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I have a 8640x12120px poster template in PSD. It is in CMYK and has a size of 120 MB.

After pasting a 8640x4790px 4MB JPEG photo, the size of PSD file increases to 350 MB. Is there a way to avoid this and keep the size closer to the sum of originals?

Update: I tested it from scratch by pasting another 4000x3000px 4.5 MB JPG photo to a new empty 8000x12000px 7 MB PSD (CMYK/8). The PSD's size instantly increased to 104 MB. Using "Place" option instead of pasting produces 108 MB PSD.

  • Have you tried placing it instead of copy/pasting it? – curious Aug 27 '17 at 2:29
  • Can you describe the composition of your PSD better (verbally or visually)? At the moment there's too many unknowns to advise. For example, I don't know if the posted image creates a new layer over the layer(s) that existed in the original 120mb file or both outputs are flattened PSDs? – biscuitstack Aug 28 '17 at 11:53
  • @Emilie I tried to place (embedded or linked) and it's only 10 MB smaller. – Ivan Mir Aug 28 '17 at 15:27
  • @biscuitstack I just cleaned the whole PSD for the test. Empty it's 7 MB, adding a single photo gets it to 302 MB. – Ivan Mir Aug 28 '17 at 15:56
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    FYI: uncompressed image size for CMYK (4 channels) is width x height x 4 bytes. 8640x4790px is about 150MB. Also, file types are for storage not for display: no image you can see on screen is compressed, and there is no such thing as a JPEG photo (they are Photos stored in JFIF using Jpeg compression). It is unclear what you mean by "instantly increased." If you mean the info showed in the status bar, then "yeah, sounds about right" since Photoshop is showing you actual data size. – Yorik Aug 29 '17 at 16:58
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I'll preface this by saying that you still haven't provided enough information about the before and after files for me to be certain of any answer. Ideally, showing the composition of layers and their properties would help a lot.

You also haven't expressed your understanding of jpeg compression so I don't know if my answer is repeating information you already know. Nonetheless, I hope it's useful:


Edit: I'm just after seeing your answer to a separate question on png files, it appears that you're likely familiar with everything I describe below, which means I may have guessed the missing details of your question wrong. I'll leave it incase it's useful for anybody else as it's still relevant to the current details should anyone be searching for the same question.
I have a hunch that this is down to confusion over how various files (PSDs and JPEGs) store their information.

JPEG

Jpegs shrink the filesize of images by lossy compression, meaning that if you have an image that's 10 pixels by 10 pixels, it can save it in a filesize smaller than it would have typically taken to store what those 100 pixels were, but that the 100 pixels would't be identical to the originals. Hence, lossy. It's advantage is that we can't, typically, perceieve that they're different with our eyes. The more compression you use, the more likely we are to perceive it.

PSD

PhotoShop PSDs also use compression to shrink filesize but, conversely, it's lossless - meaning that whatever tricks it uses to shrink the filesize of 10 pixels by 10 pixels, the resulting 100 pixels will be identical to the original 100 pixels.

This has an advantage in image data integrity. You will likely be editing the images and want to know each save and open of the file is exactly as you left it.

The disadvantage is that this type of compression doesn't produce as drastic a reduction in file sizes as JPEG.

Saving JPEGs as PSDs

If you have a PSD open in PhotoShop at 10 pixels by 10 pixels, you can bring a JPEG into the software by any means (placing, copying and pasting, etc.) but once it's saved, the 100 pixels of JPEG information are saved using the PSD compression technique instead. They are now just 100 pixels, not a JPEGs impression of 100 pixels. The filesize will likely go up.

But how does the filesize stay down on massive layers of pure colour or large areas of colour?

This is one area that PSD compression is good at. Shrinking the filesize dramatically on areas of the same colour. So blank layers and white layers of any dimensions will have a very small file size. Introduce a photograph or drawing as another layer (or in place of that layer) and the PSD can no longer see lots of the same colour next to each other and can't hope to keep the file size nearly as small when it tries to compress.

Pixel Previews

It's worth knowing that for speed of editing and previewing, PhotoShop also saves a hidden preview layer of each layer in your PSD at 1:1 pixels. This little known piece of information answers a lot of confusion about ballooning filesizes and frustrations as to how smart objects and copies of smart objects can see file sizes increase against the belief of how they're expected to work. I digress, but it's related to the subject and useful to know.

If the information here was all already known to you or is way off the problem, I'd suggest editing the question to include a lot more information about the before and after files.

  • Thanks for the detailed answer! Yes, I understand image formats and didn't go into details in the question because I assumed there's just some "magic" option in Photoshop that I'm missing. I was expecting to keep JPEG kind of "embed" inside a PSD. Placing imported smart objects looks close enough but PS still keep them lossless. – Ivan Mir Aug 29 '17 at 23:20
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    I can see how this could make sense. Look at it from PhotoShop's primary purpose as an editor. Having an embedded jpeg would only make sense as long as the embedded jpeg wasn't altered from its original form. Since PhotoShop is an editor, this will be a niche situation and not worth adding the extra convolution and maintenance. File size just isn't nearly as high a priority as data integrity and speed of editing/viewing. – biscuitstack Aug 30 '17 at 8:38
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    I should clarify that the data integrety mentioned in my comment above and in my answer is from the perspective of a pixel of x value colour being guaranteed to still be a pixel of x value colour on multiple saves and reopens. jpeg saving methods do not guarantee this. This is as opposed to the perspective of data integrety I was not suggesting, where if a block of image information was saved as a a compressed 4mb image, could that block of information not remain a compressed 4mb image inside the PSD? – biscuitstack Aug 30 '17 at 9:13

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