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I have a set of images of up to 20mb each, and I want to reduce the file size without losing quality.

How can I do it?

share|improve this question
By "size" do you simply mean file size? Resolution? pixel dimensions? What are you going to use the images for in the end? – Lauren Ipsum Oct 29 '12 at 12:06
actually i like to maintain photo quality which is actually after reducing photo file size. – Ashish4434 Oct 29 '12 at 12:11
What's the file format? – Yisela Oct 29 '12 at 19:25
up vote 2 down vote accepted

Reducing the size is possible if your 20mb images are in an uncompressed format (RAW, BMP etc.). If you need to maintain the quality, you will need to use a so-called lossless compressor such as TIFF with LZW, PNG etc. JPEG will remove information and therefor also quality.

If you mean reducing the pixel size of an image it will always remove information, hence also remove quality. So this is not possible. You can apply techniques such as sharpening convolution to make it appear as if it is the same quality, but technically it will not be.

In either case you can create a batch script in Photoshop to do this for you. There are plenty of resources and tutorials on the net for this, so I won't write a new one. But have a look at for example this one:

Additionally, if you need this for storage purposes (I didn't get that impression, but this can serve as a tip), look into the open-source (and free) 7-zip compressor. This can compress any file type, but will also compress none-JPEG image files a little more as well as allowing you to use encryption on the resulting archive. Ideal for transporting in the cloud.

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your ref link and idea is nice one,thanks. – Ashish4434 Oct 30 '12 at 5:35
@Ashish4434 If Abdias' answer has helped you, you can choose it as the best one by clicking in the tick under the voting buttons. – Yisela Oct 30 '12 at 19:50

Simply put, you can't.

Imagine you have a dumpster full of tennis balls. You want to take all those tennis balls and put them into a 50 gallon barrel. They simply won't all fit. This holds true for pixels in images. In order for the image to fit into a smaller container, you're going to have to discard some pixels (information).

Now you may be able to reduce the container size with an acceptable amount of loss. For example, if you have a 20MB image in .tiff format. You may be able to save that image as a jpg set to 12 quality and find the resulting jpg, while much smaller, appears very much the same as the tiff.

In general, saving an image as a jpg with the highest quality setting will dramatically reduce the files size. While using the jpg format will in fact throw away image data, at the highest quality setting that data is often an aceptable loss.

Just be aware you can only do this once. Never, ever, save a jpg image as a jpg again. You immediately start drastically degrading any image when you do so.

In reality there's not a whole lof of information provided in your question - current format, image uses, types of images, are you editing the images, source of the images..... The actual question mentions 'resolution' but your post only refers to 'size'.

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If the images are in JPEG or PNG format, then you can use lossless image optimizers such as optipng, pngout and jpegtran.

Those tools re-compress images and spend extra CPU time to apply heavier compression. With 20MB files this could take several minutes per file though.

Try the SuperPNG plugin for Photoshop.

On Mac there's ImageOptim that combines all those tools. For Linux there's Trimage and for Windows punypng web service.

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In short, you can't. What you can do though is:

  • trim the images that don't fit in the canvas
  • delete hidden elements/images
  • use the proper file colorspace (don't use CMYK if it's something meant to be used for the web. Use RGB instead).
  • merging layers should also help if you are willing to loose the ability to change one of the merged layers afterwards.

If you have images in a loss-less format (like TIFF), you could try compressing the PSD file (ZIP is ok, but BZ2 should do a better job).

share|improve this answer works great by reducing unseen color data.

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Hello JBizzle, welcome to GDSE! Thanks for your answer. Could you elaborate a bit more on your answer? What type of software is it (online or desktop)? Is it free? How does it work exactly? What benefit does it hold over similar tools? – PieBie Sep 3 '15 at 13:48

use helps me better always

best, gauri

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We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

Gauri, could you explain why you think/know that InDesign does a better job than Photoshop, and how? Otherwise this doesn't seem like a very helpful answer. – Johannes Nov 17 '15 at 16:16

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