I have 2 alpha channels.
I tried to delete the first one, but the "Delete channel" menu item is grayed out.
How could I delete it so that only the last alpha channel still remains?
Thank you.
The top four channels (R,G,B,Alpha) are the results of the full visible image and cannot be altered directly. You can't delete them but they aren't really duplicates anyway...
Also, the channel that you call "alpha" is just a separate channel, and isn't the alpha channel of the image (as it is it has no influence on the visible image, the Channels list is mostly a place where channels are stored for use in further operations). If you want to alter the opacity of the image, you have to add a a layer mask to a layer.
Related
I have sRGB images with color casts. To remove it manually I usually use Photoshop Level Adjustments. Photoshop also have tools for that: Auto Contrast or even better Auto Tone which also takes shadows, midtones & highlights into account.
If I remove the cast manually I adjust each of the RGB channels individually so that the darkest pixels are set to pure black and the lightest to pure white and then redistribute all other values (spreading the histogram). This is a simple approach but shows good results for my images.
In my node.js app I'm using sharp for image processing which uses libvips as its processing engine. I tried to remove the cast with .normalize() but this command works on all channels together and not individual for each of the RGB channels. So it doesn't work for me.
I also asked this question on the sharp project page. I tested the suggestion from lovell to try it with hist_local but the results are not useable for me.
Now I would like to find out how this could be done using the native libvips. I've played around with nip2 GUI and different commands but could not figure out how it could be achieved:
Histogram > Equalise Histogram > Global => Picture looks over saturated
Image > Levels > Scale to 0 - 255 => Channels ar not all spreading from 0 - 255 (I don't understand exactly what this command does?)
Thanks for every hint!
Addition
Here is a example with pictures from Photoshop to show what I want.
The source image is a picture of a frame from a film negative.
Image before processing
Step1 Invert image
Image after inversion
Step2 using Auto tone in Photoshop (works the same way as my description above about manually remove the color cast)
Image after Auto Tone
This last picture is ok for me.
nip2 has a menu item for this.
Load your image and mark a region on it containing the area you'd like to be neutral. It can be any lightness, it doesn't need to be white.
Use File / Open to get the file dialog and you should see the image loaded in your workspace as a thumbnail.
Doubleclick on the thumbnail to open an image view window.
In the view window, zoom and pan to the right spot. The user guide (press F1) has a section on image navigation.
Hold down CTRL and click and drag down and right to mark a rectangular region.
Back in the main window, click Toolkits / Tasks / Capture / White balance. You should see something like:
You can drag an resize your region to change the neutral point. Use the colour picker to set what white means. You can make other whites with (for example) Colour / New / Colour from CCT and link them together.
Click Colour / New / Colour from CCT to make a colour picker from CCT (correlated colour temperature) -- the temperature in Kelvin of that white.
Set it to something interesting, like 4800 for warm white.
Click on the formula for A5.white to edit it, and enter the cell of your CCT widget (A7 in this case).
Now you can drag the region to adjust the pixels to set the neutral from, and drag the CCT slider to set the temperature.
It can be annoying to find things in the toolkit menu. There's a thing for searching toolkits: in the main window, click View / Toolkit browser. You can enter something like "white" and it'll show related toolkit entries.
Here's another answer, but using pyvips and responding to the previous comments. I didn't want to delete the first answer as it still seemed useful.
This version finds the image histogram, searches for thresholds which will select 0.5% and 99.5% of pixels in each image band, then rescales the image so that those pixel values become 0 and 255.
import sys
import pyvips
# trim off this percentage of pixels from the top and bottom
trim_percent = 0.5
def percent(hist, percentage):
"""From a histogram, find the threshold above which lie
#percentage of pixels."""
# normalised cumulative histogram
norm = hist.hist_cum().hist_norm()
# column and row profile over percentage
c, r = (norm > norm.width * percentage / 100).profile()
return r.avg()
image = pyvips.Image.new_from_file(sys.argv[1])
# photographic negative
image = image.invert()
# find image histogram, split to set of separate bands
bands = image.hist_find().bandsplit()
# for each band, the low and high thresholds
low = [percent(band, trim_percent) for band in bands]
high = [percent(band, 100 - trim_percent) for band in bands]
# rescale image
scale = [255.0 / (h - l) for h, l in zip(high, low)]
image = (image - low) * scale
image.write_to_file(sys.argv[2])
It seems to give roughly similar results to the PS button. If I run:
$ ./autolevel.py ~/pics/before.jpg x.jpg
I see:
In the meantime I've found the Simplest Color Balance Algorithm which exactly describes the problem with color casts and there you can also find a C source code.
It is exactly the same solution as John describes in his second answer but as a small piece of c-code.
I'm now trying to use it as C/C++ addon with N-API under node.js.
I am working within Google Earth Engine and am trying to create a no-color/completely transparent color (no boarder and no fill). Below is a line of code where the first color should be the transparent "color". Basically I want my min value to not show up in the map at all.
