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

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Posted By
windandwaves
Jun 14, 2007
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701
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5
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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
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MR
Mike Russell
Jun 14, 2007
"windandwaves" wrote in message
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….

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 – www.curvemeister.com
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Tacit
Jun 14, 2007
In article ,
windandwaves wrote:

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….

Save for Web automatically converts to RGB, because Web browsers can’t read CMYK JPEGs.

—
Photography, kink, polyamory, shareware, and more: all at http://www.xeromag.com/franklin.html
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Tacit
Jun 15, 2007
In article <H8kci.29606$>,
"Mike Russell" wrote:

CMYK images have less contrast and saturation than their RGB counterparts, so there is no problem with maintaining the quality when making this conversion.

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.

—
Photography, kink, polyamory, shareware, and more: all at http://www.xeromag.com/franklin.html
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nomail
Jun 15, 2007
tacit wrote:

In article <H8kci.29606$>,
"Mike Russell" wrote:

CMYK images have less contrast and saturation than their RGB counterparts, so there is no problem with maintaining the quality when making this conversion.

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.

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 johan<<at>>johanfoto.nl Editor / Photographer http://www.johanfoto.com
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windandwaves
Jun 18, 2007
thank you all for your answers, I will look into it!

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Easy-to-use drag-n-drop Photoshop scene creator with more than 2800 items.

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