Creating large-scale high-resolution documents in Photoshop

Question

I am a student trying to create collages in Photoshop sized* 4' x 4' and larger, resolution 300dpi, to be digitally printed on cotton canvas and silk.

The enormous file size causes my iMac to lag or freeze. Many times the files will not save at all. I'm new working at these dimensions using Photoshop and came up with few solutions myself.

I have tried to work on the prints in smaller pieces and puzzle them together, but the results haven't been satisfactory. The only other option i have come up with is to lower the resolution, but that the printer has advised me that printing lower than 300dpi will adversely effect my final product.

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*) 4 ft = 121.92 cm

Answer 1

How close are you going to view the 4' canvas?

Is reducing the dpi really going to adversely affect printing on a coarse material like cotton or silk. Thats coarse relative to smooth glossy photo prints, for example.

See this recent question: What DPI should a large format artwork for print be done at?

Answer 2

Roger's right. You WILL NOT be in trouble at 150 ppi for an inkjet-type print process, especially at that size.

But let's pretend that you can't change the 300 ppi requirement. The problem you are running into is memory, and it may be an impossible hill to climb without upgrading your hardware, but here are some basic steps that can mitigate the problem:

• Make sure you have plenty of space on your hard drive (>100 GB would be good). Delete stuff if you have to. Just get plenty of swap space available.
• If possible, assign your first choice Photoshop scratch disk to something other than your system drive, and make sure it has plenty of space. It's under Preferences > Performance.
• In the same dialog, give Photoshop the maximum amount of memory possible (and, it goes without saying, don't have any other programs running).
• Set your Cache levels to 2 and reduce your History States to maybe 5 or 10.
• Set your Cache Tile size to 1024k.
• Before saving, use Edit > Purge > All to get as clean a slate as possible.

Beyond those points, there are a few best practices for when you're pushing the limits of your system's resources:

• Build your individual collage items separately, and use flattened versions in the "main" document, where you piece them all together.
• Don't use Smart Objects in your collage. Build outside of the main file.
• Use adjustment layers rather than pixel layers when possible (e.g. a Levels or Curves layer set to "Multiply" has exactly the same effect as copying a layer and changing its blend mode to multiply, but occupies far less space in memory or on disk)
• Use vector layers and vector masks when possible: they add minimal overhead to your file compared with pixel layers.
• Wherever possible, flatten layers. Every pixel layer adds overhead to your file size, and the bigger the document dimensions the bigger the overhead.

If none of the above works, you're gonna hafta add some RAM and/or get a bigger/extra hard drive. Remember the ancient America proverb: "You can never be too rich, too thin, or have too much RAM or disk space." :-)

Answer 3

This isn't really an answer, but I thought it might be easier to read in answer form than in comment form. One of the key things to remember about RGB images is that they are a grid of pixels, each square takes 1 byte (a value from 0 to 255), and there is one full grid for each color.

the grid size is the dots per inch (pixels per inch) multiplied by the final print size. Your 4x4 foot image:

48 x 300 = 14400px

14400 x 14400 = 207360000px (area of image)

207360000 x 3 colors = 622080000 bytes = 593MB

So your minimum file size is going to be half a gigabyte. Each layer adds something to this. If you duped a full color-flooded layer, you would see a doubling, but in my work, most layers are small fractions of the overall image size, and photoshop only needs to store the smaller bits.

What this means is basically what Alan said: ample RAM memory is crucial to working with these images at 300 dpi. You don't mention OS, but a 32-bit windows machine is pretty much maxed at 3GB of RAM. To put more RAM in your machine you'd need to know the OS can address it and your motherboard can accept it.

Of course, the more data there is to manipulate, the longer the CPU has to work to make that happen, so processor speed is a factor, but memory strikes me as a limiting factor in this case. Once the actual RAM is full, the OS has to start switching RAM data to the hard drive which is at least an order of magnitude slower than RAM. Which means go get some coffee while it works.

Answer 4

Nope - def stick with you 300 dpi if it's going to be in a gallery and upclose. But there are a few areas to consider tweaking...

1) Your machine's specs. You machine should ideally have dual quad core processors, 12+ GB of RAM, and a video card with a fair amount of onboard dedicated memory (like 512mb+). Also, using Mac over PC really helps on account of OS software architecture (take it from a 15 year windows convert).

2) Your document type and layers in Photoshop. If you're not using PSB files at that size instead of PSD, you need to make sure you save your document out as a PSB file. It's the Photoshop Large Document Format, specifically for Photoshop files over 200MB. Try simplifying your layers when possible. If you are running many layers, at 300dpi you'll start to really struggle. Merge layers when you can. Also, do you have your scratch disks set to a different hard drive than your operating system? There's tons more tips on Photoshop settings for performance from Adobe here.

3) How many other applications your machine is running. It should go without saying, but remember that when you're working on a document that large you should close as many other programs and tasks on your machine as possible.

4) If you do need to scale down proportions, look into a plugin like Genuine Fractals from OnOne software (made for enlarging).