Difference in file size between Save and Save As for JPG?

[jungleexplorer]

So I am working with some jpg images shot on a DSLR. The images are around 5.5Mb out of the camera. After I edit them and I go to save them I can choose from Save and Save As. If I just choose SAVE, the file will over write the original, but the file size drops from 5.5Mb down to 4.5 Mb. Now if I choose the SAVE AS option and select Best Quality, the file size will jump way up. I have had some files jump to 27Mb. Why is this happening?

[hartpaul]

"around 5.5Mb out of the camera" does not tell much
Are these jpgs from the camera?
what pixel dimensions are they?

In PSP X8, X9 and 2018 when you hit Save you were redirected to Save As for the first save in a session to enable you to set your compression.
In earlier versions back to X4 at least Save used a default compression of 20.


" I have had some files jump to 27Mb. " To get that I had to resize a complex jpg photo to 11000 x 7500.

[LeviFiction]

JPG uses a special table of wave forms to simulate the data in an image. It also determines what it can throw away and what it needs to keep. No two programs do this in exactly the same way. So there is the first discrepancy. PSP saves with different set of parameters resulting in a different file size. For most people even though the file is smaller they usually can't tell the difference between the original and the new so no quality has been lost even though the file size is smaller. In my opinion it's always best to save a copy and never overwrite the original. But that's me.

Actually when Corel changed the JPG engine they used and people started noticing big changes in their file sizes at generally the same compression everyone complained. They were afraid PSP was decreasing the quality of their images.

As for the difference between Save and SaveAs. SaveAs lets you choose the compression of your image. Save does not. So when you choose the best quality during Save As you're using less compression than the general Save option is. Because you're using less compression the file retains more pixel data and is therefore larger.

[jungleexplorer]

JPG uses a special table of wave forms to simulate the data in an image. It also determines what it can throw away and what it needs to keep. No two programs do this in exactly the same way. So there is the first discrepancy. PSP saves with different set of parameters resulting in a different file size. For most people even though the file is smaller they usually can't tell the difference between the original and the new so no quality has been lost even though the file size is smaller. In my opinion it's always best to save a copy and never overwrite the original. But that's me.

Actually when Corel changed the JPG engine they used and people started noticing big changes in their file sizes at generally the same compression everyone complained. They were afraid PSP was decreasing the quality of their images.

As for the difference between Save and SaveAs. SaveAs lets you choose the compression of your image. Save does not. So when you choose the best quality during Save As you're using less compression than the general Save option is. Because you're using less compression the file retains more pixel data and is therefore larger.

I understand what a JPEG (Joint Photographic Expert Group) is and how it works, but this does not explain where 20+Mb of additional data is coming from. Logic would dictate that if s JPG files is 5.5MB and you save it at Zero compression, the resulting file should be no larger then 5.5Mb. Now since JPEG is a Lossy format, each time you save it, even if in the same program, it is recompressed and recompressed, and loses information each time. But in PSP I am now seeing that it is somehow gaining massive amounts of information, when I use the Save As function, VS the Save function. The question is, WHY and where is all this additional data coming from, especially, when I am not resizing the image.

[LeviFiction]

I assumed the 5.5Mb was on disk. Which means in file, compressed by the camera. And since, as you know, JPG doesn't save pixel perfect representations the size on disk is going to be smaller than the size in memory or non-compressed and pixel by pixel in size. Which means that if you save at zero compression it will convert the in memory data to the disk resulting in larger than 5.5Mb. I'm not saying an extra 20 is reasonable, but that expecting no more than 5.5Mb only makes sense if that's the size in memory or if the original JPG was not compressed at all. The fact that saving by default resulted in only a 4.5Mb image would suggest it was closely compessed to PSP's default compression rate already.

[jungleexplorer]

I assumed the 5.5Mb was on disk. Which means in file, compressed by the camera. And since, as you know, JPG doesn't save pixel perfect representations the size on disk is going to be smaller than the size in memory or non-compressed and pixel by pixel in size. Which means that if you save at zero compression it will convert the in memory data to the disk resulting in larger than 5.5Mb. I'm not saying an extra 20 is reasonable, but that expecting no more than 5.5Mb only makes sense if that's the size in memory or if the original JPG was not compressed at all. The fact that saving by default resulted in only a 4.5Mb image would suggest it was closely compessed to PSP's default compression rate already.

