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

[Tomasko]

It's true, that jpeg is lossy file.

Which contradicts the point that you are trying to make. Unless, of course, you do not understand what LOSSY means.

Don't play smart ass against a guy who works in IT and try to explain what actually happens with the image using the settings I've posted...

 

[GooniesNeverSayDie11]

OHHHHHH, I forgot, IT guys are one step shy of being Steven Hawking. Pretty pompous to brag on your IT status like you are some kind of genius. Nothing smart ass about it, it was you who started spouting off and accusing people of being wrong. I just merely pointed out your contradiction. You agree that JPEG is lossy, yet argue that it doesn't lose quality when compressed ( saved ). Now, I am not "IT GUY" but that sounds sort of like a contradiction.

 

[Tomasko]

In other words, you don't have anything to say but to argue about one word? Good one, now you can happily return under your bridge You didn't say anything new and you obviously DON'T understand what actually happens, nor you're willing to try it yourself and at least attempt to explain, WHY it doesn't act the way anyone would expect.

 

[GooniesNeverSayDie11]

My guess is that the compression method was changed. See Below. Perhaps instead of pretending to be a genius, you should hit the books, before they outsource your job to India :thumbup:



The progressive mode allows the DC components to be sent first, followed by the DCT coefficients in a low- frequency to high-frequency order. This enables the decoder to reproduce a low quality version of the image quickly, before successive (higher frequency) coefficients and received and decoded. The image data can be organised into two or more 'strips' of DCT information, resulting in two or more possible preview images.

Figure 8. Two step progressive JPEG decoding.
The principle advantage of this mode is the ability to quickly view a low quality version of the image. The Disadvantages are:

• The file size of images JPEG encoded this way are slightly increased.
• The decoder requires a buffer for all the partial (and final) DCT coefficients.
• The decoder has to recompute and display the final image every time it receives a new strip of DCT information.

 

[GooniesNeverSayDie11]

In the words of Kelso........"BURRRRRNN!"


I should add, that I am not seriously trying to insult your or anything, although the "IT" comment did come off a little snobbish. Just busting your stones a little. ( not sure if that term translates well to Slovakia )

 

[Overread]

*in the words of moderator* Keep it civil darn it!

 

[KmH]

It's true, that jpeg is lossy file.

Which contradicts the point that you are trying to make. Unless, of course, you do not understand what LOSSY means.

Don't play smart ass against a guy who works in IT and try to explain what actually happens with the image using the settings I've posted...

The thread was about Photoshop. GIMP, isn't Photoshop.

GIMP was/is not germain to the discussion.

I did some more checking into how Photoshop (not GIMP) applies the Quality setting.

Even at the highest setting, 12, there is some file compression. Certainly there is considerably more compression at the lowest setting of 0.

However, I was unaware that unlike most other applications the JPEG compressor Photoshop uses is convergent, such that repeatedly opening and saving the same JPEG without modifying the pixels, the data loss diminishes with each save such that eventually there is little or no data loss.

 

[GooniesNeverSayDie11]

No worries, Guvna. Keeping it Civil with a capital "C". (what happened to the cheese grin emoticon? )

 

[clanthar]

Which contradicts the point that you are trying to make. Unless, of course, you do not understand what LOSSY means.

Don't play smart ass against a guy who works in IT and try to explain what actually happens with the image using the settings I've posted...

The thread was about Photoshop. GIMP, isn't Photoshop.

GIMP was/is not germain to the discussion.

I did some more checking into how Photoshop (not GIMP) applies the Quality setting.

Even at the highest setting, 12, there is some file compression. Certainly there is considerably more compression at the lowest setting of 0.

However, I was unaware that unlike most other applications the JPEG comprssor Photoshop uses is convergent such that repeatedly opening and saving the same JPEG without modifying the pixels, the data loss diminishes with each save such that eventually there is little or no data loss.

I believe the whole key here is as Keith is saying "modifying the pixels." There's no reason to run a Save As operation on an unaltered file. And once you've done something like make a Levels adjustment or color balance adjustment the JPEG algorithm is going to go back after that file in a save operation. I think it's a fair bet then that JPEG is going to do more harm regardless of the quality setting. That has been my experience. I've never know JPEG to improve a photo.

Joe

 

[manaheim]

So, I guess it is unanimous. 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.

