I know that this is a complete noob question, but bear with me... I am learning
If I save a PNG file as interlaced will quality be sacrificed compared to a non interlaced version? I tested and sizes are different for the same pixel depth and same width/height.
What about progressive jpeg versus regular? The sizes are also different...
beto wrote:I know that this is a complete noob question, but bear with me... I am learning
If I save a PNG file as interlaced will quality be sacrificed compared to a non interlaced version? I tested and sizes are different for the same pixel depth and same width/height.
What about progressive jpeg versus regular? The sizes are also different...
PNG is a lossless format even if you use interlaced and different compression value.
JPEG is a lossy format progressive or not.
What I meant is comparing PNG interlaced versus PNG non-interlaced and JPEG progressive versus JPEG non-progressive using the same image source.
From your reply I understand that for PNG I will be able to restore the original image source losslessly no matter if I compressed it with PNG interlaced or PNG non-interlaced. Is this correct? The doubt arised because compressing the same image source with PNG interlaced gave me smaller file sizes than compressing it with PNG non-interlaced for the same compression level...
Regarding JPEG what I wanted to know is if JPEG progressive is "more lossy" than JPEG non-progressive for the same image source.
Anonymous wrote:From your reply I understand that for PNG I will be able to restore the original image source losslessly no matter if I compressed it with PNG interlaced or PNG non-interlaced. Is this correct? The doubt arised because compressing the same image source with PNG interlaced gave me smaller file sizes than compressing it with PNG non-interlaced for the same compression level...
Data can perhaps be compressed more when interlaced, but it's lossy.
Regarding JPEG what I wanted to know is if JPEG progressive is "more lossy" than JPEG non-progressive for the same image source.
No it's the same. Progressive jpeg write original picture + pictures at different resolution.
1) PNGs are always lossLESS, regardless of interlaced or not. In most cases, interlacing will increase the filesize, but in some it may reduce it. Interlacing saves the file in a slightly different fashion than non-interlacing and thus results in a different filesize, but it does not change the fact that PNG is lossless. An interlaced PNG and a non-interlaced PNG created from the same source image will be pixel-perfect identical to each other.
(Note: There are some experimental "lossy" png compressors floating around, but these still save lossless files. The loss in these so-called "lossy" PNGs is done before actually creating the file.)
2) The same is essentially true for progressive/non-progressive JPGs. There is no increased loss regardless whether you save the image as progressive or non-progressive. Again, the difference lies only in how the program layers the data within the image file. This results in a different filesize, but no difference within the visible image. Progressive JPGs differ from interlaced PNGs in that a progressive JPG is usually smaller than a non-progressive one. (Unless you are dealing with a very large image, then the non-progressive will usually be smaller.)
In short, the only difference between interlaced/progressive and non-interlaced/non-progressive images is how they display as they're loading, and a minor difference in filesize. Quality is not affected one way or the other.