I did expect a little bump in size do to the fact that I enhanced the photos with a littler extra color and stuff, but never in my 20 years of editing JPGs on many image editing programs have I ever seen a jump like this. Sure, you might pick up a couple extra megabytes do to enhancements, but 20+..... Something does not seem right. I have never got these kind of results with any other program I have ever used. I just started using PSP for enhancement, so I am feeling it out.

Take this image for example.


The disk size of this JPG file out of the camera is 5.57Mb. The size of this file after enhancement, (Vibrancy, Sharpen, Contrast) using the Save Function is 7.43Mb. The size of this same file (after enhancement using the Save As function is 28.9Mb (Lossless Encoding and do not save EXIF Info, do not Embed ICC Profile).

[LeviFiction]

Well as hartpaul asked, what are your pixel dimensions? Not to be a pain but you gave us a resized image, while it does give us an idea of the variation in color and complexity of the image that's about all it does.

I don't have a DSLR but my Google Pixel does well enough for me. 4048x3036. One image I have is 7MB on disk, when saved with lossless compression it gets up to 18Mb. GIMP at 100 percent quality saves at 14MB. But doesn't have a lossless option. Do you have an example of a program that provides a lossless JPEG conversion instead of just maximum quality setting for comparison?

[hartpaul]

Ok with the image available I did a few tests.
Here are the results:

01. I right clicked the image in Firefox and did a save image which gave (01) Original photo at 163KB
02. I also did a right click and copy and pasted as a new image in PSPX9 version 19.1.0.29
When (01) was dropped into the workspace and using PSP Info , the image showed 162K on disk and 1582K in RAM.
(This is close to the size of the .bmp image (08))
I then did a Save which for the first time in a session defaulted to the Save As dialog where I set the compression to 1 and completed the save - (02) 671 KB. I then renamed so that I could do a direct Save with out overwriting 02.
03. The Save produced (03) also 671 bytes so in this case Save is using the same compression as set by Save As.
04. I then applied an unsharp mask with radius 2 strength 100 and clipping 5. I did a Save As and this gave (04) which at 977KB . This is an increase of 600% on the original .
05. Did a direct Save and the size is very similar to that of the Save As.
06. I used the soften brush to soften the lower third bushes on left and right and did a Save As and renamed - 571 KB
07. Undid the steps and did an Unsharp as in 04 and then softened the bushes as in 06 . This gave a middle value of 760 KB between the soften only (06) and the sharpen only (04,05)
08 Saved the image obtained in 07 as a .bmp file- close to the image size in RAM
09. Savd as .png
10 Saved as .pspimage
11. Saved as .tif which gave the largest disk size image . Note that all these images gave the same size in RAM.
12. When I did these previous saves I had used the image that I copied and pasted which seemed larger than the 01 Original image saved from the browser so I did a Save via Save As similar to 02 and there was a less than 1% variation
13. Again a direct Save produced the same size as a Save As at 688 Kb.
The size of the saved image will depend on the complexity of the image. Large amounts of same or very similar colors or soft areas will reduce the size. Greater amounts of complex details and sharpened images will produce larger images.
As for losses of information by repeated saving of a jpg, I once saw an image with a sunset sky gradient which had been saved 29 times and clearly showed the degradation in the sky. I thought at the time , why did they not show the image after just 5 saves or was it not visible at that stage.
I have found with tests that there is very little visible change from the first 5 saves doing minimal compression, so that is relatively safe. But how many people do jpg saves over and over again. When working on the same image over a number of sessions you are best to save it as a .pspimage and only do your final save(s) as jpgs.

[jungleexplorer]

The image I posted is not the original. The forum system would not let me post an original photo, it has a maximum resolution limit of 900 pixels wide. I uploaded that image to my facebook and then used a URL link to embed it into the post, so it also went through facebook compression. I appreciate all the testing you did, but it did not know you were going to do that. If I had known that is what you were going to do I would have provided you and original image. As such I am not sure much can be told from the testing you did.

I tried attaching an original file to this post, but I cannot. The max file size is 2 MB.

[LeviFiction]

The original would be nice if possible, Google drive, or Dropbox ate options if you have them. But also just the original pixel size would be of help even if you can't get the original file to us.

