Photoshop Jpeg


Everytime I open say a 2 megabyte Jpg image in photoshop, do a little clone stamping, and save the file again, the jpeg size is now 10 MB, why does the file size change so much? How does it get so big?

Thank you
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Kyle SantosQuality AssuranceCommented:
It's because PSDs are not a compressed format like JPEGs and PNGs are.  
Here are some tips and tricks you might benefit from to keep file sizes reduced.

Let me know if you need anything else!


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FCapoAuthor Commented:
I know PSDs are bigger in size, I'm taking about saving the file in JPEG format from photoshop, the original file size is 2 MB, re-saving it in the same JPEG format from photoshop (after making minor changes to the image) makes the size go up to 10 MB
Kyle SantosQuality AssuranceCommented:
JPEG is a lossy format and it has variable quality levels which result in larger or smaller file sizes. Whenever you save a file in a lossy format, additional detail is lost, so even though you saved the finished version as a higher quality JPEG, it is still actually lower quality than the original was, despite the growth in the file size. It is still closer to the original image than it would have been if you had used a lower compression quality and re-compressed the image.

Put really basically, JPEG is trying to fit an image to a pattern. The lower the quality of the compression, the more looser the fit is allowed to be, which reduces the file size, but also means more detail is lost. Conversely, a high quality requires that the compressed file much more exactly match whatever you had originally opened, but means that the file also must be much larger.

One other way to think about it is that the actual data held in a JPEG, uncompressed, is much larger than the size of the JPEG. You can open a very highly compressed image or a very slightly compressed image, but both actually have the same number of pixels with the same bit depth, which takes far more space than compressed file size. When you choose a higher quality, you get less compression of that large amount of data than if you use a low quality/high compression setting.
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Dan CraciunIT ConsultantCommented:
Instead of doing a save, do a Save for Web (CTRL+ALT+SHIFT+S). That way you will have full control over the compression.

FCapoAuthor Commented:
I understand what you're saying regarding compression and photoshop,

The issue I'm having is that opening a 2MB JPEG file in photoshop and resaving it adds 5 megabytes to the jpg size, this without even touching or doing anything to it in photoshop. I figured that I must be using the wrong compression or something...

My question was why can't I save it back in to the original format without adding 5 megabytes to it? I haven't done or edited anything in the picture
Dan CraciunIT ConsultantCommented:
Probably because using Save (CTRL+S) uses maximum quality, while your original JPEG was compressed at 40-60%.

PS: Never resave a JPEG. The already compressed picture will be compressed again, so the result will always be worse. Use TIFF or PNG until it's time to use it again on the web.
FCapoAuthor Commented:
Ahh ok, the original file is a jpeg and I have no choice but to re-save it in jpg because that's the needed format,

I was just wondering if there a way to edit a jpg in photoshop and save it back in to jpg without re-compressing the image, I guess I was using too much of my imagination :)
David BruggeCommented:
Hi F,

Let me weigh in here because I have wrestled with this very same problem in the past.

Think of it this way. The jpeg compression algorithm starts from scratch each time it saves. In that sense, it has no idea if the file was compressed before or not, or if it is a high quality or a low quality image.

I had the mistaken idea that if I had a 2 meg jpg with a high compression and I saved it again at highest quality, it should be very close to the original compression without adding much more degredation. Thus, my expectations that it would be close to the original 2 meg. As you have discovered, this is wrong.

The reason is just as Kyle stated, the uncompressed image has the same pixel count and bit depth as the original, just with a crappier quality.

The compression algorithm doesn't care about the quality, it's just going to see a file size of so many pixels at such and so bit depth, and start compressing. Whatever quality was in the image the first time it was decompressed, will be degraded a bit more this time around. How much more, depends on your new compression settings. The point being, the size of the new saved version has no direct relationship to the size of the first saved version, it's always starting over from scratch.

You might want to take Dan's advice and use the "Save for Web and Devices" where you can see a full screen preview of the effects of your new compression setting as well as monitor the size of the final file.
Ali EslamifarUXCommented:

This is a typical issue in photoshop, but don't worry, there are always a lot of tricks in photoshop. So open you JPG file, then use the selector and copy (Ctrl+C) the entire image. Then hit Ctrl+N to create a new file, since you saved that image, photoshop automatically puts the ratio for that image as the ratio for the file that you want to create. You can also change the resolution underneath of the height for the new file. It is recommended to put 72 if it is gonna be used in the web. Now hit OK button, then use Ctrl+V to paste the image that you've already copied, then Ctrl+S to save the file, be careful to select the JPEG format once you wanted to save the file, now press SAVE button, you will see a prompt that shows you the quality of the image, I normally use a quality around 8- 10 for images that I want to use in web. Underneath of preview check box you can track the file size that you are gonna have at the end. So select the file size that you prefer and press OK.

I had the same issue several times, and this technique always works. I hope it helps for you as well.
David BruggeCommented:
Hi Ali,

Just a couple of notes regarding your advice.

If what you are trying to do by pasting the copied image into a new work area, is to trigger the jpeg save quality dialogue box, you can achieve the same result in a little bit easier way by simply selecting "save as" from the file menu. This of course is also achieved using the "save for web and devices" which not only opens the save quality dialogue, but other features as well. For the record, "save for web and devices" strips out the meta data that is normally saved in the background. The savings is not much, usually 10-15k, but it is something that you can not do using the regular save or save as.

Regarding the resolution. The resolution setting has absolutely no effect on web images except in a few instances when the image is output onto a printer. All modern browsers look at an images pixel width and height and go from there. If there is not any code to enlarge it or reduce it on the screen, it will display at that resolution completely ignoring the 72dpi resolution anyway. Besides that, folks haven't been setting their monitor to 72dpi since the dark ages.

Thanks for giving me an opportunity to clear these points up.
Ali EslamifarUXCommented:
Hi David!

I offered this solution because I know that there are sometime in jpg files that the "save as" action is not working to resolve this issue, this was absolutely based on my experience and the solution works.

Have a nice day.
Selena JainGraphics DesignerCommented:
Very simple, just use the Save for Web option and it will be in reduced size.
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