixels themselves remained the same and the image looks exactly the same even at biggest zoom.
I'll try the same approach with some editing and post the results later if anyone is interested...