[hartpaul]

Actually I beg to differ there. The changes in the size of your image using different methods are valid irrespective of the size of the image down to a point. In general a jpg at minimum compression will be smaller in disc size than a bmp, tif, .png and pspfile. If you follow the steps I described using your larger image you should obtain parallel results.

Should the image get too small however say 10 x 10 pixels then the amount of overheads can actually make the jpg larger than the bmp.

eg a landscape photo 5616 x 3744 pixels saves as

bmp - 61 601 KB
jpg at compression 01 - 12 812 KB

Resizing that to 900 x 600 pixels gives :

bmp - 1583 KB
jpg - 693 KB

so using your image at the smaller posted size still keeps the relative sizes. So the table I presented and methods used to obtain the images is still valid.


As an aside however when you do get to a smaller size eg 10 x 10 pixels, 100 x 100 pixels then the overheads involved in compresssion of a complex image can make the jpg larger than the bmp.
eg a 10 x 10 pixel multicolor image (this posted image is of course scaled larger)

bmp - 374 bytes - ie 100 pixels each pixel represented by 3 bytes for the red, green, blue channels + an extra 74 bytes for the overheads.
jpg - 7970 bytes because of the extra overheads for each pixel

So in general most processing of an original jpg image can result in a size increase if the complexity of the image is increased - eg sharpen increasing contrast.
Softening of parts of an original image can result in a size decrease.

In your image the large image from the camera will already have had some compression applied to it but minimal sharpening unless you set it to extra sharpening and contrast in camera.

Your subject material in this case consists of lots of finely detailed leaves on the bushes and branches and twigs. (You compared the size out of the camera with the size of saved images after processing and wondered why you obtained much more information. )
At the larger size these will be more easily compressed as there may be 100 pixels representing the shading of a twig or leaf with colors close together. In the reduced size image posted there may only be 10 or 20 pixels representing the same twig or leaf and so less pixels with a similar color allowing less compression.

[MarkZ]

To start, let me say that I don't understand what goes on when files are saved at different compressions. but I've been involved in a number of discussions on the subject and keep finding out new things, as when I did some more experimenting now.

I started with a jpg of about 9.2 MB and saved that at various compressions between 1 (0 not available) and 90 using SaveAs. Here is the data for the experiment:

File sizes at different compression

I found that:
- dimensions for all the saved files were the same as the original, 4896 x 3264.
- the quality of the images did not seem to change, did not suffer as the compression increased.
- for this image the default compression for Save appears to be about 15

Now since JPEG is a Lossy format, each time you save it, even if in the same program, it is recompressed and recompressed, and loses information each time. But in PSP I am now seeing that it is somehow gaining massive amounts of information, when I use the Save As function, VS the Save function. The question is, WHY and where is all this additional data coming from, especially, when I am not resizing the image.

Yes. I remember experimenting with repeated saves and finding the pixelation increasing and quality dropping off when saving an image a number of times. But I think that with the algorithms that PSP uses that is no longer the case. I did not try this but I think if you save a jpg repeatedly using the same compression, for example using just Save with its default compression, the file size will not change to any degree.

In PSP X8, X9 and 2018 when you hit Save you were redirected to Save As for the first save in a session to enable you to set your compression.
In earlier versions back to X4 at least Save used a default compression of 20.

This statement implies that when you have set the compression at that first save that that compression will be used for the rest of the session. That is the compression that will be used for that file for that session. But if, in the same session, you start working on a different file the first Save will be a silent one - no prompt - and the compression will be the default, not what you used with the first image you saved.

I re-opened the image for which I used a compression of 90 and used SaveAs with a compression of 1. The size of the resulting image was identical to the image that I save with a compression of 1 starting with the original!! Where is all the data stored and where does it come from?

Here is a portion of the image I worked with, the original and the one at compression 90.

Original jpg and compression 90

[jungleexplorer]

Thanks MarkZ. Great stuff there, but you ended up in the same place as why I started this thread. With no answers to the question, where does all the massive amount of EXTRA data come from?

"I re-opened the image for which I used a compression of 90 and used SaveAs with a compression of 1. The size of the resulting image was identical to the image that I save with a compression of 1 starting with the original!! Where is all the data stored and where does it come from?"