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A
Anonymous
November 9, 2010
Question

Rasterize/Flatten Image

  • November 9, 2010
  • 1 reply
  • 32705 views

Hey guys, I have a couple of questions wanted to know if you could help me out. I know these are probably geared more toward photoshop but I was just curious. Under the Layer menu there is a function called 'Rasterize', what does this do and what is it for?

Second one, let's say I wanted to send a file to the printer from photoshop. Would I want to flatten the image (also under the Layer menu at the bottom) to send a smaller file size or send the file as separate layers? What is the better of the two?

Lastly, if you have a vector image in illustrator or photoshop is it preferrable to keep it vector rather than raster for any reason(s)?

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    1 reply

    E
    Eugene Tyson
    Braniac
    November 9, 2010

    Firstly this is the InDesign forum - you could navigate back to the main forum pages and select the Photoshop forums for photoshop queries.

    Rasterize in the Layers Panel will convert any vector object in Photoshop, vector shapes, vector masks or text to Pixels. Meaning they will lose their scalability as increasing raster physical dimensions causes interpolation (jaggy edges)

    Sending a file from Photoshop to the printers is precarious depending on file format

    TIFF and PSD can both retain layers, including vector layers, type layers, vector shapes and vector masks - BUT they both output the data as Raster

    EPS can retain the vector information only for PRINTING - if you open an EPS in photoshop again it is completely flattened and rasterised - http://livedocs.adobe.com/en_US/Photoshop/10.0/help.html?content=WSfd1234e1c4b69f30ea53e41001031ab64-78f7.html

    EPS also does not retain layers, and it can be problematic http://www.prepressure.com/library/file-formats/eps

    The IDEAL format then is to use the PDF option when saving a file from Photoshop. The PDF can retain layers, vector information for editing later and also outputs the vector and raster data - it's fully retains the objects as it wraps them in a PDF wrapper ensuring they output correctly.

    Lastly-

    It is preferable to keep it vector and sometimes it is prefereable to rasterise it.

    Vectors are sometimes best left as VECTORs as they can be increased or decreased to any size without losing sharpness.

    But some Vector objects from Illustrator are very complex and yield massive file sizes. If you had a 10 x 100 mb vector images in a document, that would be a 1gb of information for just those vectors. It may be best to rasterise these vectors at 300 ppi at actual print size, which could reduce the file size significantly - you may or may not notice quality issues with it - depends on the content of the image, something with sharp edges, like buildings may be more noticeable, but an illustration of a painting with soft edges may not be so noticeable.

    Hope that helps.


      A
      Anonymous
      November 9, 2010

      Okay, only reason I asked on here is because anytime I've asked advice on the photoshop wing of the forum I seldom got a response and when I did it wasn't very helpful but ok.

      So basically the answer to my first question sort of goes hand in hand with the third question I asked, if the file is too big as vector then I should rasterize it? It was meant to shrink file size?

      To what you're saying about the PDF wrapper, does it really make any difference whether the original file has separate layers or one flattened single layer when in print?

      dumb question: if I open a vector (.ai file) in photoshop as a vector file and then save it as TIFF or PSD it now becomes raster?

      E
      Eugene Tyson
      Braniac
      November 9, 2010

      jiyasa wrote:

      So basically the answer to my first question sort of goes hand in hand with the third question I asked, if the file is too big as vector then I should rasterize it? It was meant to shrink file size?

      You do not have to rasterise the file if the file size is too big. I know printing companies that RIP 10gb of information for print jobs. BUT if you needed to get the file size down for whatever reason - then you can rasterise the vector, but you will lose some quality and sharpness - it may or may not be noticeable in print. But this rasterised version should only be used to get the file size down - you should always keep the vector as the master file.

      jiyasa wrote:

      To what you're saying about the PDF wrapper, does it really make any difference whether the original file has separate layers or one flattened single layer when in print?

      If you make an EPS - be sure to save another version as an editable PDF/TIFF/PSD file in photoshop - that way you can edit the text or other vectors again. If you save a file as an eps and open that again, everything is rasterised and flattened to a single layer. So why bother saving as an eps in the first place (Placing to Quark is one example of why you'd need an EPS file - as it will retain the vectors for outputting). But you should always always always have an editable version of the file to make changes.

      If you have  TIFF or PSD with text layers, you can open that in Photoshop and adjust the text. Then when you print it the text is rasterised, it's not vector, so it loses it's sharpeness.

      If you make a PDF from photoshop - it will retain the text layers for altering at a different date, plus it retains the Sharpness of the vector in print.

      So just save it as aPDF to start with - and you won't clutter up your system with different versions of the file.

      jiyasa wrote:

      dumb question: if I open a vector (.ai file) in photoshop as a vector file and then save it as TIFF or PSD it now becomes raster?

      Yes - when you open or place an Illustrator file in Photoshop it becomes a Smart Object. Smart Objects are denoted in the Layers Panel. A smart object is a vector object that can be scaled in Photoshop without losing resolution. BUT it is converted to RASTER on output at the native resolution of the document.

      SO:

      If you start a new document and choose 300 ppi (or any res)

      Then place an AI file it becomes a smart object

      You can now scale that within Photoshop to ANY size you want and it retains it's vector sharpness

      BUT when you output (even to PDF) the image gets' rasterised to 300 ppi (or whatever resolution you choose)

      THE only thing that PDF can out put as vector from Photoshop are Text Layers, Vector Masks and Vector shapes created within Photoshop.

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