Careful. RAW is a pandora's box. Very valuable, and I never shoot in anything else really... but it's a LOT to take on. Perhaps an interim step might be shooting or at least saving your files as TIFF. (shooting in TIFF would be better than just saving in them)

TIFF is a non-lossy compression algorythm.

 

[marmots]

but have you actually tried it

ok i just tried it

i made a macro for my computer, and did exactly what you did, only 500 times more

it took a 15mb file to an under 1mb file

 

[shmne]

Facts are facts.

Jpegs are lossy. Period. There is no argument about this.
If you have any understanding of how file compression works then you would not be trying to argue this fact. Let me explain since there is a clear misunderstanding going on.

If you slide the quality slider to 100% guess what is happening? There is an algorithm being applied that does NOTHING. That is why you are finding out that your file size is larger with no difference. There is a second layer of compression embedded into the file that ends up beefing up the size without changing the file.

This is the difference between professional software and freeware. Photoshop would never allow this because it is completely useless, potentially harms the image, and in the end will increase file size. Also do note that "max" on photoshop jpeg compression appears to be 10, but actually is 12.

Saving a jpg, as jpg is very hazardous to your file's health and may cause banding as well as artifacting.

Again this is not opinion, this is fact. If you have questions about compression please consult google about compression, there are very lengthy articles I am sure. My knowledge comes from my teacher in college who helped develop algorithms for compression. I trust his explanation of how things work quite a bit

 

[manaheim]

I can't believe anyone is seriously debating this point.

I swear some people just like to shout at the rain.

 

[clanthar]

If you slide the quality slider to 100% guess what is happening? There is an algorithm being applied that does NOTHING. That is why you are finding out that your file size is larger with no difference.

This is incredible! The algorithm does nothing and yet the file size is larger and yet there is no difference. I'm going to meditate on that. Maybe if I got stoned?

There is a second layer of compression embedded into the file that ends up beefing up the size without changing the file.

Sneaky! Change the file without changing the file, of course! Why couldn't I see it! JPEG was created by Congressional economists!!

Also do note that "max" on photoshop jpeg compression appears to be 10, but actually is 12.

I know! That has always bothered me. When I pull the JPEG slider in Photoshop to the far right end it says 12 but it appears like a 10! How do they do that?!!!

Joe

 

[shmne]

If you slide the quality slider to 100% guess what is happening? There is an algorithm being applied that does NOTHING. That is why you are finding out that your file size is larger with no difference.

This is incredible! The algorithm does nothing and yet the file size is larger and yet there is no difference. I'm going to meditate on that. Maybe if I got stoned?

There is a second layer of compression embedded into the file that ends up beefing up the size without changing the file.

Sneaky! Change the file without changing the file, of course! Why couldn't I see it! JPEG was created by Congressional economists!!

Also do note that "max" on photoshop jpeg compression appears to be 10, but actually is 12.

I know! That has always bothered me. When I pull the JPEG slider in Photoshop to the far right end it says 12 but it appears like a 10! How do they do that?!!!

Joe

Actually you're right it isn't Photoshop that does that, it is Adobe Camera Raw :

It says 10 is the max, but really 12 is. Sorry I don't save in lossy formats normally so I couldn't remember which application it was.

Alright I don't know if you're trolling or if you just completely missed what I sought to simplify and explain in an easy to absorb manner. What I explained is completely correct, there is much more detail than what I stated but what I stated is true. My lecture notes take about 30 minutes to go through, and it is not something I look forward to typing out to an audience that will not understand a vast majority of it.

Jpg is math. Math takes work. Work adds file size.

[ JPEG ] - this jpg compression takes up 1mb to be applied to an image, but it drops a 10mb file down to 200kb.
[ JPEG ] - This is the same compression. It still takes up 1mb. The computer must still run it. This also drops a 10mb file down to 200kb, however since there is an already existing jpeg compression it just takes what the previous one does and repeats it.

The file is now 2mb and 200kb instead of just being 1mb and 200 kb.

Another way to visual this:

{Jpeg [ File ] }
{Jpeg {Jpeg [ File ] }}

Which is bigger ? If you answered the bottom one, you're right! Congrats.

So to recap, 1+1 = 2.
2 > 1.
Therefore, the more you add, the more you have! I'm so glad we had this discussion. Thanks :3