Map.addLayer(image, {min: 0, max: 3, palette: [transparent, '#0571b0', '#FFDF00', '#ca0020']},'image');
I have tried creating a variable to set a color as completely transparent (change the opacity to 0), but the palette command cannot take variables. Only strings. I've also read SVG fill color transparency, but do not understand how to change the opacity of that specific color without creating a variable (which again, palette doesn't allow). Lastly, I tried adding 00 to the end of another color, but that did not work either.
Any suggestions?
Update:
I was never able to find a solution to this and ended up just going with a white back ground. It was purely for a nicer aesthetic look to allow a basemap to be seen. If I ever come across a solution, I'll be sure to post it.
I had the same question. I found the solution in the developer group.
See the answers: https://groups.google.com/g/google-earth-engine-developers/c/WcxtEIzudxw/m/GscOlsQhDgAJ
The Solution:
// create your previous mask
image = image.eq(1)
// mask and set the opacity
image = image.mask(image.mask().where(image.eq(0),0.0))
I have a couple of questions, which get tied back to a simple need - I want to use the quality histogram as a colorbar in my publication. To export it along with labels for publication, I tried just taking a snapshot with the appropriate tool, but if I use alpha/ solid white background the text/ colorbars is not visible. If I use the solid black or meshlab background, the text is white, or can not be used directly in publication.
My questions are as follows:
I know how to change the text color on meshlab window. Is there a similar function to change the text font size on meshlab window?
As a more demanding question, is there a way I can import the quality map file into matlab or some other software, and plot a custom colorbar. I will append my .qmap file here, but it seems that the color field is empty, and I can not reproduce the colors without them.
%%%%%QMAP FILE TO FOLLOW%%%%%
// COLOR BAND FILE STRUCTURE - first row: RED CHANNEL DATA - second row GREEN CHANNEL DATA - third row: BLUE CHANNEL DATA
// CHANNEL DATA STRUCTURE - the channel structure is grouped in many triples. The items of each triple represent respectively: X VALUE, Y_LOWER VALUE, Y_UPPER VALUE of each node-key of the transfer function
0;0.5;0.125;1;0.375;1;0.625;0;0.875;0;1;0;
0;0;0.125;0;0.375;1;0.625;1;0.875;0;1;0;
0;0;0.125;0;0.375;0;0.625;1;0.875;1;1;0.5;
//THE FOLLOWING 4 VALUES REPRESENT EQUALIZER SETTINGS - the first and the third values represent respectively the minimum and the maximum quality values used in histogram, the second one represent the position (in percentage) of the middle quality, and the last one represent the level of brightness as a floating point number (0 copletely dark, 1 original brightness, 2 completely white)
-0.001;0.714286;0.0004;1;
I imagine there is probably going to be an easy solution for this in GIMP, but I for the life of me can't figure it out.
I'm using the color picker tool with the use info window selected to verify pixel values.
Basically, I have some pixels in an image that I need to zero out. By that I mean I want the RGBA values to all be set to 0.
I attempted to:
use the rectangular select tool to select the group of pixels
use bucket fill to set the pixels to black with opacity set to 0.0
Then, to verify it was done correctly, I use the color picker to test the value of the rectangle I just filled.
Unfortunately, it seems to just contain the previous value. What am I missing here?
The "opacity" of the bucket-fill is the opacity of the paint, not the opacity of the resulting pixels. In other words the less opaque it is, the less visible the result. What you want to do is bucket-fill selection with black, then [delete].
Wondering if there is an easy way to remove a rectangular slice across the entire width of an image using Gimp, and have the resulting hole closed up automatically. I hope that makes sense. If I select a slice across an image and do "cut", it leaves a blank "hole" there. I want the new top and bottom of the image to join and fill that hole, reducing the image height by the amount sliced out.
Any easy way to do this?
Here is a method that is quick and often does what you want:
Cut out the middle, leaving a transparent "hole".
Click anywhere to remove the selection (so the hole is not selected).
Click Image > Zealous crop .
This is going to remove the middle part. However, if you also have transparency in other parts of the image (like around the edges) it's going to remove that transparency too.
I believe you're asking to do something like cut out the middle of a page, leaving the header and footer and have the blank space removed with the cut action, effectively joining the header and footer together.
To my knowledge, I don't believe so. Even if you cut, or delete, that space is still part of the image even without content.
But, you would be able to highlight the top or bottom (or left or right) of the remaining space and drag it to align with the other side. It's not ideal for repetitive tasks, but should get you through if you only have to do it a few times.
Install Python and the Python Imaging Library. Back in GIMP, select and cut the full-width areas you don't want to transparent, and export the image to test.png. Then use this Python code (works only if complete lines are transparent; will not work properly if there are 100%-transparent pixels anywhere other than on a full-width row)—
from PIL import Image
i = Image.open("test.png")
b = i.tobytes()
b2 = ''.join(b[n:n+4] for n in xrange(0,len(b),4) if ord(b[n+3]))
newHeight = len(b2)/i.width/4
i2 = Image.frombytes('RGBA',(i.width,newHeight),b2)
i2.save("test.png")
Then re-load test.png and verify that the areas you cut have gone.
In gimp 2.8.1 you can easily create a new image from a selection. So if you select a rectangular than do a copy (Ctrl-C) and a past in a new image
Edit -> Paste as -> new image (or Ctrl-Shift-V).