How do I reduce file size without affecting the printed quality in Affinity Designer or Affinity Photo?

[ScarletQueen]

Hi there:

I have a question about the file size for something that is going to be printed on merchandise that I am selling via print on demand. I am using Affinity Designer v2 on desktop, and I also have Affinity Photo.

I am creating car seat covers with the following dimensions and specifications: 2993 x 7703 pixels, CMYK and 150 dpi. The maximum size of the image file to be used by my supplier for printing is to be no more than 20 M (either in a JPG or PNG format with the sRGB color profile). 

I noticed that when I use a background that has a texture to it or that is more complicated, the file size for the image (JPG) gets larger than the 20 M that is allowable. Usually I fall into the allowable size with my designs, but now I have a car seat cover that I am working on that is exceeding 50 M. 

My question is: how do I reduce the file size of my image file without losing the printed quality of the design?

Looking forward to your response.

Thanks so much.

[NotMyFault]

Hi,

experiment with quality parameter of jpeg. Normally 85% does not have a visible difference to 100%.

try to reduce it until you get below target size, and inspect visible quality.

[ScarletQueen]

@NotMyFault Thank you!

Upsate: I had to go down to 80 percent to get the files size to be uploadable. My print partner said that the result was blurry in some parts. I guess the background is too busy, being a bit large and all. That said, I think I will have to make a new one that is less complex.

Thanks anyway. Trial and error I guess

[nickbatz]

Car seat covers, as in textile or even vinyl?

I can't imagine anyone would know the difference if you reduced the DPI to, say, 72 DPI (in addition to what NotMyFault says). But of course you'd have to experiment.

[ScarletQueen]

@nickbatz Thanks ... they are not vinyl, they are a polyester blend, printed via sublimation. I think they want 150 dpi. Perhaps 75 would be too low.

I think my best route is to redo the background to get a more simpler effect.

 

[Pšenda]

2 hours ago, ScarletQueen said:

dpi

DPI does not play a role in raster (non-vector) formats, and has no effect on file size - pixels are still just the same pixels.

[ScarletQueen]

@Pšenda Good to know. However, the file size increased with the multiple elements in the design. Usually when my background is complex, I get a larger file size when exporting to jpg or png, which means that I am unable to upload the design to my print on demand dashboard. As I lowered the quality in the settings during export, it seemed to have created blurriness in my overall design, according to my print partner. I guess that was my issue.. Most of my elements were vector. So I think that there was further pixelation that incurred blurriness.

[nickbatz]

3 hours ago, Pšenda said:

DPI does not play a role in raster (non-vector) formats, and has no effect on file size - pixels are still just the same pixels.

There are no vector graphics in this picture.

The JPEG on the left is 72 DPI, the one on the right is 300 DPI. 

[nickbatz]

And by the way, here's a tiny blob zoomed way in at 72 DPI and 300 DPI.

[ScarletQueen]

@nickbatz Not sure why you are referring to this ... you must be posting on the wrong thread. I never uploaded those and they are not mine. Please reread the main post.

Oh sorry, you tagged another person in this to demonstrate something. 

[nickbatz]

Right, those are mine. I'm posting in exactly the right thread. Please reread four posts up.

My point is that the DPI makes a huge difference to the file size (and to the resolution).

[ScarletQueen]

@nickbatz Right ... sorry about that. I reread your post after posting mine. Thanks for the demonstration. It is important for me to know this as a designer.

[Brian_J]

48 minutes ago, nickbatz said:

My point is that the DPI makes a huge difference to the file size (and to the resolution).

If a file is resampled when changing the DPI, the change in resolution effects file size and image quality. But DPI on its own has no effect… i.e., if DPI is changed without resembling.

[Pšenda]

4 hours ago, nickbatz said:

There are no vector graphics in this picture.

The JPEG on the left is 72 DPI, the one on the right is 300 DPI. 

Please indicate their resolution (ie how many pixels they have), the DPI size is not important. As OP write, the target resolution of his image is 2993 x 7703 pixels, and they will remain whatever the DPI is. For a JPEG file, the DPI value is just an entry in the metadata. 

[Pšenda]

4 hours ago, nickbatz said:

My point is that the DPI makes a huge difference to the file size (and to the resolution).

Yes, but that's not the OP's case - please read his first post, where it says that the resolution of the image is given and fixed (2993 x 7703 pixels), so there's no point in discussing the obvious fact that if I increase the resolution, I will of course increase the file size.

[NotMyFault]

you can’t have it all - large pixel count, fine details, good quality, small file size.

Especially a fine detailed texture will is very bad for compression.

never the less, 20 Mbyte is quite generous for the given pixel count. I create a test file where I added noise, with 100% quality it was 25MB, with 95% it was 15MB. The visual quality difference will be detectable when comparing 100% zoomed, but normally irrelevant when printed out.

In some cases PNG can compress better than JPG for fine details. Just check it out.

 

 

[NotMyFault]

You may try services like https://tinyjpg.com

which promise to create better results - and actually do according to some older discussion I can’t find right now.

 

[NotMyFault]

Another tipp: don't embed the color profile during export. This can add a few MB. 

[ScarletQueen]

@NotMyFault Thank you!

[ScarletQueen]

Thanks all! Your info was quite eye opening. 😊💕

[thomaso]

Another tool to reduce file size of JPG (+ PNG, + GIF) is https://imageoptim.com/   (with a downloadable app for macOS).

Although JPG is JPG the different apps can use different methods to compress and write their files. Thus an identical JPG compressed at 85% can result in different sizes depending on the writing application. – This website gives a quite good comparison of image detail / compression rate / file size for quite a bunch of different motives. (just scroll down to an image with enough details and hover over the compression rates):

http://regex.info/blog/lightroom-goodies/jpeg-quality

[R C-R]

3 hours ago, thomaso said:

Another tool to reduce file size of JPG (+ PNG, + GIF) is https://imageoptim.com/   (with a downloadable app for macOS).

I use this app for almost every JPEG I upload to the forum. To make it easy to do that, I keep an icon of it in the Dock so I can just drag & drop the JPEG onto it.

[nickbatz]

18 hours ago, Brian_J said:

If a file is resampled when changing the DPI, the change in resolution effects file size and image quality. But DPI on its own has no effect… i.e., if DPI is changed without resembling.

That's right, it's resampled, and you want to do that for the reason you can see in that example. But changing the DPI (with resampling) does affect the file size, as you say.

So it's pretty much a matter of semantics. Regardless of what's actually happening, you can lower the DPI and file size at a cost to the resolution that may or may not matter (probably not) if you're printing a car seat cover.

[Brian_J]

5 hours ago, nickbatz said:

But changing the DPI (with resampling) does affect the file size

I just wanted to make sure that forum members who aren't familiar with how DPI works in raster graphics — a confusing topic for many — understand that what Pšenda mentioned is correct...

On 6/16/2023 at 2:33 PM, Pšenda said:

DPI does not play a role in raster (non-vector) formats, and has no effect on file size - pixels are still just the same pixels.

[nickbatz]

By the way, can't the people doing the printing reduce the size? Surely they're in a better position to judge what the final thing is going to look like?

You also have to wonder why they have a 20MB restriction.