Image Interpolation with GD 1.x

marcnyc

Hello, can anybody provide me with a funciton that will do bicubic interpolation, or a different interpolation for that matter, to make a resized image look good? I need it to be compatible with GD 1.x (I think I have 1.6) because my host won't update so I can't use the manual's functions like imagecopyresampled(). A function that will work both in GD 1.x and in GD 2.x would be the best but the priority is that it will work in GD 1. I have checked out rze's function in the manual's users' notes but I can't get it to work so please, if anyone can help. Thanks.

Mordecai

imagecopyresized? It's pretty simple:
Quoth the manual, "int imagecopyresized ( resource dst_im, resource src_im, int dstX, int dstY, int srcX, int srcY, int dstW, int dstH, int srcW, int srcH)"

dst_im is the destination image, src_im is the source image. dstX and dstY are the destination of the upper left of the image. srcX and srcY are the upper left point of the source mask. dstW and dstH are the width and height of the image as they are printed onto dst_im. srcW and srcH are the width and height from the source image.
I.e.:
imagecopyresized($im,$oldim,0,0,0,0,200,200,100,100);
This will copy an image from a 100 by 100 image to a 200 by 200 part of another image.

marcnyc

You have obviously misunderstood (or not read at all) my question. I am inquiring about interpolation of an image. With GD 2.x you can do that with imagecopyresampled(). On GD 1.x you need some math to do what imagecopyresampled() does. Some guy in the manual's user note provided a math solution, that even though was questioned is the only one that I have found and doesn't seem to work at all.
If anybody has any idea about how to interpolate on GD 1.x please let me know.

Weedpacket

Well, this is one of the reasons GD2 is available - to provide interpolated scaling 🙂 (It would certainly be far faster than emulating it in PHP).

There is some commentary and a few bugfixes following rze's original function (both on the imagecopyresized and imagecopyresampled pages); I don't know if any of those address your problem (not knowing what your problem looks like).

Meanwhile; start thinking of looking for another host 🙂 - whose reasons for not upgrading are what, exactly? Oh, yes; it would probably break everyone else's GD_Lib scripts.

marcnyc

Hi Weedpacket, I like your new hat...

I know very well that GD 2.x does it but my host doesn't have it and I am tired of moving around. I run a non-profit website and I don't want to pay $10-15 a month just for GD support when I have a good host that is a lot cheaper. I just finished moving there and believe it ain't a piece of cake to move a big site like mine...

My problem is simply that I want the resized thumbnails I am generating to look better than what they do with imagecopyresize.

I have read some of the follow ups of rze's function but I just can't get them to work... it keeps giving me errors. Where you able to make them work?

The guy obviously never answered my email.

Weedpacket

Just had my first crack at it now...

scott's code on [man]imagecopyresampled[/man] worked for me once I'd uncommented the colour allocation code (since with GDLib1.x, I was not working with truecolour images).

marcnyc

Would you be so kind to post the code you used and most importantly an example of how you used the code with an image and how you called the function (what parameters you passed to the function call)...

A couple of weeks ago I spent 3 hours on this and just couldn't get it to work... Always a page full of errors

Weedpacket

The code I used is the one I mentioned, with the change I mentioned, and with this bit before it:

$res = ImageCreatefromPNG('clipboard01.png');
$rt = imageCreate(100,100);
ImageCopyResampleBicubic($rt, $res, 0,0, 0,0, 300,300, 100,200);
ImagePng($rt);

And this file for clipboard.png

marcnyc

THANKS A LOT Weedpacket, your post really explained many things as of why and how I didn't get it to work for me. With your additional code I understood many things...

Now that I got going on this I must move one complaint, not to you but to the quality of the images... I was hoping that using this function would do what Photoshop does instead even if I work with PNG's it looks the resulting images have a corrupted palette of colors, it looks like if in Photoshop you are resizing a fixzed-palette GIF or converting a JPEG to a palette with not enough colors...

To make you understand I am attaching 4 pictures. They were resized from a hi quality digital camera JPEG picture of 1600x1200 where all the colors where nice. I converted the JPEG in PNG inside photoshop, keeping the same size, and the quality and colors were still great.
I tested both scripts (the one by Scott and the one by RZE) and the imags have the words 'scott' or 'rze' in their name to differentiate (I can see no difference between the results with the two codes).
These are the results (I am not posting the originals because one of them is over 2Mb and the other one 500k):

drum_medium_rze.png

drum_medium_scott.png

drum_small_rze.png

drum_small_scott.png

bass_medium_rze.png

bass_medium_scott.png

bass_small_rze.png

bass_small_scott.png

These are the results with JPEGs (not yet as good as Photoshop but definitely better than PNG):

drum_medium_rze.jpg

drum_small_rze.jpg

I had a little better luck with JPEG's, but the above result with the PNG's is quite depressing. Is this normal???

Anyway I ended up using RZE's code because in the notes I saw that he posted a newer code after Scott's that supposingly has a couple of improvements over Scott's code...