A problem saving a large image.

[wojt864]

Hi guys. I have a problem and can't find an answer.

I have some graphics (digital art) , which I would like to sell. Each of them has very large sizes so I reduced them to 50-70cm (Image size--"resampling" unchecked etc). I chose "Save as" and saved as a jpg file. Today I wanted to upload the file to one store but found that I can't. The allowed file size can be a maximum of 20mb. My file is 23mb. I found a few sites that allows me to compress the file to, even 2mb but my image then loses the color profile (sRGB) and I don't want that. After all, this profile is a requirement in printing houses. I have no idea how to get around this. Is there a way to save such a large file (50x70cm) to make it less than what it is now when saved (23mb)? In the store where I wanted to upload my graphics I saw images of the same size so it is certainly possible only, apparently I do not know how.

I will be very grateful for any help. Thx

[Mylenium]

Physical sizes mean nothing if you don't provide info on the DPI/ PPI and likewise file sizes mean nothing if you don't mention the file format and actual specs. You need to be much more specific. That said, a shop that only allows 20 MB for what is supposed to be high quality prints is probably just some outlet not worth putting up with. To put it mildly, that is sooooo 1990s and out of touch with today's reality where people send larger files with their smartphones. So perhaps consider finding another service?

Mylenium 

[wojt864]

Sorry. The PPI = 338

[D Fosse]

First of all, you need to get used to the idea that Photoshop only works with pixels. At the core it has no concept of size.

Size is determined later with the pixels per inch number (ppi), which is really just an instruction to the printer how much to spread out those pixels. It means exactly what it says: how many pixels to how many inches.

Given the pixels in your file, the ppi number determines the print size. The bigger the size, the lower the ppi number, and vice versa. In other words, ppi is a way to translate from pixels to a physical size. It's just a formula.

If your image prints 50 x 70 cm at 338 ppi, that means the file is 6654 x 9315 pixels. That's the true size of your image. At, say, 240 ppi (which, incidentally, would be more than enough here), it prints at 70 x 98 cm. And so on.

OK, so far so good. Now for the jpeg file format. Jpeg uses data compression to reduce file size on disk and transfer. Jpeg compression is destructive, non-reversible and cumulative, so don't resave a jpeg if you can avoid it. It will degrade with every save. The reason it's still used despite this rather serious drawback, is that the compression is incredibly effective. It can shrink a file down to 2 - 5% of native size!, with very little immediately visible quality loss. Standard procedure is to balance the compression level to small size vs. acceptable quality.

[Kevin Stohlmeyer · Accepted solution]

When you save as a jpg try changing the compression slider from 12 (Maximum) to 10.

Photoshop will estimate the image file size in that window for comparison.

Have you downloaded one of the other images to compare settings? Are you certain they are that large of a file size?

[Kevin Stohlmeyer]

Change the PPI to 300. 338 is an odd resolution.

[wojt864]

I can't belive how easy it was. Changing the value (slider) even from 12 to 11 when saving changed the image size from 23mb to 13mb. And the quality remained the same. Thanks a lot. However, can you tell me how to change the ppi without changing the image size? Is this even possible? I wanted to change the ppi to exactly 300 before, but that always changed the size of the image from 50x70cm to 56x82cm.

[Kevin Stohlmeyer]

Go to Image Menu/Image Size uncheck resample and change the resolution (the dimensions and resolution should be unlinked).

[wojt864]

This is exactly what I tried to do. When resampling is unchecked, the keylock next to the dimensions is inaccessible. I can't link or unlink it. Entering a ppi other than 338 always resizes the image.

[Kevin Stohlmeyer]

Try the opposite - check it. The link should be between w&h not resolution.

[wojt864]

Yes, it can be done and it works, but I don't know how resampling will affect the image quality. I have heard that this should not be done if you want to change the physical size of the image. It still looks very good on my monitor, but I will probably have to send my image to print to see it as a physical copy.

[Kevin Stohlmeyer]

Downrezing 338 to 300 wont affect the print.

[chrisg11235813]

will it let you save to JPEG2000? that has a better compression algorithm. But may have compatibility issues.

[Kevin Stohlmeyer]

JPEG2000 isn't accepted by a lot of stock sites as a valid format.

[chrisg11235813]

Yeah, that's what I figured.
Its too bad really, but it wouldn't be the first (or last) time a superior technology fails to gain popularity.