How Do You Compress Photos?

[Son of Spam]

Many times I want to upload photos of myself to websites as profile photos or for other professional reasons.  I have some examples but they're too large.  Most of these sites ask for photos no larger than

120x100 or 240x260.  When I resize my photos smaller, they appear very blurry and pixely. 

 

What's a way around that so I can meet the compression requirements of these sites without compromising the integrity of the photo?

[pdnnoob]

If the site wants a photo to be less than a certain size in pixels, you really can't get around that. There's no way to trick the site into thinking you have an image smaller than it really is.

[Visual]

This is one of my hopes for the coding guys to do. In photoshop you can resize as a smart object a lose no quality.

Maybe they can make a plugin for pdn?

[Ego Eram Reputo]

... you can resize as a smart object a lose no quality.

 

This CANNOT be done without losing quality, somewhere, unless you're working with vector images - which Paint.NET does not.  A raster application like Paint.NET must either blend pixels together or entirely remove them in order to make an image take up fewer pixels.  Pixel removal by seam carving gets close.

 

 

To answer the original question:  You need to resize the image by a factor of two.  Halve the size or quarter it.  1/8 or 1/16 will also work.  Reductions of this order blend an equivalent number of source pixels to reach a smaller number of output pixels, so the blending is uniform across the image.  If necessary, crop your image beforehand so that a factor-of-two reduction brings it down to the target size.

 

You can always run Effects > Photo > Sharpen (at a size of 1 or 2) to enhance detail following a size reduction.

[Visual]

To answer the original question:  You need to resize the image by a factor of two.  Halve the size or quarter it.  1/8 or 1/16 will also work.  Reductions of this order blend an equivalent number of source pixels to reach a smaller number of output pixels, so the blending is uniform across the image.  If necessary, crop your image beforehand so that a factor-of-two reduction brings it down to the target size.

 

You can always run Effects > Photo > Sharpen (at a size of 1 or 2) to enhance detail following a size reduction.

 

Didn't realize that it was only vectors when reducing as a smart object. Thanks for schooling me EER. It seems to be another math equation and why this is the case?

[Ego Eram Reputo]

Consider a 16x16 pixels image.

If we halve the size we end up with an 8x8 image. To achieve this compression, blocks of 2x2 pixels are blended together to give each resultant pixel. In over simple terms, each of the four source pixels might comprise 25% of the final output pixel.

Now consider resizing the original to 9x9 instead of 8x8. The source image doesn't fit evenly into the new size as 16/9 is not a whole number like 16/8=2. This means that some of the output pixels will be blended from parts of pixels rather than entire pixels. This is do-able but the result is less pleasing on the eye (edit: because we are not snapping to nice, clean, whole pixel boundaries - which is where changes in color occur).

Vector images draw their pixels using a series of mathematical commands. "Draw from A to B then to C and back to A" makes a triangle. If the ratio of distances between the drawing points is specified, the relationship between the points remains regardless of the image size. When asked to resize in vector terms we are asking the image to be redrawn on a smaller canvas not squishing a larger image into a smaller space.

[klaxxon]

Thank you EER for this professional explanation.
Basically know what it is about, but now things are much clearer.