reducing images and keeping quality going from large CMYK jpg to small web jpg

Discussion in 'Photoshop Tutorials' started by windandwaves, Jun 14, 2007.

  1. windandwaves

    windandwaves Guest

    Hi Folk

    If I would like to reduce images while keeping quality as good as it
    can be - going from large CMYK jpg images (e.g. 20 Megabyte) to small
    jpg images for the web (10kb) then what steps should I take? Should i
    just reduce and save for the web (high quality) or do I also need to
    convert to RGB, choose specific reduction methods, etc....

    Thanks in advance

    Nicolaas
     
    windandwaves, Jun 14, 2007
    #1
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  2. windandwaves

    Mike Russell Guest

    CMYK images have less contrast and saturation than their RGB counterparts,
    so there is no problem with maintaining the quality when making this
    conversion. In general you will get a better looking image by converting to
    either sRGB or Lab and bumping color and contrast to cover the full nominal
    range of black to white. Particular images may benefit from special
    treatment - for example it's easy to boost green foliage in Lab. Then, if
    necessary, convert to sRGB, and save for web.

    If time is limited, for example if you have 100's of these to do in a short
    time, run auto-color on each image before saving, or auto-levels and
    auto-color and pick the best of the two.

    Sharpening is another important part of conversion, particularly for
    relatively small images. Generally Photoshop's Unsharp Mask has enough
    flexibility to get very good quality. If you are using Lab, sharpening is
    best done in that color space, on the Lightness channel only.

    Compression works. If you are limited by file size, and not the pixel
    dimensions, then for a given file size you will get a better result with a
    lower jpeg quality setting, and a larger image.
     
    Mike Russell, Jun 15, 2007
    #2
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  3. windandwaves

    tacit Guest

    Save for Web automatically converts to RGB, because Web browsers can't
    read CMYK JPEGs.
     
    tacit, Jun 15, 2007
    #3
  4. windandwaves

    tacit Guest

    Untrue--or at least, misleading.

    CMYK does not offer as much saturation in some colors, notably blues. In
    some other colors, such as yellow, CMYK allows *more* saturation than
    RGB.

    CMYK's range of contrast is greater than RGB's, in part because you're
    working with a black channel, which allows for a great deal of contrast
    and shadow detail.
     
    tacit, Jun 15, 2007
    #4
  5. Actually, it's even more complicated than that. You and Mike are talking
    about 'RGB' and 'CMYK' as if they are color *spaces*, but they are not.
    RGB and CMYK are color *models*, and you have to specify a specific
    color *space* within that model before you can make any meaningful
    comparison. Some RGB color spaces, such as ProPhotoRGB, allow more
    saturated yellow than almost any CMYK color space. Of course, if you
    compare different CMYK spaces with sRGB specifically (because the images
    are destined for the web), the remark about yellow is quite true.
     
    Johan W. Elzenga, Jun 15, 2007
    #5
  6. windandwaves

    windandwaves Guest

    thank you all for your answers, I will look into it!
     
    windandwaves, Jun 18, 2007
    #6
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